From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1495803280.26190.37.camel@infradead.org> Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs From: David Woodhouse To: "Deucher, Alexander" , 'Joerg Roedel' Cc: 'Joerg Roedel' , Bjorn Helgaas , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Daniel Drake , Samuel Sieb In-Reply-To: References: <1491575538-22694-1-git-send-email-joro@8bytes.org> <1493893297.4904.71.camel@infradead.org> <20170524084450.GB12353@suse.de> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-TNY7NLHbjFGRLlYAZNMe" Date: Fri, 26 May 2017 13:54:40 +0100 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: --=-TNY7NLHbjFGRLlYAZNMe Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2017-05-26 at 11:57 +0000, Deucher, Alexander wrote: >=20 > FWIW, the GPU driver does not actually use ATS at the moment so I > don't think we should see any ATS transactions. That's a confusing sentence. The "GPU driver", if you mean software running in the OS, wouldn't be expected to have anything to do with ATS. ATS is something that the CPU itself (or its DMA engine) would do. Instead of just performing a DMA transaction to a given bus address, and letting the IOMMU do the translation, the hardware might choose to first perform an IOTLB lookup, and then later do the actual DMA transaction to the pre-translated, raw physical address. Which kind of makes a mockery of any kind of protection the IOMMU is supposed to give you, but does shave a cycle or two of latency off the DMA when it finally happens, since the translation can be done in advance. --=-TNY7NLHbjFGRLlYAZNMe Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDzUw ggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQswCQYDVQQG EwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVybmFsIFRU UCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MB4XDTE0MTIyMjAw MDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1h bmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMUEw PwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBF 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