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c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1791477690; bh=RrdGR8+5+7JD9zLubC3R5Nrwx3f6rQnHI7MHAeeFjZE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iEZgnBHlg1T1yn8CZKhtuBx45f1+HQol4iZG3iM7TQiQXiFIlmf21T9mvH4xgbgRy qUB/J1fkHFphCRL55R8CWqDa4i5ZPlrg3EWE4PLqdRgqrJtOfmoZ39QDPhyiFLR0uK JIx2GA3l12I4vaoXbAFUVMUa5oGTMjpbEw8yJcIw= From: Easwar Hariharan To: jeffbarnes@linux.microsoft.com Cc: Frank.li@oss.nxp.com, Zhiqiang.Hou@nxp.com, bhelgaas@google.com, imx@lists.linux.dev, kwilczynski@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, lpieralisi@kernel.org, mani@kernel.org, minghuan.Lian@nxp.com, mingkai.hu@nxp.com, robh@kernel.org, roy.zang@nxp.com, Easwar Hariharan Subject: [PATCH v2] Revert "PCI: layerscape: Change default error response behavior" Date: Thu, 8 Oct 2026 16:42:02 +0000 Message-ID: <20261008164202.64477-1-easwar.hariharan@linux.microsoft.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261001153323.1965074-1-jeffbarnes@linux.microsoft.com> References: <20261001153323.1965074-1-jeffbarnes@linux.microsoft.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit > This reverts commit 84d897d69938 > ("PCI: layerscape: Change default error response behavior"). > > The Layerscape PCIe driver programs the DesignWare > AMBA_ERROR_RESPONSE_DEFAULT register at offset 0x8d0 with 0x9401. > > For AXI, the documented default with AMBA_ERROR_RESPONSE_GLOBAL cleared > returns OKAY with all-ones data for errors on non-posted requests. > Setting AMBA_ERROR_RESPONSE_GLOBAL causes an AXI error response instead, > with AMBA_ERROR_RESPONSE_MAP selecting SLVERR or DECERR for individual > PCIe completion errors. > > The value 0x9401 sets AMBA_ERROR_RESPONSE_GLOBAL and maps Unsupported > Request, Completer Abort, and Completion Timeout to SLVERR. > > A PCI configuration access can race with the link going down after > dw_pcie_other_conf_map_bus() checks the link but before > pci_generic_config_read() performs the MMIO access. If the transaction > results in a Completion Timeout, the Layerscape error response setting > propagates it to AXI as SLVERR, resulting in an asynchronous SError and > kernel panic. > Could you bring back the kernel panic backtrace from v1? With that, Reviewed-by: Easwar Hariharan > Reproduce the race by obtaining the configuration-space mapping while > the link is up, then disabling the link from another CPU immediately > before performing the MMIO configuration read. > > With the error response override enabled, the overlapping configuration > read results in an asynchronous SError and kernel panic. With the > DesignWare default behavior restored, the same test returns 0xffffffff. > AER reports a non-fatal Completion Timeout, and no SError or kernel > panic occurs. > > Restore the documented DesignWare default error response behavior so a > failed non-posted PCIe transaction does not become a fatal AXI error. > > Fixes: 84d897d69938 ("PCI: layerscape: Change default error response behavior") > Cc: stable@vger.kernel.org > Signed-off-by: Jeff Barnes > > Changes in v2: > - Change the subject to identify this as a revert, as requested by > Frank Li. > - Document the DesignWare AMBA_ERROR_RESPONSE_DEFAULT behavior and > decode the 0x9401 setting used by Layerscape. > - Clarify that the setting propagates Completion Timeout as AXI SLVERR > rather than causing the underlying PCIe transaction failure. > > --- > drivers/pci/controller/dwc/pci-layerscape.c | 12 ------------ > 1 file changed, 12 deletions(-)