[PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Ian Ray]

The host controller driver type value used by the MMC core [1] _mostly_
overlaps with the eMMC device I/O driver strength value [2] as shown in
the table below; however, there is _no_ host mapping for eMMC value 4.

  host value/type   | eMMC value | nominal impedance | strength
  ------------------+------------+-------------------+---------
  0 / Type B        | 0          | 50 Ohm            | x1
  1 / Type A        | 1          | 33 Ohm            | x1.5
  2 / Type C        | 2          | 66 Ohm            | x0.75
  3 / Type D        | 3          | 100 Ohm           | x0.5
  (none)            | 4          | 40 Ohm            | x1.2

[1] MMC_SET_DRIVER_TYPE_* in include/linux/mmc/host.h

[2] 'fixed-emmc-driver-type', see JESD84-B51 Table 206 and
    Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml

Since commit 5a52c5701a67 ("mmc: core: Fix host controller programming
for fixed driver type"), the selected eMMC driver strength is passed
directly to mmc_set_driver_type().  For a fixed eMMC driver type of 4
this reaches sdhci_set_ios(), which only knows types 0..3 and therefore
complains on every ios update:

  mmc2: invalid driver type, default to driver type B

The mmc card itself is still programmed correctly (the HS_TIMING driver
strength field is set from card->drive_strength independently), so this
is a spurious, repeated warning for a valid, documented configuration.

Change to only program the host when the eMMC driver type value maps to
a valid host driver type.

Tested on i.MX8MP (usdhc3, eMMC in HS400) with
`fixed-emmc-driver-type = <4>`: the warning is no longer logged and the
HS_TIMING register contains 0x43 as expected.

Fixes: 5a52c5701a67 ("mmc: core: Fix host controller programming for fixed driver type")
Cc: stable@vger.kernel.org
Signed-off-by: Ian Ray <ian.ray@gehealthcare.com>
---
 drivers/mmc/core/mmc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 05444ecf3909..ff5d4b805998 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1371,9 +1371,11 @@ static void mmc_select_driver_type(struct mmc_card *card)
 
 	card->drive_strength = drive_strength;
 
-	if (fixed_drv_type >= 0 && drive_strength)
-		mmc_set_driver_type(card->host, drive_strength);
-	else if (drv_type)
+	if (fixed_drv_type >= 0 && drive_strength) {
+		/* eMMC driver types >= 4 have no host controller equivalent. */
+		if (drive_strength <= MMC_SET_DRIVER_TYPE_D)
+			mmc_set_driver_type(card->host, drive_strength);
+	} else if (drv_type)
 		mmc_set_driver_type(card->host, drv_type);
 }
 
-- 
2.49.0

Re: [PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Ulf Hansson]

+ Adrian

On Sat, Sep 26, 2026 at 2:29 PM Ian Ray <ian.ray@gehealthcare.com> wrote:
>
> The host controller driver type value used by the MMC core [1] _mostly_
> overlaps with the eMMC device I/O driver strength value [2] as shown in
> the table below; however, there is _no_ host mapping for eMMC value 4.

I think the mapping exists only because that is what the SD spec
provided when this was introduced.

We can certainly add something that corresponds to value 4 from the
eMMC spec as well, to make this complete.

>
>   host value/type   | eMMC value | nominal impedance | strength
>   ------------------+------------+-------------------+---------
>   0 / Type B        | 0          | 50 Ohm            | x1
>   1 / Type A        | 1          | 33 Ohm            | x1.5
>   2 / Type C        | 2          | 66 Ohm            | x0.75
>   3 / Type D        | 3          | 100 Ohm           | x0.5
>   (none)            | 4          | 40 Ohm            | x1.2
>
> [1] MMC_SET_DRIVER_TYPE_* in include/linux/mmc/host.h
>
> [2] 'fixed-emmc-driver-type', see JESD84-B51 Table 206 and
>
>
> Since commit 5a52c5701a67 ("mmc: core: Fix host controller programming
> for fixed driver type"), the selected eMMC driver strength is passed
> directly to mmc_set_driver_type().  For a fixed eMMC driver type of 4
> this reaches sdhci_set_ios(), which only knows types 0..3 and therefore
> complains on every ios update:
>
>   mmc2: invalid driver type, default to driver type B

Perhaps the print above from sdhci_set_ios() is simply a bit
misleading. For example, it looks like arasan_select_phy_clock()
actually uses the value in ios.drv_type as is.

To me, it looks like the problem is that mmc_select_drive_strength()
doesn't really do its job correctly, as it should help us to figure
out what is supported by the card *and* by the host, so we can request
a proper driver type when calling the ->set_ios() callback.

