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[34.142.211.105]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc7a4b03082sm2784007a12.11.2026.09.28.10.19.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Sep 2026 10:19:07 -0700 (PDT) Date: Mon, 28 Sep 2026 17:18:58 +0000 From: Pranjal Shrivastava To: David Matlack Cc: kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Rientjes , Jacob Pan , Jason Gunthorpe , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pratyush Yadav , Randy Dunlap , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Vipin Sharma , William Tu , Yi Liu Subject: Re: [PATCH v9 08/13] PCI: Save and restore the ACS Control register Message-ID: References: <20260918200640.887030-1-dmatlack@google.com> <20260918200640.887030-9-dmatlack@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260918200640.887030-9-dmatlack@google.com> X-Stat-Signature: eeamah595pemnuapy3a7ifnm3xiycnxs X-Rspamd-Queue-Id: 35AAF10000D X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1790615950-32224 X-HE-Meta: U2FsdGVkX1+9rVRFQa5iQO+GmR6B8WCFin9tvIxuxGqPcwhDsD3EOIDF5pdwzdj2dUQIpJTnBRqcJsEs0g7r951dtxIC4Y7oQV/ohGRELI3QTLwdRwpzyyUltrF8M7WIcCIk8sGqZXTHAmsS4i1KEI2riaIN/zimpM84+ssYRO3NuqUOIlEvfWg6d1xozy3ycd0y4bM1fxpnFWx+XkmwH1xyEpUbrxcro0DpefsdkTHSRnvQPeAMSaZp490IQsnXEBpyCcbWTz5lduV0gP0wgOEh9vAoXR9XOKIwbHIyWTWB62eDmLfhv5XD8qAM5U/RN/lkFZ6mMY1Kt+uGeOtcNuB3jXWlQ5Q4IL1c2aMj2SEWpIllGfuotPEppFfoFkCTjyHsOTjd6j8EZAOPCYAdskMRWo0+LODBaGLJ3YNKFOnhgrRRtbfZwJjb7NHbhAFLEFvp79+bSIOQLmO/2Jxgha9PgZBBjxoa7GTNl8otAKPI08ZtL3dHVYmopSQG+T58XDuWBATTZjWKbpIN0BI6Rd8v69TsY5Ctxuf8cLtUfJKJAQp81G7/5sz2vr2uCj1Sgr07LvKQek2bCWhn/BqtxmXSYyfFgmhR/asbixckK5edRVBWWDKUmaESuB08eCFpf1OO/BMtWLLMQ6gjpguVqYk9YA1sgjvkc5z7O5qJhAgiBIAkXnUGmecZXz0/TtaQKR4zFDGvObtKmYfaJMNg0W3/pbzzuZ7UtF7O2iirKBn4dj/6t9+WsO76qXyZKWw6V6aLJHklS++9TFqf4U9dsItattmA8IKUH5etDQA+KGD0ta2vslE9lYelbvpUqzFsfE3JRA1hPTEhdgNE8InOaGaIsTwmXSGPDWaFZAcYqL9+2reekflU4MMy/P8gpS1h/rd56PD+zax51SC8cZjbg7bi1v+SzDCTFU/ZXgzMNk6wCD3NTtQ1eSyhDAiRnM4GBJNGJe2GHknGBygboWN mkjZHH4y eB0UuoLObgldrP2Bno9gnz04Zp804LiwIN0pzwJZ3SiuvpERSdIpDdjrDp+2JmjmARMcQ6WvHleGnLhTefQ6d14G+Tzt29NP7k4cv/iPeHNflPtaxjNSHKPo6Gc6YXh8dRCfmeKh080z64jYIXO+RrAjAlsiZfl866Vd//WZaA44oCjVQj4CZRv/kOKjrR2dCTghYYFZTbroMSFwKb6UrLXCjJoWSY4GzssVd6ulsK64OFqmDQ00T80M0/yOudl73s3FGuNRpSFyJkXJbiZSEax1yRqhvTB85FiO7p0lprQ5XwduHd4EgCSMNe9nidEIBXMuzbV56iPnv7TweYQUsw0MS8+XTl9vaoUNc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 18, 2026 at 08:06:34PM +0000, David Matlack wrote: > Save the ACS Control register in pci_save_state() and write it back > in pci_restore_state(), instead of recomputing the ACS controls from > scratch with pci_enable_acs(). > > This makes ACS symmetric with the rest of a device's saved state. Today > pci_save_state() ignores ACS entirely and pci_restore_state() re-enables > the ACS controls from the kernel's current ACS policy. As a result, a > device can come out of a reset with different ACS controls than it went > in with, e.g. any controls programmed outside of pci_enable_acs() are > silently dropped. > > pci_enable_acs() runs when a driver binds to a device > (pci_dma_configure()), i.e. after pci_bus_add_device() has already saved > the device's state. Refresh the saved ACS Control register there as > well, otherwise a subsequent reset would revert ACS back to the > configuration left behind by firmware. > > Devices that rely on device-specific quirks to enable an ACS equivalent > keep that configuration outside of the ACS Control register, so keep > configuring ACS from scratch for them. Do the same for devices that have > no saved ACS state at all. > > Reviewed-by: Bjorn Helgaas > Assisted-by: Claude:claude-opus-5 > Signed-off-by: David Matlack Reviewed-by: Pranjal Shrivastava Thanks, Praan