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

[Ronald Claveau <linux-kernel-dev@aliel.fr>]

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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