>
> The mmc card itself is still programmed correctly (the HS_TIMING driver
> strength field is set from card->drive_strength independently), so this
> is a spurious, repeated warning for a valid, documented configuration.
>
> Change to only program the host when the eMMC driver type value maps to
> a valid host driver type.
>
> Tested on i.MX8MP (usdhc3, eMMC in HS400) with
> `fixed-emmc-driver-type = <4>`: the warning is no longer logged and the
> HS_TIMING register contains 0x43 as expected.
>
> Fixes: 5a52c5701a67 ("mmc: core: Fix host controller programming for fixed driver type")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ian Ray <ian.ray@gehealthcare.com>

I have looped in Adrian, to get his opinion on this.

Kind regards
Uffe

> ---
>  drivers/mmc/core/mmc.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 05444ecf3909..ff5d4b805998 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1371,9 +1371,11 @@ static void mmc_select_driver_type(struct mmc_card *card)
>
>         card->drive_strength = drive_strength;
>
> -       if (fixed_drv_type >= 0 && drive_strength)
> -               mmc_set_driver_type(card->host, drive_strength);
> -       else if (drv_type)
> +       if (fixed_drv_type >= 0 && drive_strength) {
> +               /* eMMC driver types >= 4 have no host controller equivalent. */
> +               if (drive_strength <= MMC_SET_DRIVER_TYPE_D)
> +                       mmc_set_driver_type(card->host, drive_strength);
> +       } else if (drv_type)
>                 mmc_set_driver_type(card->host, drv_type);
>  }
>
> --
> 2.49.0
>

Re: [PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Adrian Hunter]

On 29/09/2026 16:06, Ulf Hansson wrote:
> + Adrian
> 
> On Sat, Sep 26, 2026 at 2:29 PM Ian Ray <ian.ray@gehealthcare.com> wrote:
>>
>> The host controller driver type value used by the MMC core [1] _mostly_
>> overlaps with the eMMC device I/O driver strength value [2] as shown in
>> the table below; however, there is _no_ host mapping for eMMC value 4.
> 
> I think the mapping exists only because that is what the SD spec
> provided when this was introduced.
> 
> We can certainly add something that corresponds to value 4 from the
> eMMC spec as well, to make this complete.
> 
>>
>>   host value/type   | eMMC value | nominal impedance | strength
>>   ------------------+------------+-------------------+---------
>>   0 / Type B        | 0          | 50 Ohm            | x1
>>   1 / Type A        | 1          | 33 Ohm            | x1.5
>>   2 / Type C        | 2          | 66 Ohm            | x0.75
>>   3 / Type D        | 3          | 100 Ohm           | x0.5
>>   (none)            | 4          | 40 Ohm            | x1.2
>>
>> [1] MMC_SET_DRIVER_TYPE_* in include/linux/mmc/host.h
>>
>> [2] 'fixed-emmc-driver-type', see JESD84-B51 Table 206 and
>>
>>
>> Since commit 5a52c5701a67 ("mmc: core: Fix host controller programming
>> for fixed driver type"), the selected eMMC driver strength is passed
>> directly to mmc_set_driver_type().  For a fixed eMMC driver type of 4
>> this reaches sdhci_set_ios(), which only knows types 0..3 and therefore
>> complains on every ios update:
>>
>>   mmc2: invalid driver type, default to driver type B
> 
> Perhaps the print above from sdhci_set_ios() is simply a bit
> misleading. For example, it looks like arasan_select_phy_clock()
> actually uses the value in ios.drv_type as is.
> 
> To me, it looks like the problem is that mmc_select_drive_strength()
> doesn't really do its job correctly, as it should help us to figure
> out what is supported by the card *and* by the host, so we can request
> a proper driver type when calling the ->set_ios() callback.

mmc_select_drive_strength() returns the card value directly and
the host value in *drv_type.

fixed-emmc-driver-type as described by
Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
doesn't mention the host controller, and the original commits
6186d06c519e2 "mmc: parse new binding for eMMC fixed driver type"
be17f1ce8572d "mmc: core: properly init drv_type" seemingly
deliberately left it alone.

5a52c5701a67d "mmc: core: Fix host controller programming for
fixed driver type" introduces a new policy: fixed-emmc-driver-type
is a host controller setting also.

If that was done by mmc_select_drive_strength(), it would look
something like below ( note it no longer allows fixed_drv_type to override
->select_drive_strength() , and fixed-emmc-driver-type will then hit
any nonremovable SD or SDIO ):

int mmc_select_drive_strength(struct mmc_card *card, unsigned int max_dtr,
			      int card_drv_type, int *drv_type)
{
	struct mmc_host *host = card->host;
	int fixed_drv_type = host->fixed_drv_type;
	int host_drv_type = SD_DRIVER_TYPE_B;

	*drv_type = 0;

	if (!host->ops->select_drive_strength) {
		if (fixed_drv_type >= 0 &&
		    (card_drv_type & mmc_driver_type_mask(fixed_drv_type))) {
			*drv_type = fixed_drv_type;
			return fixed_drv_type;
		}
		return 0;
	}

