linux-kernel - Re: [PATCH v2] i2c: mediatek: fix potential incorrect use of I2C_MASTER

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Message-ID: <zddsit53dwqo27buoxaolgpzvvvd6uvwcyzughv7qfvwg64ces@yrlrur5dkf45>
Date: Tue, 9 Sep 2025 00:17:14 +0200
From: Andi Shyti <andi.shyti@...nel.org>
To: Leilk Liu <leilk.liu@...iatek.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Qii Wang <qii.wang@...iatek.com>, Wolfram Sang <wsa@...nel.org>, 
	Liguo Zhang <liguo.zhang@...iatek.com>, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	Project_Global_Chrome_Upstream_Group@...iatek.com, Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [PATCH v2] i2c: mediatek: fix potential incorrect use of
 I2C_MASTER_WRRD

Hi Leilk,

> diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
> index ab456c3717db..dee40704825c 100644
> --- a/drivers/i2c/busses/i2c-mt65xx.c
> +++ b/drivers/i2c/busses/i2c-mt65xx.c
> @@ -1243,6 +1243,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
>  {
>  	int ret;
>  	int left_num = num;
> +	bool write_then_read_en = false;
>  	struct mtk_i2c *i2c = i2c_get_adapdata(adap);
>  
>  	ret = clk_bulk_enable(I2C_MT65XX_CLK_MAX, i2c->clocks);
> @@ -1256,6 +1257,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
>  		if (!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
>  		    msgs[0].addr == msgs[1].addr) {
>  			i2c->auto_restart = 0;
> +			write_then_read_en = true;
>  		}
>  	}
>  
> @@ -1280,12 +1282,10 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
>  		else
>  			i2c->op = I2C_MASTER_WR;
>  
> -		if (!i2c->auto_restart) {
> -			if (num > 1) {
> -				/* combined two messages into one transaction */
> -				i2c->op = I2C_MASTER_WRRD;
> -				left_num--;
> -			}
> +		if (write_then_read_en) {
> +			/* combined two messages into one transaction */
> +			i2c->op = I2C_MASTER_WRRD;

i2c doesn't change for the whole loop so that it can be set only
once outside the loop instead of setting it everytime.

Something like this:

	if (i2c->op == I2C_MASTER_WRRD)
		left_num--;
	else if (msgs->flags & I2C_M_RD)
		...
	else

looks cleaner to me and we save the extra flag. Am I missing
anything?

Andi

> +			left_num--;
>  		}
>  
>  		/* always use DMA mode. */
> @@ -1293,7 +1293,10 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
>  		if (ret < 0)
>  			goto err_exit;
>  
> -		msgs++;
> +		if (i2c->op == I2C_MASTER_WRRD)
> +			msgs += 2;
> +		else
> +			msgs++;
>  	}
>  	/* the return value is number of executed messages */
>  	ret = num;
> -- 
> 2.46.0
>