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Mon, 15 Jun 2026 23:06:04 -0700 (PDT) Received: from [172.20.10.3] ([37.167.70.197]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922fa891acsm51925935e9.9.2026.06.15.23.06.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Jun 2026 23:06:04 -0700 (PDT) Message-ID: Date: Tue, 16 Jun 2026 08:06:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: neil.armstrong@linaro.org Subject: Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable To: Ronald Claveau , Gowtham Kudupudi Cc: robh@kernel.org, bhelgaas@google.com, khilman@baylibre.com, jbrunet@baylibre.com, martin.blumenstingl@googlemail.com, linux-pci@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, yue.wang@Amlogic.com, lpieralisi@kernel.org, kwilczynski@kernel.org, mani@kernel.org References: <20260614015620.20432-1-gowtham@ferryfair.com> <84cc8b0c-da06-4d01-a076-9743c29c91f6@aliel.fr> Content-Language: en-US, fr Autocrypt: addr=neil.armstrong@linaro.org; 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charset="us-ascii"; Format="flowed" Sender: "linux-amlogic" Errors-To: linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org 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 >> --- >> 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 >> >> 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 > _______________________________________________ linux-amlogic mailing list linux-amlogic@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-amlogic