	/* Use SD definition of driver strength for hosts */
	if (host->caps & MMC_CAP_DRIVER_TYPE_A)
		host_drv_type |= SD_DRIVER_TYPE_A;

	if (host->caps & MMC_CAP_DRIVER_TYPE_C)
		host_drv_type |= SD_DRIVER_TYPE_C;

	if (host->caps & MMC_CAP_DRIVER_TYPE_D)
		host_drv_type |= SD_DRIVER_TYPE_D;

	/*
	 * The drive strength that the hardware can support
	 * depends on the board design.  Pass the appropriate
	 * information and let the hardware specific code
	 * return what is possible given the options
	 */
	return host->ops->select_drive_strength(card, max_dtr,
						host_drv_type,
						card_drv_type,
						drv_type);
}

and:

static void mmc_select_driver_type(struct mmc_card *card)
{
	int card_drv_type, drive_strength, drv_type = 0;

	card_drv_type = card->ext_csd.raw_driver_strength |
			mmc_driver_type_mask(0);

	drive_strength = mmc_select_drive_strength(card,
						   card->ext_csd.hs200_max_dtr,
						   card_drv_type, &drv_type);

	card->drive_strength = drive_strength;

	if (drv_type)
		mmc_set_driver_type(card->host, drv_type);
}

But that doesn't help with drivers where the controller does
do not support the value passed by fixed-emmc-driver-type even
though the card does.  mmc_select_drive_strength() has no way
of knowing that.  The ->select_drive_strength() callback
allows selecting different values. fixed-emmc-driver-type is
one value.

The warning in sdhci.c seems correct.  SDHCI is an SD standard,
so doesn't define value 4 (and only has 2 bits for the field).
The selected driver strength is not being programmed - deserves
a warning.

Perhaps if the affected driver implements
->select_drive_strength():

static int ???_select_drive_strength(struct mmc_card *card,
				     unsigned int max_dtr, int host_drv,
				     int card_drv, int *host_driver_strength)
{
	struct mmc_host *host = card->host;
	int fixed_drv_type = host->fixed_drv_type;

	if (fixed_drv_type >= 0 &&
	    (card_drv & mmc_driver_type_mask(fixed_drv_type))) {
		if (fixed_drv_type == 4)
			*drv_type = MMC_SET_DRIVER_TYPE_B;
		else
			*drv_type = fixed_drv_type;
		return fixed_drv_type;
	}
	return 0;
}

But that requires the changes to
mmc_select_drive_strength() and mmc_select_driver_type()
above (with its caveats), so that ->select_drive_strength()
overrides fixed-emmc-driver-type.  That would be fine for
drivers/mmc/host/sdhci-pci-core.c, and probably
amd_select_drive_strength(), but it is starting to get
complicated.

A simpler alternative is for the affected driver to hook
->set_ios() and fix up the value.

void ???_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
{
	if (ios->drv_type == 4)
		ios->drv_type = MMC_SET_DRIVER_TYPE_B;

	return sdhci_set_ios(mmc, ios);
}

And in probe (assuming struct sdhci_host *host):

	host->mmc_host_ops.set_ios = ???_set_ios;


> 
>>
>> The mmc card itself is still programmed correctly (the HS_TIMING driver
>> strength field is set from card->drive_strength independently), so this
>> is a spurious, repeated warning for a valid, documented configuration.
>>
>> Change to only program the host when the eMMC driver type value maps to
>> a valid host driver type.
>>
>> Tested on i.MX8MP (usdhc3, eMMC in HS400) with
>> `fixed-emmc-driver-type = <4>`: the warning is no longer logged and the
>> HS_TIMING register contains 0x43 as expected.
>>
>> Fixes: 5a52c5701a67 ("mmc: core: Fix host controller programming for fixed driver type")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Ian Ray <ian.ray@gehealthcare.com>
> 
> I have looped in Adrian, to get his opinion on this.
> 
> Kind regards
> Uffe
> 
>> ---
>>  drivers/mmc/core/mmc.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index 05444ecf3909..ff5d4b805998 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -1371,9 +1371,11 @@ static void mmc_select_driver_type(struct mmc_card *card)
>>
>>         card->drive_strength = drive_strength;
>>
>> -       if (fixed_drv_type >= 0 && drive_strength)
>> -               mmc_set_driver_type(card->host, drive_strength);
>> -       else if (drv_type)
>> +       if (fixed_drv_type >= 0 && drive_strength) {
>> +               /* eMMC driver types >= 4 have no host controller equivalent. */
>> +               if (drive_strength <= MMC_SET_DRIVER_TYPE_D)
>> +                       mmc_set_driver_type(card->host, drive_strength);
>> +       } else if (drv_type)
>>                 mmc_set_driver_type(card->host, drv_type);
>>  }
>>
>> --
>> 2.49.0
>>

Re: [PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Ian Ray]

