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Hermes SMTP Server) with ESMTPA ID e1d66fb77c6e6fa7c9b4de4032fbb07e; Mon, 15 Dec 2025 20:50:04 +0000 (UTC) From: Andrei-Edward Popa To: robin.murphy@arm.com, m.szyprowski@samsung.com, hch@infradead.org Cc: andrei.popa105@yahoo.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dma-remap: fix dma_common_find_pages() page lookup for offsets Date: Mon, 15 Dec 2025 22:49:55 +0200 Message-ID: <20251215204956.20659-1-andrei.popa105@yahoo.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: 1d552f40-74b3-4c6d-874d-508ecb0e75d2@arm.com References: <1d552f40-74b3-4c6d-874d-508ecb0e75d2@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Christoph, Marek, Robin, Thanks for the detailed explanations, that clarified things a lot. I now understand that dma_mmap_attrs() expects cpu_addr to be the exact pointer returned by dma_alloc_attrs(), and that subdividing an allocation (e.g. via gen_pool) requires the driver to keep track of offsets and adjust the mmap parameters accordingly before calling into the DMA API. My patch was effectively trying to make dma_common_find_pages() accept offset cpu_addr values implicitly, which would change the DMA API semantics and mask driver bugs rather than fixing them in the driver itself. Given this, I agree that the correct fix is in the driver using the API, not in dma-remap, and I’ll drop this patch. Thanks again for taking the time to explain the intended usage and constraints of the DMA mmap helpers. Best regards, Andrei