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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a54b7asm2782895f8f.16.2025.06.13.08.56.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Jun 2025 08:56:40 -0700 (PDT) Date: Fri, 13 Jun 2025 16:56:38 +0100 From: David Laight To: James Clark Cc: Frank Li , Vladimir Oltean , Mark Brown , Vladimir Oltean , linux-spi@vger.kernel.org, imx@lists.linux.dev, linux-kernel@vger.kernel.org, Arnd Bergmann Subject: Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA Message-ID: <20250613165638.5d8ed000@pumpkin> In-Reply-To: References: <20250609-james-nxp-spi-dma-v1-0-2b831e714be2@linaro.org> <20250609-james-nxp-spi-dma-v1-2-2b831e714be2@linaro.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 10 Jun 2025 16:46:36 +0100 James Clark wrote: > On 10/06/2025 4:15 pm, Frank Li wrote: > > On Mon, Jun 09, 2025 at 04:32:39PM +0100, James Clark wrote: > >> Using coherent memory here isn't functionally necessary. > >> Because the > >> change to use non-coherent memory isn't overly complex and only a few > >> synchronization points are required, we might as well do it while fixing > >> up some other DMA issues. > > > > Any beanfit by use on-coherent memory here? > > > > Frank > > > > Presumably less cache maintenance traffic? I bet it only helps when cache-coherent memory has to be uncached. Otherwise the software cache operations are pretty much guaranteed to be more expensive than the hardware ones. David