On Wed, Sep 30, 2026 at 10:00:47PM +0300, Adrian Hunter wrote:
> On 29/09/2026 16:06, Ulf Hansson wrote:
> > + Adrian
> >
> > On Sat, Sep 26, 2026 at 2:29 PM Ian Ray <ian.ray@gehealthcare.com> wrote:
> >>
> >> The host controller driver type value used by the MMC core [1] _mostly_
> >> overlaps with the eMMC device I/O driver strength value [2] as shown in
> >> the table below; however, there is _no_ host mapping for eMMC value 4.
> >
> > I think the mapping exists only because that is what the SD spec
> > provided when this was introduced.
> >
> > We can certainly add something that corresponds to value 4 from the
> > eMMC spec as well, to make this complete.
> >
> >>
> >>   host value/type   | eMMC value | nominal impedance | strength
> >>   ------------------+------------+-------------------+---------
> >>   0 / Type B        | 0          | 50 Ohm            | x1
> >>   1 / Type A        | 1          | 33 Ohm            | x1.5
> >>   2 / Type C        | 2          | 66 Ohm            | x0.75
> >>   3 / Type D        | 3          | 100 Ohm           | x0.5
> >>   (none)            | 4          | 40 Ohm            | x1.2
> >>
> >> [1] MMC_SET_DRIVER_TYPE_* in include/linux/mmc/host.h
> >>
> >> [2] 'fixed-emmc-driver-type', see JESD84-B51 Table 206 and
> >>
> >>
> >> Since commit 5a52c5701a67 ("mmc: core: Fix host controller programming
> >> for fixed driver type"), the selected eMMC driver strength is passed
> >> directly to mmc_set_driver_type().  For a fixed eMMC driver type of 4
> >> this reaches sdhci_set_ios(), which only knows types 0..3 and therefore
> >> complains on every ios update:
> >>
> >>   mmc2: invalid driver type, default to driver type B
> >
> > Perhaps the print above from sdhci_set_ios() is simply a bit
> > misleading. For example, it looks like arasan_select_phy_clock()
> > actually uses the value in ios.drv_type as is.
> >
> > To me, it looks like the problem is that mmc_select_drive_strength()
> > doesn't really do its job correctly, as it should help us to figure
> > out what is supported by the card *and* by the host, so we can request
> > a proper driver type when calling the ->set_ios() callback.
> 
> mmc_select_drive_strength() returns the card value directly and
> the host value in *drv_type.
> 
> fixed-emmc-driver-type as described by
> Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
> doesn't mention the host controller, and the original commits
> 6186d06c519e2 "mmc: parse new binding for eMMC fixed driver type"
> be17f1ce8572d "mmc: core: properly init drv_type" seemingly
> deliberately left it alone.
> 
> 5a52c5701a67d "mmc: core: Fix host controller programming for
> fixed driver type" introduces a new policy: fixed-emmc-driver-type
> is a host controller setting also.
> 
> If that was done by mmc_select_drive_strength(), it would look
> something like below ( note it no longer allows fixed_drv_type to override
> ->select_drive_strength() , and fixed-emmc-driver-type will then hit
> any nonremovable SD or SDIO ):
> 
> int mmc_select_drive_strength(struct mmc_card *card, unsigned int max_dtr,
>                               int card_drv_type, int *drv_type)
> {
>         struct mmc_host *host = card->host;
>         int fixed_drv_type = host->fixed_drv_type;
>         int host_drv_type = SD_DRIVER_TYPE_B;
> 
>         *drv_type = 0;
> 
>         if (!host->ops->select_drive_strength) {
>                 if (fixed_drv_type >= 0 &&
>                     (card_drv_type & mmc_driver_type_mask(fixed_drv_type))) {
>                         *drv_type = fixed_drv_type;
>                         return fixed_drv_type;
>                 }
>                 return 0;
>         }
> 
>         /* Use SD definition of driver strength for hosts */
>         if (host->caps & MMC_CAP_DRIVER_TYPE_A)
>                 host_drv_type |= SD_DRIVER_TYPE_A;
> 
>         if (host->caps & MMC_CAP_DRIVER_TYPE_C)
>                 host_drv_type |= SD_DRIVER_TYPE_C;
> 
>         if (host->caps & MMC_CAP_DRIVER_TYPE_D)
>                 host_drv_type |= SD_DRIVER_TYPE_D;
> 
>         /*
>          * The drive strength that the hardware can support
>          * depends on the board design.  Pass the appropriate
>          * information and let the hardware specific code
>          * return what is possible given the options
>          */
>         return host->ops->select_drive_strength(card, max_dtr,
>                                                 host_drv_type,
>                                                 card_drv_type,
>                                                 drv_type);
> }
> 
> and:
> 
> static void mmc_select_driver_type(struct mmc_card *card)
> {
>         int card_drv_type, drive_strength, drv_type = 0;
> 
>         card_drv_type = card->ext_csd.raw_driver_strength |
>                         mmc_driver_type_mask(0);
> 
>         drive_strength = mmc_select_drive_strength(card,
>                                                    card->ext_csd.hs200_max_dtr,
>                                                    card_drv_type, &drv_type);
> 
>         card->drive_strength = drive_strength;
> 
>         if (drv_type)
>                 mmc_set_driver_type(card->host, drv_type);
> }
> 
> But that doesn't help with drivers where the controller does
> do not support the value passed by fixed-emmc-driver-type even
> though the card does.  mmc_select_drive_strength() has no way
> of knowing that.  The ->select_drive_strength() callback
> allows selecting different values. fixed-emmc-driver-type is
> one value.
> 
> The warning in sdhci.c seems correct.  SDHCI is an SD standard,
> so doesn't define value 4 (and only has 2 bits for the field).
> The selected driver strength is not being programmed - deserves
> a warning.
> 
> Perhaps if the affected driver implements
> ->select_drive_strength():
> 
> static int ???_select_drive_strength(struct mmc_card *card,
>                                      unsigned int max_dtr, int host_drv,
>                                      int card_drv, int *host_driver_strength)
> {
>         struct mmc_host *host = card->host;
>         int fixed_drv_type = host->fixed_drv_type;
> 
>         if (fixed_drv_type >= 0 &&
>             (card_drv & mmc_driver_type_mask(fixed_drv_type))) {
>                 if (fixed_drv_type == 4)
>                         *drv_type = MMC_SET_DRIVER_TYPE_B;
>                 else
>                         *drv_type = fixed_drv_type;
>                 return fixed_drv_type;
>         }
>         return 0;
> }
> 
> But that requires the changes to
> mmc_select_drive_strength() and mmc_select_driver_type()
> above (with its caveats), so that ->select_drive_strength()
> overrides fixed-emmc-driver-type.  That would be fine for
> drivers/mmc/host/sdhci-pci-core.c, and probably
> amd_select_drive_strength(), but it is starting to get
> complicated.
> 
> A simpler alternative is for the affected driver to hook
> ->set_ios() and fix up the value.
> 
> void ???_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> {
>         if (ios->drv_type == 4)
>                 ios->drv_type = MMC_SET_DRIVER_TYPE_B;
> 
>         return sdhci_set_ios(mmc, ios);
> }
> 
> And in probe (assuming struct sdhci_host *host):
> 
>         host->mmc_host_ops.set_ios = ???_set_ios;
> 

