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@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);

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@xxxxxxxxxx>

> >   
> >   	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