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[80.7.220.175]) by smtp.gmail.com with ESMTPSA id u12-20020adfdb8c000000b002119c1a03e4sm22758115wri.31.2022.06.09.02.19.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jun 2022 02:19:24 -0700 (PDT) Date: Thu, 9 Jun 2022 10:19:22 +0100 From: Daniel Thompson To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Lucas Stach Subject: Re: [RESEND PATCH v3] drm/cma-helper: Describe what a "contiguous chunk" actually means Message-ID: <20220609091922.6gn2nlysrpndfu4n@maple.lan> References: <20220608135821.1153346-1-daniel.thompson@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 08, 2022 at 05:37:50PM +0200, Daniel Vetter wrote: > On Wed, Jun 08, 2022 at 02:58:21PM +0100, Daniel Thompson wrote: > > Since it's inception in 2012 it has been understood that the DRM GEM CMA > > helpers do not depend on CMA as the backend allocator. In fact the first > > bug fix to ensure the cma-helpers work correctly with an IOMMU backend > > appeared in 2014. However currently the documentation for > > drm_gem_cma_create() talks about "a contiguous chunk of memory" without > > making clear which address space it will be a contiguous part of. > > Additionally the CMA introduction is actively misleading because it only > > contemplates the CMA backend. > > > > This matters because when the device accesses the bus through an IOMMU > > (and don't use the CMA backend) then the allocated memory is contiguous > > only in the IOVA space. This is a significant difference compared to the > > CMA backend and the behaviour can be a surprise even to someone who does > > a reasonable level of code browsing (but doesn't find all the relevant > > function pointers ;-) ). > > > > Improve the kernel doc comments accordingly. > > > > Signed-off-by: Daniel Thompson > > Reviewed-by: Lucas Stach > > --- > > > > Notes: > > Am I Cc:ing the correct reviewers/maintainers with this patch? There > > has been no negative feedback but I've been rebasing and re-posting it > > for three kernel cycles now. Do I need to queue it somewhere special or > > get it in front of someone specific? > > Occasionally stuff falls through a few too many cracks, that's all. We > have tons of committers for drm-misc (and Lucas is one of them), but > sometimes they shy away from pushing themselves and others see the r-b and > assume it's already handled, and then it doesn't move :-/ No worries. Arguably I should have asked this question a little earlier anyway. Thanks for pushing it. Daniel.