Thank you for the feedback.

The "invalid driver type" warning that I originally observed originates
in sdhci_set_ios_common() which is shared by all SDHCI hosts (IIUC).

Thus any SDHCI host configured with `fixed-emmc-driver-type = <4>` would
log that warning.

The affected driver for my scenario is sdhci-esdhc-imx.c, and the
proposed change (below) suppresses the warning.

But I am hesitant to open-code the same fixup in every SDHCI driver.
And I am unsure whether this belongs per-driver, or whether the right
fix is in the core / or to the warning itself.

Comments welcome!

drivers/mmc/host/sdhci-esdhc-imx.c

```
static void sdhci_esdhc_imx_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
{
       /*
        * A drv_type of 4 reaches this callback only via the eMMC
        * 'fixed-emmc-driver-type' path: it is the eMMC I/O driver strength
        * value 4 (40 Ohm, see JESD84-B51 Table 206), which has no equivalent
        * host driver type in the SD standard that SDHCI implements (only
        * types B/A/C/D are defined).  Map it to the default Type B here to
        * avoid an "invalid driver type" warning from sdhci_set_ios().  The
        * card's HS_TIMING field is programmed separately from
        * card->drive_strength and is unaffected.
        */
       if (ios->drv_type == 4)
               ios->drv_type = MMC_SET_DRIVER_TYPE_B;

       sdhci_set_ios(mmc, ios);
}

static int sdhci_esdhc_imx_probe(struct platform_device *pdev)
{
...
               /*
                * Support fix up of eMMC driver types which have no SDHCI
                * host driver type equivalent.
                */
               host->mmc_host_ops.set_ios = sdhci_esdhc_imx_set_ios;

```

> 
> >
> >>
> >> The mmc card itself is still programmed correctly (the HS_TIMING driver
> >> strength field is set from card->drive_strength independently), so this
> >> is a spurious, repeated warning for a valid, documented configuration.
> >>
> >> Change to only program the host when the eMMC driver type value maps to
> >> a valid host driver type.
> >>
> >> Tested on i.MX8MP (usdhc3, eMMC in HS400) with
> >> `fixed-emmc-driver-type = <4>`: the warning is no longer logged and the
> >> HS_TIMING register contains 0x43 as expected.
> >>
> >> Fixes: 5a52c5701a67 ("mmc: core: Fix host controller programming for fixed driver type")
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Ian Ray <ian.ray@gehealthcare.com>
> >
> > I have looped in Adrian, to get his opinion on this.
> >
> > Kind regards
> > Uffe
> >
> >> ---
> >>  drivers/mmc/core/mmc.c | 8 +++++---
> >>  1 file changed, 5 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> >> index 05444ecf3909..ff5d4b805998 100644
> >> --- a/drivers/mmc/core/mmc.c
> >> +++ b/drivers/mmc/core/mmc.c
> >> @@ -1371,9 +1371,11 @@ static void mmc_select_driver_type(struct mmc_card *card)
> >>
> >>         card->drive_strength = drive_strength;
> >>
> >> -       if (fixed_drv_type >= 0 && drive_strength)
> >> -               mmc_set_driver_type(card->host, drive_strength);
> >> -       else if (drv_type)
> >> +       if (fixed_drv_type >= 0 && drive_strength) {
> >> +               /* eMMC driver types >= 4 have no host controller equivalent. */
> >> +               if (drive_strength <= MMC_SET_DRIVER_TYPE_D)
> >> +                       mmc_set_driver_type(card->host, drive_strength);
> >> +       } else if (drv_type)
> >>                 mmc_set_driver_type(card->host, drv_type);
> >>  }
> >>
> >> --
> >> 2.49.0
> >>
> 

