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

[gowtham <gowtham@ferryfair.com>]

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 
>