[PATCH] mmc: core: Add a capability for disabling mmc cards

[PATCH] mmc: core: Add a capability for disabling mmc cards

[Adam Lee]

On some systems we need a way to disable MMC card support in a MMC/SD
card slot due to the legal concern.

Add support in the core SD/MMC code to support this.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Adam Lee <adam.lee@canonical.com>
---
 drivers/mmc/core/core.c  |    2 +-
 include/linux/mmc/host.h |    1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index c40396f..4788b88 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2271,7 +2271,7 @@ static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
 		return 0;
 	if (!mmc_attach_sd(host))
 		return 0;
-	if (!mmc_attach_mmc(host))
+	if (!(host->caps2 & MMC_CAP2_NO_MMC) && !mmc_attach_mmc(host))
 		return 0;
 
 	mmc_power_off(host);
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index e326ae2..ffe5c3d 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -281,6 +281,7 @@ struct mmc_host {
 #define MMC_CAP2_PACKED_CMD	(MMC_CAP2_PACKED_RD | \
 				 MMC_CAP2_PACKED_WR)
 #define MMC_CAP2_NO_PRESCAN_POWERUP (1 << 14)	/* Don't power up before scan */
+#define MMC_CAP2_NO_MMC		(1 << 15)	/* Only SD supported, not MMC */
 
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */
 
-- 
1.7.10.4

Re: [PATCH] mmc: core: Add a capability for disabling mmc cards

[Adam Lee]

On Tue, May 14, 2013 at 03:38:17PM +0800, Adam Lee wrote:
> On some systems we need a way to disable MMC card support in a MMC/SD
> card slot due to the legal concern.
> 
> Add support in the core SD/MMC code to support this.

CC more addresses.

Yes, this capability seems odd, but linux computer vendors need this to
avoid legal problems. Please review, thanks.

-- 
Regards,
Adam Lee
Hardware Enablement

Re: [PATCH] mmc: core: Add a capability for disabling mmc cards

[Linus Walleij]

On Tue, May 14, 2013 at 9:38 AM, Adam Lee <adam.lee@canonical.com> wrote:

> On some systems we need a way to disable MMC card support in a MMC/SD
> card slot due to the legal concern.
>
> Add support in the core SD/MMC code to support this.
>
> Signed-off-by: Doug Anderson <dianders@chromium.org>
> Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
> Signed-off-by: Adam Lee <adam.lee@canonical.com>

(...)
>  #define MMC_CAP2_NO_PRESCAN_POWERUP (1 << 14)  /* Don't power up before scan */
> +#define MMC_CAP2_NO_MMC                (1 << 15)       /* Only SD supported, not MMC */

I would name that MMC_CAP2_DISABLE_MMC_BUT_NOT_SD
because that is what it means.

People wanting to set that capability for said legal reasons
will not read the git log.

So also encode what you just said in the comment for the CAP
so it is crystal clear what this is for.

I'm a bit ambivalent about what kind of benefits this provides
to human users of the Linux kernel, while I do understand the
benefit it provides for legal bodies...

Yours,
Linus Walleij

Re: [PATCH] mmc: core: Add a capability for disabling mmc cards

[Chris Ball]

Hi,

On Tue, May 14 2013, Adam Lee wrote:
> On Tue, May 14, 2013 at 03:38:17PM +0800, Adam Lee wrote:
>> On some systems we need a way to disable MMC card support in a MMC/SD
>> card slot due to the legal concern.
>> 
>> Add support in the core SD/MMC code to support this.
>
> CC more addresses.
>
> Yes, this capability seems odd, but linux computer vendors need this to
> avoid legal problems. Please review, thanks.

This has already been NACKed by Nicolas:

https://patchwork.kernel.org/patch/1359121/

(At least, I think it has -- your forward doesn't include the patch
itself.)

Thanks,

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child

Re: [PATCH] mmc: core: Add a capability for disabling mmc cards

[Doug Anderson]

Chris / Adam,

On Tue, May 14, 2013 at 4:19 AM, Chris Ball <cjb@laptop.org> wrote:
> This has already been NACKed by Nicolas:
>
> https://patchwork.kernel.org/patch/1359121/
>
> (At least, I think it has -- your forward doesn't include the patch
> itself.)

Yup, it got NAKed.  Unless something has changed I think that
interested parties will need to carry this as a local patch.

-Doug

Re: [PATCH] mmc: core: Add a capability for disabling mmc cards

[Nicolas Pitre]

On Tue, 14 May 2013, Chris Ball wrote:

> Hi,
> 
> On Tue, May 14 2013, Adam Lee wrote:
> > On Tue, May 14, 2013 at 03:38:17PM +0800, Adam Lee wrote:
> >> On some systems we need a way to disable MMC card support in a MMC/SD
> >> card slot due to the legal concern.
> >> 
> >> Add support in the core SD/MMC code to support this.
> >
> > CC more addresses.
> >
> > Yes, this capability seems odd, but linux computer vendors need this to
> > avoid legal problems. Please review, thanks.
> 
> This has already been NACKed by Nicolas:
> 
> https://patchwork.kernel.org/patch/1359121/
> 
> (At least, I think it has -- your forward doesn't include the patch
> itself.)

I certainly did.  Technical amputations driven by legal stupidities 
don't belong in the mainline kernel.


Nicolas