Re: [PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Adrian Hunter]

On 01/10/2026 18:39, Ian Ray wrote:
> On Wed, Sep 30, 2026 at 10:00:47PM +0300, Adrian Hunter wrote:
>> On 29/09/2026 16:06, Ulf Hansson wrote:
>>> + Adrian
>>>
>>> On Sat, Sep 26, 2026 at 2:29 PM Ian Ray <ian.ray@gehealthcare.com> wrote:
>>>>
>>>> The host controller driver type value used by the MMC core [1] _mostly_
>>>> overlaps with the eMMC device I/O driver strength value [2] as shown in
>>>> the table below; however, there is _no_ host mapping for eMMC value 4.
>>>
>>> I think the mapping exists only because that is what the SD spec
>>> provided when this was introduced.
>>>
>>> We can certainly add something that corresponds to value 4 from the
>>> eMMC spec as well, to make this complete.
>>>
>>>>
>>>>   host value/type   | eMMC value | nominal impedance | strength
>>>>   ------------------+------------+-------------------+---------
>>>>   0 / Type B        | 0          | 50 Ohm            | x1
>>>>   1 / Type A        | 1          | 33 Ohm            | x1.5
>>>>   2 / Type C        | 2          | 66 Ohm            | x0.75
>>>>   3 / Type D        | 3          | 100 Ohm           | x0.5
>>>>   (none)            | 4          | 40 Ohm            | x1.2
>>>>
>>>> [1] MMC_SET_DRIVER_TYPE_* in include/linux/mmc/host.h
>>>>
>>>> [2] 'fixed-emmc-driver-type', see JESD84-B51 Table 206 and
>>>>
>>>>
>>>> Since commit 5a52c5701a67 ("mmc: core: Fix host controller programming
>>>> for fixed driver type"), the selected eMMC driver strength is passed
>>>> directly to mmc_set_driver_type().  For a fixed eMMC driver type of 4
>>>> this reaches sdhci_set_ios(), which only knows types 0..3 and therefore
>>>> complains on every ios update:
>>>>
>>>>   mmc2: invalid driver type, default to driver type B
>>>
>>> Perhaps the print above from sdhci_set_ios() is simply a bit
>>> misleading. For example, it looks like arasan_select_phy_clock()
>>> actually uses the value in ios.drv_type as is.
>>>
>>> To me, it looks like the problem is that mmc_select_drive_strength()
>>> doesn't really do its job correctly, as it should help us to figure
>>> out what is supported by the card *and* by the host, so we can request
>>> a proper driver type when calling the ->set_ios() callback.
>>
>> mmc_select_drive_strength() returns the card value directly and
>> the host value in *drv_type.
>>
>> fixed-emmc-driver-type as described by
>> Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> doesn't mention the host controller, and the original commits
>> 6186d06c519e2 "mmc: parse new binding for eMMC fixed driver type"
>> be17f1ce8572d "mmc: core: properly init drv_type" seemingly
>> deliberately left it alone.
>>
>> 5a52c5701a67d "mmc: core: Fix host controller programming for
>> fixed driver type" introduces a new policy: fixed-emmc-driver-type
>> is a host controller setting also.
>>
>> If that was done by mmc_select_drive_strength(), it would look
>> something like below ( note it no longer allows fixed_drv_type to override
>> ->select_drive_strength() , and fixed-emmc-driver-type will then hit
>> any nonremovable SD or SDIO ):
>>
>> int mmc_select_drive_strength(struct mmc_card *card, unsigned int max_dtr,
>>                               int card_drv_type, int *drv_type)
>> {
>>         struct mmc_host *host = card->host;
>>         int fixed_drv_type = host->fixed_drv_type;
>>         int host_drv_type = SD_DRIVER_TYPE_B;
>>
>>         *drv_type = 0;
>>
>>         if (!host->ops->select_drive_strength) {
>>                 if (fixed_drv_type >= 0 &&
>>                     (card_drv_type & mmc_driver_type_mask(fixed_drv_type))) {
>>                         *drv_type = fixed_drv_type;
>>                         return fixed_drv_type;
>>                 }
>>                 return 0;
>>         }
>>
>>         /* Use SD definition of driver strength for hosts */
>>         if (host->caps & MMC_CAP_DRIVER_TYPE_A)
>>                 host_drv_type |= SD_DRIVER_TYPE_A;
>>
>>         if (host->caps & MMC_CAP_DRIVER_TYPE_C)
>>                 host_drv_type |= SD_DRIVER_TYPE_C;
>>
>>         if (host->caps & MMC_CAP_DRIVER_TYPE_D)
>>                 host_drv_type |= SD_DRIVER_TYPE_D;
>>
>>         /*
>>          * The drive strength that the hardware can support
>>          * depends on the board design.  Pass the appropriate
>>          * information and let the hardware specific code
>>          * return what is possible given the options
>>          */
>>         return host->ops->select_drive_strength(card, max_dtr,
