[PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[Gowtham Kudupudi]

On warm reboot, the PCIe controller's LTSSM starts link training
immediately if PERST# is already deasserted from the previous boot.
The driver then pulses PERST# for only 500us, which is too short to
properly reset the endpoint device that has already started training.

Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
so the endpoint gets a clean reset cycle before link training begins.

This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
Cold boot worked because POR held PERST# low; warm reboot did not.
The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.

Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
---
 drivers/pci/controller/dwc/pci-meson.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 5f8e2f4b3c12..3a7e9f1d5b8c 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -310,8 +310,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
 {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
+	meson_pcie_assert_reset(mp);
 	meson_pcie_ltssm_enable(mp);
-	meson_pcie_assert_reset(mp);
 
 	return 0;
 }
-- 
2.49.0

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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[sashiko-bot]

> On warm reboot, the PCIe controller's LTSSM starts link training
> immediately if PERST# is already deasserted from the previous boot.
> The driver then pulses PERST# for only 500us, which is too short to
> properly reset the endpoint device that has already started training.
> 
> Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
> so the endpoint gets a clean reset cycle before link training begins.
> 
> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> Cold boot worked because POR held PERST# low; warm reboot did not.
> The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.
> 
> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260614015620.20432-1-gowtham@ferryfair.com?part=1


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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[Ronald Claveau]

On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:
> On warm reboot, the PCIe controller's LTSSM starts link training
> immediately if PERST# is already deasserted from the previous boot.
> The driver then pulses PERST# for only 500us, which is too short to
> properly reset the endpoint device that has already started training.
> 
> Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
> so the endpoint gets a clean reset cycle before link training begins.
> 
> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> Cold boot worked because POR held PERST# low; warm reboot did not.
> The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.
> 
> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
> ---
>  drivers/pci/controller/dwc/pci-meson.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
> index 5f8e2f4b3c12..3a7e9f1d5b8c 100644
> --- a/drivers/pci/controller/dwc/pci-meson.c
> +++ b/drivers/pci/controller/dwc/pci-meson.c
> @@ -310,8 +310,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
>  {
>  	struct meson_pcie *mp = to_meson_pcie(pci);
>  
> +	meson_pcie_assert_reset(mp);
>  	meson_pcie_ltssm_enable(mp);
> -	meson_pcie_assert_reset(mp);
>  
>  	return 0;
>  }

Hi Gowtham,

I have a patch [1] that I haven't submitted yet.
This might be related to your issue, what do you think ?

[1] https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756

-- 
Best regards,
Ronald

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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[neil.armstrong]

On 6/15/26 12:34, Ronald Claveau wrote:
> On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:
>> On warm reboot, the PCIe controller's LTSSM starts link training
>> immediately if PERST# is already deasserted from the previous boot.
>> The driver then pulses PERST# for only 500us, which is too short to
>> properly reset the endpoint device that has already started training.
>>
>> Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
>> so the endpoint gets a clean reset cycle before link training begins.
>>
>> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
>> Cold boot worked because POR held PERST# low; warm reboot did not.
>> The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.
>>
>> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
>> ---
>>   drivers/pci/controller/dwc/pci-meson.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
>> index 5f8e2f4b3c12..3a7e9f1d5b8c 100644
>> --- a/drivers/pci/controller/dwc/pci-meson.c
>> +++ b/drivers/pci/controller/dwc/pci-meson.c
>> @@ -310,8 +310,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
>>   {
>>   	struct meson_pcie *mp = to_meson_pcie(pci);
>>   
>> +	meson_pcie_assert_reset(mp);
>>   	meson_pcie_ltssm_enable(mp);
>> -	meson_pcie_assert_reset(mp);

I think this change is valid, other controllers resets PERST
in the host init callback, so either this or move to the
init callback.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

>>   
>>   	return 0;
>>   }
> 
> Hi Gowtham,
> 
> I have a patch [1] that I haven't submitted yet.
> This might be related to your issue, what do you think ?

Ronald, This fix is valid, it's definitely better to probe the
driver with PERST asserted, please send it.

