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@xxxxxxxxxxxxx>
>>> ---
>>>  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@xxxxxxxx/


-- 
Best regards,
Ronald