>>                                                 host_drv_type,
>>                                                 card_drv_type,
>>                                                 drv_type);
>> }
>>
>> and:
>>
>> static void mmc_select_driver_type(struct mmc_card *card)
>> {
>>         int card_drv_type, drive_strength, drv_type = 0;
>>
>>         card_drv_type = card->ext_csd.raw_driver_strength |
>>                         mmc_driver_type_mask(0);
>>
>>         drive_strength = mmc_select_drive_strength(card,
>>                                                    card->ext_csd.hs200_max_dtr,
>>                                                    card_drv_type, &drv_type);
>>
>>         card->drive_strength = drive_strength;
>>
>>         if (drv_type)
>>                 mmc_set_driver_type(card->host, drv_type);
>> }
>>
>> But that doesn't help with drivers where the controller does
>> do not support the value passed by fixed-emmc-driver-type even
>> though the card does.  mmc_select_drive_strength() has no way
>> of knowing that.  The ->select_drive_strength() callback
>> allows selecting different values. fixed-emmc-driver-type is
>> one value.
>>
>> The warning in sdhci.c seems correct.  SDHCI is an SD standard,
>> so doesn't define value 4 (and only has 2 bits for the field).
>> The selected driver strength is not being programmed - deserves
>> a warning.
>>
>> Perhaps if the affected driver implements
>> ->select_drive_strength():
>>
>> static int ???_select_drive_strength(struct mmc_card *card,
>>                                      unsigned int max_dtr, int host_drv,
>>                                      int card_drv, int *host_driver_strength)
>> {
>>         struct mmc_host *host = card->host;
>>         int fixed_drv_type = host->fixed_drv_type;
>>
>>         if (fixed_drv_type >= 0 &&
>>             (card_drv & mmc_driver_type_mask(fixed_drv_type))) {
>>                 if (fixed_drv_type == 4)
>>                         *drv_type = MMC_SET_DRIVER_TYPE_B;
>>                 else
>>                         *drv_type = fixed_drv_type;
>>                 return fixed_drv_type;
>>         }
>>         return 0;
>> }
>>
>> But that requires the changes to
>> mmc_select_drive_strength() and mmc_select_driver_type()
>> above (with its caveats), so that ->select_drive_strength()
>> overrides fixed-emmc-driver-type.  That would be fine for
>> drivers/mmc/host/sdhci-pci-core.c, and probably
>> amd_select_drive_strength(), but it is starting to get
>> complicated.
>>
>> A simpler alternative is for the affected driver to hook
>> ->set_ios() and fix up the value.
>>
>> void ???_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>> {
>>         if (ios->drv_type == 4)
>>                 ios->drv_type = MMC_SET_DRIVER_TYPE_B;
>>
>>         return sdhci_set_ios(mmc, ios);
>> }
>>
>> And in probe (assuming struct sdhci_host *host):
>>
>>         host->mmc_host_ops.set_ios = ???_set_ios;
>>
> 
> Thank you for the feedback.
> 
> The "invalid driver type" warning that I originally observed originates
> in sdhci_set_ios_common() which is shared by all SDHCI hosts (IIUC).
> 
> Thus any SDHCI host configured with `fixed-emmc-driver-type = <4>` would
> log that warning.

The warning is valid.  SDHCI does not support value 4 and doesn't know
what is a valid alternative or even if there is one.  That is up to the
driver to sort out.  If other drivers do it the same way, then a
helper or something could be added.

> 
> The affected driver for my scenario is sdhci-esdhc-imx.c, and the
> proposed change (below) suppresses the warning.
> 
> But I am hesitant to open-code the same fixup in every SDHCI driver.
> And I am unsure whether this belongs per-driver, or whether the right
> fix is in the core / or to the warning itself.
> 
> Comments welcome!
> 
> drivers/mmc/host/sdhci-esdhc-imx.c
> 
> ```
> static void sdhci_esdhc_imx_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> {
>        /*
>         * A drv_type of 4 reaches this callback only via the eMMC
>         * 'fixed-emmc-driver-type' path: it is the eMMC I/O driver strength
>         * value 4 (40 Ohm, see JESD84-B51 Table 206), which has no equivalent
>         * host driver type in the SD standard that SDHCI implements (only
>         * types B/A/C/D are defined).  Map it to the default Type B here to
>         * avoid an "invalid driver type" warning from sdhci_set_ios().  The

The objective is not to avoid the warning.  The warning is valid.  The
objective is to provide a valid value.  4 is not.

