linux-kernel - Re: [PATCH 1/2] i2c: imx: use guard to take spinlock

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Message-ID: <20250422161213.0000597d@huawei.com>
Date: Tue, 22 Apr 2025 16:12:13 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Troy Mitchell <troymitchell988@...il.com>
CC: Oleksij Rempel <o.rempel@...gutronix.de>, Pengutronix Kernel Team
	<kernel@...gutronix.de>, Andi Shyti <andi.shyti@...nel.org>, Shawn Guo
	<shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Fabio Estevam
	<festevam@...il.com>, <linux-i2c@...r.kernel.org>, <imx@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	Yongchao Jia <jyc0019@...il.com>
Subject: Re: [PATCH 1/2] i2c: imx: use guard to take spinlock

On Mon, 21 Apr 2025 13:36:38 +0800
Troy Mitchell <troymitchell988@...il.com> 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...

> 
> Co-developed-by: Yongchao Jia <jyc0019@...il.com>
> Signed-off-by: Yongchao Jia <jyc0019@...il.com>
> Signed-off-by: Troy Mitchell <troymitchell988@...il.com>
> ---
>  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 <linux/acpi.h>
>  #include <linux/clk.h>
> +#include <linux/cleanup.h>
>  #include <linux/completion.h>
>  #include <linux/delay.h>
>  #include <linux/dma-mapping.h>

>  
> @@ -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.

> +
>  		return i2c_imx_master_isr(i2c_imx, status);
>  	}
> -	spin_unlock_irqrestore(&i2c_imx->slave_lock, flags);
>  
>  	return IRQ_NONE;
>  }
>