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[72.194.116.95]) by smtp.gmail.com with ESMTPSA id y4-20020a0cd984000000b006262e5c96d0sm2166245qvj.129.2023.08.06.08.15.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 06 Aug 2023 08:16:00 -0700 (PDT) Message-ID: <7f6a7a38-8683-7275-d3ee-24a4cd06f8a6@broadcom.com> Date: Sun, 6 Aug 2023 08:15:57 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] PCI: brcmstb: Avoid downstream access during link training To: Lukas Wunner , Jim Quinlan , Nicolas Saenz Julienne , Lorenzo Pieralisi , Krzysztof Wilczynski , Rob Herring , Bjorn Helgaas , Jim Quinlan Cc: bcm-kernel-feedback-list@broadcom.com, linux-pci@vger.kernel.org, Philipp Rosenberger , Cyril Brulebois References: <385baf9dbfb6b65112803998dfc0cd6f84a5e6ba.1691296765.git.lukas@wunner.de> From: Florian Fainelli In-Reply-To: <385baf9dbfb6b65112803998dfc0cd6f84a5e6ba.1691296765.git.lukas@wunner.de> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="000000000000c06dee0602429bda" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org --000000000000c06dee0602429bda Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/5/2023 9:44 PM, Lukas Wunner wrote: > The Broadcom Set Top Box PCIe controller signals an Asynchronous SError > Interrupt and thus causes a kernel panic when non-posted transactions > time out. This differs from most other PCIe controllers which return a > fabricated "all ones" response instead. > > To avoid gratuitous kernel panics, the driver reads the link status from > a proprietary PCIE_MISC_PCIE_STATUS register and skips downstream > accesses if the link is down. > > However the bits in the proprietary register may purport that the link > is up even though link training is still in progress (as indicated by > the Link Training bit in the Link Status register). > > This has been observed with various PCIe switches attached to a BCM2711 > (Raspberry Pi CM4): The issue is most pronounced with the Pericom > PI7C9X2G404SV, but has also occasionally been witnessed with the Pericom > PI7C9X2G404SL and ASMedia ASM1184e. > > Check the Link Training bit in addition to the PCIE_MISC_PCIE_STATUS > register before performing downstream accesses. > > Signed-off-by: Lukas Wunner > Cc: Since you CC stable, it would be neat to provide a Fixes: tag here, most likely this dates back from the original commit adding support for this driver. > --- > drivers/pci/controller/pcie-brcmstb.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c > index f593a422bd63..b4abfced8e9b 100644 > --- a/drivers/pci/controller/pcie-brcmstb.c > +++ b/drivers/pci/controller/pcie-brcmstb.c > @@ -679,8 +679,10 @@ static bool brcm_pcie_link_up(struct brcm_pcie *pcie) > u32 val = readl(pcie->base + PCIE_MISC_PCIE_STATUS); > u32 dla = FIELD_GET(PCIE_MISC_PCIE_STATUS_PCIE_DL_ACTIVE_MASK, val); > u32 plu = FIELD_GET(PCIE_MISC_PCIE_STATUS_PCIE_PHYLINKUP_MASK, val); > + u16 lnksta = readw(pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKSTA); > + u16 lt = FIELD_GET(PCI_EXP_LNKSTA_LT, lnksta); > > - return dla && plu; > + return dla && plu && !lt; The patch looks good to me in spirit though I want Jim to review and provide feedback here since he was looking at this sort of issues not so long ago. 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