If the actual value doesn't matter here at all, then say so and set
it to MMC_SET_DRIVER_TYPE_B always.

>         * card's HS_TIMING field is programmed separately from
>         * card->drive_strength and is unaffected.
>         */
>        if (ios->drv_type == 4)
>                ios->drv_type = MMC_SET_DRIVER_TYPE_B;
> 
>        sdhci_set_ios(mmc, ios);
> }
> 
> static int sdhci_esdhc_imx_probe(struct platform_device *pdev)
> {
> ...
>                /*
>                 * Support fix up of eMMC driver types which have no SDHCI
>                 * host driver type equivalent.
>                 */
>                host->mmc_host_ops.set_ios = sdhci_esdhc_imx_set_ios;
> 
> ```
> 
>>
>>>
>>>>
>>>> The mmc card itself is still programmed correctly (the HS_TIMING driver
>>>> strength field is set from card->drive_strength independently), so this
>>>> is a spurious, repeated warning for a valid, documented configuration.
>>>>
>>>> Change to only program the host when the eMMC driver type value maps to
>>>> a valid host driver type.
>>>>
>>>> Tested on i.MX8MP (usdhc3, eMMC in HS400) with
>>>> `fixed-emmc-driver-type = <4>`: the warning is no longer logged and the
>>>> HS_TIMING register contains 0x43 as expected.
>>>>
>>>> Fixes: 5a52c5701a67 ("mmc: core: Fix host controller programming for fixed driver type")
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Ian Ray <ian.ray@gehealthcare.com>
>>>
>>> I have looped in Adrian, to get his opinion on this.
>>>
>>> Kind regards
>>> Uffe
>>>
>>>> ---
>>>>  drivers/mmc/core/mmc.c | 8 +++++---
>>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>>> index 05444ecf3909..ff5d4b805998 100644
>>>> --- a/drivers/mmc/core/mmc.c
>>>> +++ b/drivers/mmc/core/mmc.c
>>>> @@ -1371,9 +1371,11 @@ static void mmc_select_driver_type(struct mmc_card *card)
>>>>
>>>>         card->drive_strength = drive_strength;
>>>>
>>>> -       if (fixed_drv_type >= 0 && drive_strength)
>>>> -               mmc_set_driver_type(card->host, drive_strength);
>>>> -       else if (drv_type)
>>>> +       if (fixed_drv_type >= 0 && drive_strength) {
>>>> +               /* eMMC driver types >= 4 have no host controller equivalent. */
>>>> +               if (drive_strength <= MMC_SET_DRIVER_TYPE_D)
>>>> +                       mmc_set_driver_type(card->host, drive_strength);
>>>> +       } else if (drv_type)
>>>>                 mmc_set_driver_type(card->host, drv_type);
>>>>  }
>>>>
>>>> --
>>>> 2.49.0
>>>>
>>

Re: [PATCH] mmc: core: Don't program invalid host driver type for fixed eMMC type

[Ian Ray]

On Tue, Oct 06, 2026 at 10:28:23AM +0300, Adrian Hunter wrote:
> On 01/10/2026 18:39, Ian Ray wrote:
> > On Wed, Sep 30, 2026 at 10:00:47PM +0300, Adrian Hunter wrote:
> >> On 29/09/2026 16:06, Ulf Hansson wrote:
> >>> + Adrian
> >>>
> >>> On Sat, Sep 26, 2026 at 2:29 PM Ian Ray <ian.ray@gehealthcare.com> wrote:
> >>>>
> >>>> The host controller driver type value used by the MMC core [1] _mostly_
> >>>> overlaps with the eMMC device I/O driver strength value [2] as shown in
> >>>> the table below; however, there is _no_ host mapping for eMMC value 4.
[...]
> >
> > The "invalid driver type" warning that I originally observed originates
> > in sdhci_set_ios_common() which is shared by all SDHCI hosts (IIUC).
> >
> > Thus any SDHCI host configured with `fixed-emmc-driver-type = <4>` would
> > log that warning.
> 
> The warning is valid.  SDHCI does not support value 4 and doesn't know
> what is a valid alternative or even if there is one.  That is up to the
> driver to sort out.  If other drivers do it the same way, then a
> helper or something could be added.
[...]
> The objective is not to avoid the warning.  The warning is valid.  The
> objective is to provide a valid value.  4 is not.
 
Thank you, I will send a v2 in which sdhci_esdhc_imx_set_ios implements
a bounds check against MMC_SET_DRIVER_TYPE_D.