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Tue, 22 Apr 2025 08:26:12 -0700 (PDT) Received: from [192.168.5.101] ([2602:f919:106::1b8]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22c50bf16b1sm86663765ad.89.2025.04.22.08.26.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Apr 2025 08:26:12 -0700 (PDT) Message-ID: <918e0177-8e26-405c-93ad-8b0d2dfd3b3d@gmail.com> Date: Tue, 22 Apr 2025 23:26:04 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: troymitchell988@gmail.com, Oleksij Rempel , Pengutronix Kernel Team , Andi Shyti , Shawn Guo , Sascha Hauer , Fabio Estevam , linux-i2c@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Yongchao Jia Subject: Re: [PATCH 1/2] i2c: imx: use guard to take spinlock To: Jonathan Cameron References: <20250421-i2c-imx-update-v1-0-1137f1f353d5@gmail.com> <20250421-i2c-imx-update-v1-1-1137f1f353d5@gmail.com> <20250422161213.0000597d@huawei.com> Content-Language: en-US From: Troy Mitchell In-Reply-To: <20250422161213.0000597d@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250422_082613_965529_9B6D192B X-CRM114-Status: GOOD ( 20.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2025/4/22 23:12, Jonathan Cameron wrote: > On Mon, 21 Apr 2025 13:36:38 +0800 > Troy Mitchell wrote: > >> Use guard to automatically release the lock after going out of scope >> instead of calling it manually. > Drive by review, but this changes behavior in a subtle way so we > should have more commentary here... Thanks for your review! > >> Co-developed-by: Yongchao Jia >> Signed-off-by: Yongchao Jia >> Signed-off-by: Troy Mitchell >> --- >> drivers/i2c/busses/i2c-imx.c | 22 ++++++++++------------ >> 1 file changed, 10 insertions(+), 12 deletions(-) >> >> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c >> index 9e5d454d8318..cb96a57df4a0 100644 >> --- a/drivers/i2c/busses/i2c-imx.c >> +++ b/drivers/i2c/busses/i2c-imx.c >> @@ -23,6 +23,7 @@ >> >> #include >> #include >> +#include >> #include >> #include >> #include >> >> @@ -1125,30 +1126,27 @@ static irqreturn_t i2c_imx_isr(int irq, void *dev_id) >> { >> struct imx_i2c_struct *i2c_imx = dev_id; >> unsigned int ctl, status; >> - unsigned long flags; >> >> - spin_lock_irqsave(&i2c_imx->slave_lock, flags); >> + guard(spinlock_irqsave)(&i2c_imx->slave_lock); >> + >> status = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR); >> ctl = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR); >> >> if (status & I2SR_IIF) { >> i2c_imx_clear_irq(i2c_imx, I2SR_IIF); >> + >> if (i2c_imx->slave) { >> if (!(ctl & I2CR_MSTA)) { >> irqreturn_t ret; >> >> - ret = i2c_imx_slave_handle(i2c_imx, >> - status, ctl); >> - spin_unlock_irqrestore(&i2c_imx->slave_lock, >> - flags); >> - return ret; >> + return i2c_imx_slave_handle(i2c_imx, >> + status, ctl); >> } >> i2c_imx_slave_finish_op(i2c_imx); >> } >> - spin_unlock_irqrestore(&i2c_imx->slave_lock, flags); > In this path the patch changes the lock release to occur after > i2c_imx_master_isr(i2c_imx, status); > > That may well be safe; I have no idea! You should talk about that > in the patch description if it is. You're correct that this change slightly alters the lock release timing. However, both i2c_imx_slave_handle() and i2c_imx_master_isr() can safely be entered with the lock held — there's no requirement for the lock to be released before calling them. Using guard(spinlock_irqsave) simplifies the control flow by ensuring consistent and automatic unlock, which improves readability without affecting correctness. I'll update the commit message to clarify this. > >> + >> return i2c_imx_master_isr(i2c_imx, status); >> } >> - spin_unlock_irqrestore(&i2c_imx->slave_lock, flags); >> >> return IRQ_NONE; >> } -- Troy Mitchell