Neil

> 
> [1] https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756
> 


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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[gowtham]

Hi,

As Neil suggested I moved the PCIe reset to init; I've updated the tag
at
https://github.com/GowthamKudupudi/linux/tree/meson-pcie-warm-reset-linux-7.0.y

Ronald, yes, I do think its proper to initialize PCIe with RESET Active.
Anyway we need the reset *cycle*. Please submit your patch as well.

Thank you!

...Gowtham

On Tue, 16 Jun 2026 08:06:02 +0200
neil.armstrong@linaro.org wrote:

> On 6/15/26 12:34, Ronald Claveau wrote:
> > On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:  
> >> On warm reboot, the PCIe controller's LTSSM starts link training
> >> immediately if PERST# is already deasserted from the previous boot.
> >> The driver then pulses PERST# for only 500us, which is too short to
> >> properly reset the endpoint device that has already started
> >> training.
> >>
> >> Fix by moving the PERST# assert/deassert pulse BEFORE enabling
> >> LTSSM, so the endpoint gets a clean reset cycle before link
> >> training begins.
> >>
> >> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> >> Cold boot worked because POR held PERST# low; warm reboot did not.
> >> The fix was confirmed on a Banana Pi CM4 with Waveshare IO base
> >> board.
> >>
> >> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
> >> ---
> >>   drivers/pci/controller/dwc/pci-meson.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/pci/controller/dwc/pci-meson.c
> >> b/drivers/pci/controller/dwc/pci-meson.c index
> >> 5f8e2f4b3c12..3a7e9f1d5b8c 100644 ---
> >> a/drivers/pci/controller/dwc/pci-meson.c +++
> >> b/drivers/pci/controller/dwc/pci-meson.c @@ -310,8 +310,8 @@
> >> static int meson_pcie_start_link(struct dw_pcie *pci) {
> >>   	struct meson_pcie *mp = to_meson_pcie(pci);
> >>   
> >> +	meson_pcie_assert_reset(mp);
> >>   	meson_pcie_ltssm_enable(mp);
> >> -	meson_pcie_assert_reset(mp);  
> 
> I think this change is valid, other controllers resets PERST
> in the host init callback, so either this or move to the
> init callback.
> 
> Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
> 
> >>   
> >>   	return 0;
> >>   }  
> > 
> > Hi Gowtham,
> > 
> > I have a patch [1] that I haven't submitted yet.
> > This might be related to your issue, what do you think ?  
> 
> Ronald, This fix is valid, it's definitely better to probe the
> driver with PERST asserted, please send it.
> 
> Neil
> 
> > 
> > [1]
> > https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756 
> 


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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[gowtham]

[-- Attachment #1: Type: text/plain, Size: 4506 bytes --]

Hi Ronald,
I see you submitted the patch. Last couple of days I've been fixing the
etherenet of my BPiCM4+Waveshare-io-base-b due to which I couldn't test
your patch any sooner. Now I got my ethernet working but now I couldn't
reproduce the issue *without* either of our patches!!!

Anyway it's proper to initialize PCIe with RESET Active but I think
meson_pcie_assert_reset(mp) will give sufficient time to PCIe devices
to complete the reset cycle.

---
 drivers/pci/controller/dwc/pci-meson.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c
b/drivers/pci/controller/dwc/pci-meson.c index 0694084f612..c28ab40c9ff
100644 --- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,8 +308,8 @@ static int meson_pcie_start_link(struct dw_pcie
*pci) {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_ltssm_enable(mp);
 	meson_pcie_assert_reset(mp);
+	meson_pcie_ltssm_enable(mp);
 
 	return 0;
 }
-- 
---
 drivers/pci/controller/dwc/pci-meson.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c
b/drivers/pci/controller/dwc/pci-meson.c index c28ab40c9ff..2ef75157530
100644 --- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,7 +308,6 @@ static int meson_pcie_start_link(struct dw_pcie
*pci) {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_assert_reset(mp);
 	meson_pcie_ltssm_enable(mp);
 
 	return 0;
@@ -362,6 +361,8 @@ static int meson_pcie_host_init(struct dw_pcie_rp
*pp) 
 	pp->bridge->ops = &meson_pci_ops;
 
