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Tue, 16 Jun 2026 16:31:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781627496; bh=rfOBWu4WGt30uIecGlCElGeir0L2JNoVF0lc9QokdN8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=U/MOK4O67K2skWmmisnBHBY2zXyU2PEUqFqnMpM3Ssx/4ta+m1Z64wnKK20cj7xSx zoGibbH8IrTbIqXUXh/CoULhJRb6+2U42n08leeoyCgsRgSqHT3XYOX2FJh36iQEpx SaXwoV2yCASCywmxxilxS/4cmUD3sB/PkJtP2z0hNqeZyjdJiIfxdmORa80a/2zb6M Xj8vwybQcgHTuGSR9e93u5KkOXOsTOkW0zTVgUi9JVia4FjORIZOclxSa1vSt5DTws BFHMYnUHcK9AZeEVMW8fC1SPJOS1TTV/cVjt6PNBwXAIY1qk/yx9dFXhOL8QepIyIn mJhvf+DlTMa2w== From: =?UTF-8?q?Krzysztof=20Wilczy=C5=84ski?= To: Madhavan Srinivasan , Bjorn Helgaas , Michael Ellerman Cc: Bjorn Helgaas , Nicholas Piggin , Christophe Leroy , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , Kees Cook , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: [PATCH 2/2] PCI/sysfs: Fix read byte order in pci_read_legacy_io() Date: Tue, 16 Jun 2026 16:31:31 +0000 Message-ID: <20260616163131.2763281-2-kwilczynski@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616163131.2763281-1-kwilczynski@kernel.org> References: <20260616163131.2763281-1-kwilczynski@kernel.org> 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 pci_read_legacy_io() passes the sysfs buffer directly to pci_legacy_read(): return pci_legacy_read(bus, off, (u32 *)buf, count); The PowerPC implementation stores the result as a native-endian integer: *((u16 *)val) = in_le16(addr); On big-endian PowerPC this stores the bytes in the wrong order, so a 2-byte read of a device register returns different bytes than two 1-byte reads at the same addresses. The same applies to 4-byte reads. On little-endian the native byte order already matches PCI I/O port byte order, so the conversion is a no-op. Thus, let pci_legacy_read() store into a local u32 variable, then copy the I/O port value to the sysfs buffer using put_unaligned_le16() and put_unaligned_le32() for the 2 and 4 byte cases, converting from the native integer to little-endian byte order matching PCI I/O port space. No changes are needed for the Alpha platform. The legacy_io file is root-only and exists only on Alpha and PowerPC, the two architectures that define HAVE_PCI_LEGACY. Cc: stable@vger.kernel.org Signed-off-by: Krzysztof Wilczyński --- drivers/pci/pci-sysfs.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c index b56000ba3a33..2354d09fd3fa 100644 --- a/drivers/pci/pci-sysfs.c +++ b/drivers/pci/pci-sysfs.c @@ -908,12 +908,30 @@ static ssize_t pci_read_legacy_io(struct file *filp, struct kobject *kobj, char *buf, loff_t off, size_t count) { struct pci_bus *bus = to_pci_bus(kobj_to_dev(kobj)); + u32 val = 0; + int ret; /* Only support 1, 2 or 4 byte accesses */ if (count != 1 && count != 2 && count != 4) return -EINVAL; - return pci_legacy_read(bus, off, (u32 *)buf, count); + ret = pci_legacy_read(bus, off, &val, count); + if (ret < 0) + return ret; + + switch (count) { + case 1: + buf[0] = *(u8 *)&val; + break; + case 2: + put_unaligned_le16(*(u16 *)&val, buf); + break; + case 4: + put_unaligned_le32(val, buf); + break; + } + + return ret; } /** -- 2.54.0