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[173.246.12.168]) by smtp.gmail.com with ESMTPSA id i5sm13131110qkg.32.2021.02.15.12.39.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Feb 2021 12:39:27 -0800 (PST) Message-ID: Subject: Re: DMA-buf and uncached system memory From: Nicolas Dufresne To: Christian =?ISO-8859-1?Q?K=F6nig?= , linux-media , dri-devel , linaro-mm-sig@lists.linaro.org, lkml Cc: Sumit Semwal , Daniel Vetter , "Sharma, Shashank" Date: Mon, 15 Feb 2021 15:39:25 -0500 In-Reply-To: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> References: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.3 (3.38.3-1.fc33) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le lundi 15 février 2021 à 09:58 +0100, Christian König a écrit : > Hi guys, > > we are currently working an Freesync and direct scan out from system > memory on AMD APUs in A+A laptops. > > On problem we stumbled over is that our display hardware needs to scan > out from uncached system memory and we currently don't have a way to > communicate that through DMA-buf. > > For our specific use case at hand we are going to implement something > driver specific, but the question is should we have something more > generic for this? Hopefully I'm getting this right, but this makes me think of a long standing issue I've met with Intel DRM and UVC driver. If I let the UVC driver allocate the buffer, and import the resulting DMABuf (cacheable memory written with a cpu copy in the kernel) into DRM, we can see cache artifact being displayed. While if I use the DRM driver memory (dumb buffer in that case) it's clean because there is a driver specific solution to that. There is no obvious way for userspace application to know what's is right/wrong way and in fact it feels like the kernel could solve this somehow without having to inform userspace (perhaps). > > After all the system memory access pattern is a PCIe extension and as > such something generic. > > Regards, > Christian. 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[173.246.12.168]) by smtp.gmail.com with ESMTPSA id i5sm13131110qkg.32.2021.02.15.12.39.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Feb 2021 12:39:27 -0800 (PST) Message-ID: Subject: Re: DMA-buf and uncached system memory From: Nicolas Dufresne To: Christian =?ISO-8859-1?Q?K=F6nig?= , linux-media , dri-devel , linaro-mm-sig@lists.linaro.org, lkml Date: Mon, 15 Feb 2021 15:39:25 -0500 In-Reply-To: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> References: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> User-Agent: Evolution 3.38.3 (3.38.3-1.fc33) MIME-Version: 1.0 X-Mailman-Approved-At: Mon, 15 Feb 2021 22:24:30 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Sharma, Shashank" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" TGUgbHVuZGkgMTUgZsOpdnJpZXIgMjAyMSDDoCAwOTo1OCArMDEwMCwgQ2hyaXN0aWFuIEvDtm5p ZyBhIMOpY3JpdMKgOgo+IEhpIGd1eXMsCj4gCj4gd2UgYXJlIGN1cnJlbnRseSB3b3JraW5nIGFu IEZyZWVzeW5jIGFuZCBkaXJlY3Qgc2NhbiBvdXQgZnJvbSBzeXN0ZW0gCj4gbWVtb3J5IG9uIEFN RCBBUFVzIGluIEErQSBsYXB0b3BzLgo+IAo+IE9uIHByb2JsZW0gd2Ugc3R1bWJsZWQgb3ZlciBp cyB0aGF0IG91ciBkaXNwbGF5IGhhcmR3YXJlIG5lZWRzIHRvIHNjYW4gCj4gb3V0IGZyb20gdW5j YWNoZWQgc3lzdGVtIG1lbW9yeSBhbmQgd2UgY3VycmVudGx5IGRvbid0IGhhdmUgYSB3YXkgdG8g Cj4gY29tbXVuaWNhdGUgdGhhdCB0aHJvdWdoIERNQS1idWYuCj4gCj4gRm9yIG91ciBzcGVjaWZp YyB1c2UgY2FzZSBhdCBoYW5kIHdlIGFyZSBnb2luZyB0byBpbXBsZW1lbnQgc29tZXRoaW5nIAo+ IGRyaXZlciBzcGVjaWZpYywgYnV0IHRoZSBxdWVzdGlvbiBpcyBzaG91bGQgd2UgaGF2ZSBzb21l dGhpbmcgbW9yZSAKPiBnZW5lcmljIGZvciB0aGlzPwoKSG9wZWZ1bGx5IEknbSBnZXR0aW5nIHRo aXMgcmlnaHQsIGJ1dCB0aGlzIG1ha2VzIG1lIHRoaW5rIG9mIGEgbG9uZyBzdGFuZGluZwppc3N1 ZSBJJ3ZlIG1ldCB3aXRoIEludGVsIERSTSBhbmQgVVZDIGRyaXZlci4gSWYgSSBsZXQgdGhlIFVW QyBkcml2ZXIgYWxsb2NhdGUKdGhlIGJ1ZmZlciwgYW5kIGltcG9ydCB0aGUgcmVzdWx0aW5nIERN QUJ1ZiAoY2FjaGVhYmxlIG1lbW9yeSB3cml0dGVuIHdpdGggYSBjcHUKY29weSBpbiB0aGUga2Vy bmVsKSBpbnRvIERSTSwgd2UgY2FuIHNlZSBjYWNoZSBhcnRpZmFjdCBiZWluZyBkaXNwbGF5ZWQu IFdoaWxlCmlmIEkgdXNlIHRoZSBEUk0gZHJpdmVyIG1lbW9yeSAoZHVtYiBidWZmZXIgaW4gdGhh dCBjYXNlKSBpdCdzIGNsZWFuIGJlY2F1c2UKdGhlcmUgaXMgYSBkcml2ZXIgc3BlY2lmaWMgc29s dXRpb24gdG8gdGhhdC4KClRoZXJlIGlzIG5vIG9idmlvdXMgd2F5IGZvciB1c2Vyc3BhY2UgYXBw bGljYXRpb24gdG8ga25vdyB3aGF0J3MgaXMgcmlnaHQvd3JvbmcKd2F5IGFuZCBpbiBmYWN0IGl0 IGZlZWxzIGxpa2UgdGhlIGtlcm5lbCBjb3VsZCBzb2x2ZSB0aGlzIHNvbWVob3cgd2l0aG91dCBo YXZpbmcKdG8gaW5mb3JtIHVzZXJzcGFjZSAocGVyaGFwcykuCgo+IAo+IEFmdGVyIGFsbCB0aGUg c3lzdGVtIG1lbW9yeSBhY2Nlc3MgcGF0dGVybiBpcyBhIFBDSWUgZXh0ZW5zaW9uIGFuZCBhcyAK PiBzdWNoIHNvbWV0aGluZyBnZW5lcmljLgo+IAo+IFJlZ2FyZHMsCj4gQ2hyaXN0aWFuLgoKCl9f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmRyaS1kZXZlbCBt YWlsaW5nIGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpodHRwczovL2xpc3Rz LmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1kZXZlbAo=