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[91.76.12.16]) by smtp.googlemail.com with ESMTPSA id 202sm2840464lfg.24.2020.07.23.06.17.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jul 2020 06:17:41 -0700 (PDT) Subject: Re: [PATCH 3/7] i2c: tegra: add flag for register write buffering To: Krishna Yarlagadda , linux-i2c@vger.kernel.org, thierry.reding@gmail.com Cc: jonathanh@nvidia.com, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, ldewangan@nvidia.com, smohammed@nvidia.com, rgumasta@nvidia.com References: <1595506733-10307-1-git-send-email-kyarlagadda@nvidia.com> <1595506733-10307-3-git-send-email-kyarlagadda@nvidia.com> From: Dmitry Osipenko Message-ID: Date: Thu, 23 Jul 2020 16:17:40 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <1595506733-10307-3-git-send-email-kyarlagadda@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 23.07.2020 15:18, Krishna Yarlagadda пишет: > In chips earlier to Tegra186, register write gets buffered. So to make > sure register writes are completed, there is need to readback the > register. Adding flag to disable this readback for Tegra186 and later > chips. > > Signed-off-by: Krishna Yarlagadda > --- > drivers/i2c/busses/i2c-tegra.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c > index a841d6c..bdbbca0 100644 > --- a/drivers/i2c/busses/i2c-tegra.c > +++ b/drivers/i2c/busses/i2c-tegra.c > @@ -220,6 +220,7 @@ struct tegra_i2c_hw_feature { > bool has_mst_fifo; > const struct i2c_adapter_quirks *quirks; > bool supports_bus_clear; > + bool has_reg_write_buffering; > bool has_apb_dma; > u8 tlow_std_mode; > u8 thigh_std_mode; > @@ -325,8 +326,11 @@ static void i2c_writel(struct tegra_i2c_dev *i2c_dev, u32 val, > writel_relaxed(val, i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg)); > > /* Read back register to make sure that register writes completed */ > - if (reg != I2C_TX_FIFO) > - readl_relaxed(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg)); > + if (i2c_dev->hw->has_reg_write_buffering) { > + if (reg != I2C_TX_FIFO) Should be single line. What problem does this solve? If there is no visible effect, then please drop this patch. > + readl_relaxed(i2c_dev->base + > + tegra_i2c_reg_addr(i2c_dev, reg)); > + }