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[109.252.170.211]) by smtp.googlemail.com with ESMTPSA id u2sm2913787ljo.48.2020.09.05.16.35.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Sep 2020 16:35:02 -0700 (PDT) Subject: Re: [PATCH v4 15/31] i2c: tegra: Remove bogus barrier() From: Dmitry Osipenko To: Thierry Reding , Jonathan Hunter , Laxman Dewangan , Wolfram Sang , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Andy Shevchenko Cc: linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200905204151.25343-1-digetx@gmail.com> <20200905204151.25343-16-digetx@gmail.com> Message-ID: Date: Sun, 6 Sep 2020 02:35:02 +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: <20200905204151.25343-16-digetx@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 05.09.2020 23:41, Dmitry Osipenko пишет: > Apparently barrier() was intended to reduce possibility of racing > with the interrupt handler, but driver's code evolved significantly > and today's driver enables interrupt only when it waits for completion > notification. Hence barrier() has no good use anymore, let's remove it. > > Signed-off-by: Dmitry Osipenko > --- > drivers/i2c/busses/i2c-tegra.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c > index 33d37a40fa83..f69587ca163b 100644 > --- a/drivers/i2c/busses/i2c-tegra.c > +++ b/drivers/i2c/busses/i2c-tegra.c > @@ -600,7 +600,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) > i2c_dev->msg_buf_remaining = buf_remaining; > i2c_dev->msg_buf = buf + > words_to_transfer * BYTES_PER_FIFO_WORD; > - barrier(); > > i2c_writesl(i2c_dev, buf, I2C_TX_FIFO, words_to_transfer); > > @@ -624,7 +623,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) > /* Again update before writing to FIFO to make sure isr sees. */ > i2c_dev->msg_buf_remaining = 0; > i2c_dev->msg_buf = NULL; > - barrier(); > > i2c_writel(i2c_dev, val, I2C_TX_FIFO); > } > It just caught my eye that there is actually a comment there saying that barrier() was intended to mitigate the racing with the ISR. Hence that comment is outdated now and needs to be removed. I'll correct it in v5.