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Tue, 2 Jul 2024 06:03:58 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.11.0-alpha0-566-g3812ddbbc-fm-20240627.001-g3812ddbb Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: In-Reply-To: References: <20240629052247.2653363-1-uwu@icenowy.me> <20240629052247.2653363-3-uwu@icenowy.me> <2760BA02-8FF8-4B29-BFE2-1322B5BFB6EC@icenowy.me> <7e30177b-ff13-4fed-aa51-47a9cbd5d572@amd.com> <6303afecce2dff9e7d30f67e0a74205256e0a524.camel@icenowy.me> Date: Tue, 02 Jul 2024 18:03:37 +0800 From: "Jiaxun Yang" To: =?UTF-8?Q?Christian_K=C3=B6nig?= , "Icenowy Zheng" , "Huang Rui" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "David Airlie" , "Daniel Vetter" Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/2] drm/ttm: downgrade cached to write_combined when snooping not available Content-Type: text/plain;charset=utf-8 Content-Transfer-Encoding: quoted-printable =E5=9C=A82024=E5=B9=B47=E6=9C=882=E6=97=A5=E4=B8=83=E6=9C=88 =E4=B8=8B=E5= =8D=885:27=EF=BC=8CChristian K=C3=B6nig=E5=86=99=E9=81=93=EF=BC=9A > Am 02.07.24 um 11:06 schrieb Icenowy Zheng: >> [SNIP] However I don't think the definition of the AGP spec could app= ly on all >> PCI(e) implementations. The AGP spec itself don't apply on >> implementations that do not implement AGP (which is the most PCI(e) >> implementations today), and it's not in the reference list of the PCIe >> spec, so it does no help on this context.=20 > No, exactly that is not correct. > > See as I explained the No-Snoop extension to PCIe was created to help=20 > with AGP support and later merged into the base PCIe specification. > > So the AGP spec is now part of the PCIe spec. We don't really buy this theory. Keyword "AGP" doesn't appear in "PCI Express Base 4.0 Base Specification= " even once. If PCIe is a predecessor of AGP, where does AGP specific software interf= ace like AGP aperture goes? PCIe GPUs are only borrowing software concepts from = AGP, but they didn't inherit any hardware properties. [...] > We seem to have a misunderstanding here, this is not a software issue.=20 > The hardware platform is considered broken by the hardware vendor! It's up to the specification text to define compliance means. So far as = per analysis from Icenowy of PCIe specification text itself it's not prohibited. > > In other words people have stitched together hardware in a way which i= s=20 > not supported by the creator of that hardware. > > So as long as you can't convince anybody from ARM or the RISC-V team o= r=20 > whoever created that hardware to confirm that the hardware actually=20 > works you won't get any support for that. Well we are trying to support them on our own in mainline, we are not as= king for any support. Thanks - Jiaxun > > Regards, > Christian. --=20 - Jiaxun