From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shuah Khan Subject: Re: [PATCH 4/4] i2c: rcar: check for DMA-capable buffers Date: Thu, 15 Jun 2017 13:48:17 -0600 Message-ID: References: <20170615183039.22925-1-wsa+renesas@sang-engineering.com> <20170615183039.22925-5-wsa+renesas@sang-engineering.com> <20170615191743.xdrvigy4h2gqk2kk@ninjato> Reply-To: shuah@kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20170615191743.xdrvigy4h2gqk2kk@ninjato> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Wolfram Sang , Shuah Khan Cc: Wolfram Sang , linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org, LKML , Shuah Khan List-Id: linux-i2c@vger.kernel.org On 06/15/2017 01:17 PM, Wolfram Sang wrote: > Hi, > >>> - /* Do not use DMA if it's not available or for messages < 8 bytes */ >>> - if (IS_ERR(chan) || msg->len < 8) >>> + if (IS_ERR(chan) || msg->len < RCAR_DMA_THRESHOLD || priv->flags & ID_P_NODMA) >> >> Might be more efficient to check for ID_P_NODMA first instead of msg->len. > > I think most of the I2C transfers are smaller (like reading/writing one > register) than the threshold, so this "should" be more efficient. Plus, > honestly, I also think this is a micro-optimization which is largely > depending on the use-case. Can we agree on that? Makes sense. > >>> - read = msg->flags & I2C_M_RD; >>> + /* we need to check here because we need the 'current' context */ >>> + if (i2c_check_msg_for_dma(msg, RCAR_DMA_THRESHOLD, NULL) == -EFAULT) { >>> + dev_dbg(dev, "skipping DMA for this whole transfer\n"); >> >> Adding reason for skipping will be helpful. > > The I2C core helper will immediately print before that the buffer is not > DMA capable. Do you think this together will do? That is sufficient. thanks, -- Shuah > > Thanks for your input, > > Wolfram >