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[91.79.175.49]) by smtp.googlemail.com with ESMTPSA id u68sm24902312pfj.180.2019.02.02.06.13.58 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 02 Feb 2019 06:14:04 -0800 (PST) Subject: Re: [PATCH V9 3/5] i2c: tegra: Add DMA support From: Dmitry Osipenko To: Sowjanya Komatineni , "thierry.reding@gmail.com" , Jonathan Hunter , Mantravadi Karthik , Shardar Mohammed , Timo Alho Cc: "linux-tegra@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-i2c@vger.kernel.org" References: <1549040867-18149-1-git-send-email-skomatineni@nvidia.com> <1549040867-18149-3-git-send-email-skomatineni@nvidia.com> <951cf1f5-ba3a-94ef-0399-2259effebc99@gmail.com> <6150de70-6ca8-944a-780a-4574ff2b21c7@gmail.com> Message-ID: Date: Sat, 2 Feb 2019 17:13:56 +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: <6150de70-6ca8-944a-780a-4574ff2b21c7@gmail.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 01.02.2019 22:22, Dmitry Osipenko пишет: > 01.02.2019 22:20, Sowjanya Komatineni пишет: >> >>>> +static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev) { >>>> + struct dma_chan *dma_chan; >>>> + u32 *dma_buf; >>>> + dma_addr_t dma_phys; >>>> + int err = 0; >>>> + >>>> + if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA)) >>>> + return -ENODEV; >>> >>> Driver shall not fail to probe if DMA driver is disabled, but to continue with the PIO-only mode available. >>> >>> Should be: >>> >>> if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA)) >>> return 0; >>> >> Except EPROBE_DEFER, anything else returned from tegra_i2c_init_dma (ENODEV/ENOMEM) is ignored in i2c_probe >> DMA mode decision is based on xfer size and availability of dma channel or can be changed based on valid dma buf to shorten the line. >> > > Ah, sorry. I missed that, seems good then. > BTW, it may be worthwhile to move out the error code handling into tegra_i2c_init_dma() for clarity. It also won't hurt to not ignore errors other than -ENODEV. diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c index 32d5744bce45..684a0689ac8d 100644 --- a/drivers/i2c/busses/i2c-tegra.c +++ b/drivers/i2c/busses/i2c-tegra.c @@ -397,7 +397,7 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev) int err = 0; if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA)) - return -ENODEV; + return 0; dma_chan = dma_request_slave_channel_reason(i2c_dev->dev, "rx"); if (IS_ERR(dma_chan)) @@ -434,6 +434,13 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev) if (i2c_dev->rx_dma_chan) dma_release_channel(i2c_dev->rx_dma_chan); + /* + * -ENODEV is likely due to a missing "dmas" property, driver falls + * back to PIO in this case. + */ + if (err == -ENODEV) + return 0; + return err; } @@ -1553,7 +1560,7 @@ static int tegra_i2c_probe(struct platform_device *pdev) } ret = tegra_i2c_init_dma(i2c_dev); - if (ret == -EPROBE_DEFER) + if (ret) goto disable_div_clk; ret = tegra_i2c_init(i2c_dev, false);