+	meson_pcie_assert_reset(mp);
+
 	meson_set_max_payload(mp, MAX_PAYLOAD_SIZE);
 	meson_set_max_rd_req_size(mp, MAX_READ_REQ_SIZE);
 
-- 

...Gowtham


On Wed, 17 Jun 2026 05:06:27 +0530
gowtham <gowtham@ferryfair.com> wrote:

> Hi,
> 
> As Neil suggested I moved the PCIe reset to init; I've updated the tag
> at
> https://github.com/GowthamKudupudi/linux/tree/meson-pcie-warm-reset-linux-7.0.y
> 
> Ronald, yes, I do think its proper to initialize PCIe with RESET
> Active. Anyway we need the reset *cycle*. Please submit your patch as
> well.
> 
> Thank you!
> 
> ...Gowtham
> 
> On Tue, 16 Jun 2026 08:06:02 +0200
> neil.armstrong@linaro.org wrote:
> 
> > On 6/15/26 12:34, Ronald Claveau wrote:  
> > > On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:    
> > >> On warm reboot, the PCIe controller's LTSSM starts link training
> > >> immediately if PERST# is already deasserted from the previous
> > >> boot. The driver then pulses PERST# for only 500us, which is too
> > >> short to properly reset the endpoint device that has already
> > >> started training.
> > >>
> > >> Fix by moving the PERST# assert/deassert pulse BEFORE enabling
> > >> LTSSM, so the endpoint gets a clean reset cycle before link
> > >> training begins.
> > >>
> > >> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> > >> Cold boot worked because POR held PERST# low; warm reboot did
> > >> not. The fix was confirmed on a Banana Pi CM4 with Waveshare IO
> > >> base board.
> > >>
> > >> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
> > >> ---
> > >>   drivers/pci/controller/dwc/pci-meson.c | 2 +-
> > >>   1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/pci/controller/dwc/pci-meson.c
> > >> b/drivers/pci/controller/dwc/pci-meson.c index
> > >> 5f8e2f4b3c12..3a7e9f1d5b8c 100644 ---
> > >> a/drivers/pci/controller/dwc/pci-meson.c +++
> > >> b/drivers/pci/controller/dwc/pci-meson.c @@ -310,8 +310,8 @@
> > >> static int meson_pcie_start_link(struct dw_pcie *pci) {
> > >>   	struct meson_pcie *mp = to_meson_pcie(pci);
> > >>   
> > >> +	meson_pcie_assert_reset(mp);
> > >>   	meson_pcie_ltssm_enable(mp);
> > >> -	meson_pcie_assert_reset(mp);    
> > 
> > I think this change is valid, other controllers resets PERST
> > in the host init callback, so either this or move to the
> > init callback.
> > 
> > Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
> >   
> > >>   
> > >>   	return 0;
> > >>   }    
> > > 
> > > Hi Gowtham,
> > > 
> > > I have a patch [1] that I haven't submitted yet.
> > > This might be related to your issue, what do you think ?    
> > 
> > Ronald, This fix is valid, it's definitely better to probe the
> > driver with PERST asserted, please send it.
> > 
> > Neil
> >   
> > > 
> > > [1]
> > > https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756
> > >   
> >   
> 


[-- Attachment #2: 0001-PCI-meson-Fix-PERST-timing-by-asserting-reset-before.patch --]
[-- Type: text/x-patch, Size: 1488 bytes --]

From 852811b11795ee389ea6a953ed0db69b76722469 Mon Sep 17 00:00:00 2001
From: Gowtham Kudupudi <gowtham@ferryfair.com>
Date: Sun, 14 Jun 2026 09:41:01 +0530
Subject: [PATCH 1/2] PCI: meson: Fix PERST# timing by asserting reset before
 LTSSM enable

On warm reboot, the PCIe controller's LTSSM starts link training
immediately if PERST# is already deasserted from the previous boot.
The driver then pulses PERST# for only 500us, which is too short to
properly reset the endpoint device that has already started training.

Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
so the endpoint gets a clean reset cycle before link training begins.

This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
Cold boot worked because POR held PERST# low; warm reboot did not.
The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.

Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
---
 drivers/pci/controller/dwc/pci-meson.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 0694084f612..c28ab40c9ff 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,8 +308,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
 {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_ltssm_enable(mp);
 	meson_pcie_assert_reset(mp);
+	meson_pcie_ltssm_enable(mp);
 
 	return 0;
 }
-- 
2.54.0


[-- Attachment #3: 0002-PCI-meson-pcie-reset-moved-to-meson_pcie_host_init.patch --]
[-- Type: text/x-patch, Size: 1159 bytes --]

From 1bcf2c787d72b2c25852cc598b1201510b4132b0 Mon Sep 17 00:00:00 2001
From: Gowtham Kudupudi <gowtham@ferryfair.com>
Date: Wed, 17 Jun 2026 04:29:45 +0530
Subject: [PATCH 2/2] PCI: meson: pcie reset moved to meson_pcie_host_init

As per the Neil's suggestion, inititial PCIe reset is moved to init
to make it proper.

Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
---
 drivers/pci/controller/dwc/pci-meson.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index c28ab40c9ff..2ef75157530 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,7 +308,6 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
 {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_assert_reset(mp);
 	meson_pcie_ltssm_enable(mp);
 
 	return 0;
@@ -362,6 +361,8 @@ static int meson_pcie_host_init(struct dw_pcie_rp *pp)
 
 	pp->bridge->ops = &meson_pci_ops;
 
+	meson_pcie_assert_reset(mp);
+
 	meson_set_max_payload(mp, MAX_PAYLOAD_SIZE);
 	meson_set_max_rd_req_size(mp, MAX_READ_REQ_SIZE);
 
-- 
2.54.0


[-- Attachment #4: Type: text/plain, Size: 167 bytes --]

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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[Ronald Claveau]

On 6/17/26 10:30 PM, gowtham wrote:
> Hi Ronald,
> I see you submitted the patch. Last couple of days I've been fixing the
> etherenet of my BPiCM4+Waveshare-io-base-b due to which I couldn't test
> your patch any sooner. Now I got my ethernet working but now I couldn't
> reproduce the issue *without* either of our patches!!!
> 
> Anyway it's proper to initialize PCIe with RESET Active but I think
> meson_pcie_assert_reset(mp) will give sufficient time to PCIe devices
> to complete the reset cycle.
> 

Hi Gowtham,

No worries and no rush to me.
I think it's due to how uboot set the gpio before the linux boot for my
issue, and that does not seem to be relevant for yours.
Thank you for testing the patch.

> ---
>  drivers/pci/controller/dwc/pci-meson.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-meson.c
> b/drivers/pci/controller/dwc/pci-meson.c index 0694084f612..c28ab40c9ff
> 100644 --- a/drivers/pci/controller/dwc/pci-meson.c
> +++ b/drivers/pci/controller/dwc/pci-meson.c
> @@ -308,8 +308,8 @@ static int meson_pcie_start_link(struct dw_pcie
> *pci) {
>  	struct meson_pcie *mp = to_meson_pcie(pci);
>  
> -	meson_pcie_ltssm_enable(mp);
>  	meson_pcie_assert_reset(mp);
> +	meson_pcie_ltssm_enable(mp);
>  
>  	return 0;
>  }


-- 
Best regards,
Ronald

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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[Manivannan Sadhasivam]

