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[91.79.175.49]) by smtp.googlemail.com with ESMTPSA id u11sm2214991lfb.85.2019.01.26.13.24.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 26 Jan 2019 13:24:37 -0800 (PST) Subject: Re: [PATCH V3 3/3] i2c: tegra: Add DMA Support To: Sowjanya Komatineni , thierry.reding@gmail.com, jonathanh@nvidia.com, mkarthik@nvidia.com, smohammed@nvidia.com, talho@nvidia.com Cc: linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org References: <1548475073-12408-1-git-send-email-skomatineni@nvidia.com> <1548475073-12408-3-git-send-email-skomatineni@nvidia.com> From: Dmitry Osipenko Message-ID: <5973707c-555f-a27c-2ff3-e867d4b2cde7@gmail.com> Date: Sun, 27 Jan 2019 00:24:36 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <1548475073-12408-3-git-send-email-skomatineni@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 26.01.2019 6:57, Sowjanya Komatineni пишет: > This patch adds DMA support for Tegra I2C. > > Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for > transfer size of the max FIFO depth and DMA mode is used for > transfer size higher than max FIFO depth to save CPU overhead. > > PIO mode needs full intervention of CPU to fill or empty FIFO's > and also need to service multiple data requests interrupt for the > same transaction adding overhead on CPU for large transfers. > > DMA mode is helpful for Large transfers during downloading or > uploading FW over I2C to some external devices. > > Signed-off-by: Sowjanya Komatineni > > --- Seems there are good news, APB DMA could access IRAM. Quote from TRM: "The source may be DRAM or IRAM, and the destination location could be devices placed on APB Bus; or vice versa". Hence it shall be much more efficient to use IRAM for the DMA buffer, please consider that variant.