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Thu, 30 Jul 2026 22:39:07 -0700 (PDT) Date: Fri, 31 Jul 2026 11:09:01 +0530 From: Mohamad Raizudeen To: bhelgaas@google.com Cc: alex@shazbot.org, skhan@linuxfoundation.org, jkoolstra@xs4all.nl, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] PCI: Fix 32-bit config write in Intel RP MPC ACS quirk Message-ID: References: <20260723171203.4892-1-raizudeen.kerneldev@gmail.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260723171203.4892-1-raizudeen.kerneldev@gmail.com> On Thu, Jul 23, 2026 at 10:42:03PM +0530, Mohamad Raizudeen wrote: > The pci_quirk_enable_intel_rp_mpc_acs() reads a 32 bit DWORD from the > MPC register, sets bit 26 (INTEL_MPC_REG_IRBNCE), but it writes it back > using pci_write_config_word(). > > Because bit 26 resides in the upper 16 bits of the 32 bit register, a 16 > bit write to offset 0xd8 completely drops the newly set bit. The quirk > logs that it is enabling IRBNCE, but the hardware never actually > receives the command. > > Fix this by using pci_write_config_dword() to ensure the full 32 bit > value is written back to the hardware. > > Fixes: d99321b63b1f ("PCI: Enable quirks for PCIe ACS on Intel PCH root ports") > Signed-off-by: Mohamad Raizudeen > --- > Changes in v2: > - Added "Fixes:" tag and CC'd Alex Williamson as requested by Bjorn Helgaas. > > Link to v1: https://lore.kernel.org/linux-pci/20260723160641.GC836122@bhelgaas/T/#t > > drivers/pci/quirks.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c > index b09f27f7846f..0d0cf6f86173 100644 > --- a/drivers/pci/quirks.c > +++ b/drivers/pci/quirks.c > @@ -5361,7 +5361,7 @@ static void pci_quirk_enable_intel_rp_mpc_acs(struct pci_dev *dev) > if (!(mpc & INTEL_MPC_REG_IRBNCE)) { > pci_info(dev, "Enabling MPC IRBNCE\n"); > mpc |= INTEL_MPC_REG_IRBNCE; > - pci_write_config_word(dev, INTEL_MPC_REG, mpc); > + pci_write_config_dword(dev, INTEL_MPC_REG, mpc); > } > } > > -- > 2.53.0 > Hi Bjorn, Just following up on this v2 patch. Please let me know if you have any feedback or if further changes are needed. Thanks & regards, Mohamad Raizudeen