On Mon, Jun 15, 2026 at 12:34:11PM +0200, Ronald Claveau wrote:
> On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:
> > On warm reboot, the PCIe controller's LTSSM starts link training
> > immediately if PERST# is already deasserted from the previous boot.
> > The driver then pulses PERST# for only 500us, which is too short to
> > properly reset the endpoint device that has already started training.
> > 
> > Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
> > so the endpoint gets a clean reset cycle before link training begins.
> > 
> > This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> > Cold boot worked because POR held PERST# low; warm reboot did not.
> > The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.
> > 
> > Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
> > ---
> >  drivers/pci/controller/dwc/pci-meson.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
> > index 5f8e2f4b3c12..3a7e9f1d5b8c 100644
> > --- a/drivers/pci/controller/dwc/pci-meson.c
> > +++ b/drivers/pci/controller/dwc/pci-meson.c
> > @@ -310,8 +310,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
> >  {
> >  	struct meson_pcie *mp = to_meson_pcie(pci);
> >  
> > +	meson_pcie_assert_reset(mp);
> >  	meson_pcie_ltssm_enable(mp);
> > -	meson_pcie_assert_reset(mp);

meson_pcie_assert_reset() itself is wrong as it toggles PERST#. You'd just need:

msleep(PCIE_T_PERST_CLK_US);
gpiod_set_value_cansleep(mp->reset_gpio, GPIOD_OUT_LOW)

but in probe(), after meson_pcie_probe_clocks() as that's when both power and
REFCLK becomes stable.

> >  
> >  	return 0;
> >  }
> 
> Hi Gowtham,
> 
> I have a patch [1] that I haven't submitted yet.
> This might be related to your issue, what do you think ?
> 
> [1] https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756
> 

This patch is also needed as it correctly fixes the PERST# polarity when
requesting the GPIO. Since the devicetree is defining the PERST# GPIO as
ACIVE_LOW, the driver should request it as GPIOD_OUT_HIGH to make sure that
PERST# is asserted.

So please submit the referenced patch.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

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Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

[Ronald Claveau]

On 6/20/26 5:11 PM, Manivannan Sadhasivam wrote:
> On Mon, Jun 15, 2026 at 12:34:11PM +0200, Ronald Claveau wrote:
>> On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:
>>> On warm reboot, the PCIe controller's LTSSM starts link training
>>> immediately if PERST# is already deasserted from the previous boot.
>>> The driver then pulses PERST# for only 500us, which is too short to
>>> properly reset the endpoint device that has already started training.
>>>
>>> Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
>>> so the endpoint gets a clean reset cycle before link training begins.
>>>
>>> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
>>> Cold boot worked because POR held PERST# low; warm reboot did not.
>>> The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.
>>>
>>> Signed-off-by: Gowtham Kudupudi <gowtham@ferryfair.com>
>>> ---
>>>  drivers/pci/controller/dwc/pci-meson.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
>>> index 5f8e2f4b3c12..3a7e9f1d5b8c 100644
>>> --- a/drivers/pci/controller/dwc/pci-meson.c
>>> +++ b/drivers/pci/controller/dwc/pci-meson.c
>>> @@ -310,8 +310,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
>>>  {
>>>  	struct meson_pcie *mp = to_meson_pcie(pci);
>>>  
>>> +	meson_pcie_assert_reset(mp);
>>>  	meson_pcie_ltssm_enable(mp);
>>> -	meson_pcie_assert_reset(mp);
> 
> meson_pcie_assert_reset() itself is wrong as it toggles PERST#. You'd just need:
> 
> msleep(PCIE_T_PERST_CLK_US);
> gpiod_set_value_cansleep(mp->reset_gpio, GPIOD_OUT_LOW)
> 
> but in probe(), after meson_pcie_probe_clocks() as that's when both power and
> REFCLK becomes stable.
> 
>>>  
>>>  	return 0;
>>>  }
>>
>> Hi Gowtham,
>>
>> I have a patch [1] that I haven't submitted yet.
>> This might be related to your issue, what do you think ?
>>
>> [1] https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756
>>
> 
> This patch is also needed as it correctly fixes the PERST# polarity when
> requesting the GPIO. Since the devicetree is defining the PERST# GPIO as
> ACIVE_LOW, the driver should request it as GPIOD_OUT_HIGH to make sure that
> PERST# is asserted.
> 
> So please submit the referenced patch.
> 
> - Mani
> 

Hi Mani,

I sent it here:

https://lore.kernel.org/all/20260616-fix-meson-pcie-reset-gpio-v1-1-fca404b4c8be@aliel.fr/


-- 
Best regards,
Ronald

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