linux-kernel - Re: [PATCH v2 1/3] i2c: imx-lpi2c: directly return ISR when detect a NACK

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Message-ID: <20230725235511.lt62ubfw7geu5cfu@intel.intel>
Date:   Wed, 26 Jul 2023 01:55:11 +0200
From:   Andi Shyti <andi.shyti@...nel.org>
To:     carlos.song@....com
Cc:     aisheng.dong@....com, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, xiaoning.wang@....com,
        haibo.chen@....com, linux-imx@....com, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] i2c: imx-lpi2c: directly return ISR when detect a
 NACK

Hi Carlos,

On Mon, Jul 24, 2023 at 06:55:44PM +0800, carlos.song@....com wrote:
> From: Gao Pan <pandy.gao@....com>
> 
> A NACK flag in ISR means i2c bus error. In such codition,
> there is no need to do read/write operation. It's better
> to return ISR directly and then stop i2c transfer.
> 
> Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> Signed-off-by: Gao Pan <pandy.gao@....com>
> Signed-off-by: Carlos Song <carlos.song@....com>
> ---
>  drivers/i2c/busses/i2c-imx-lpi2c.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
> index c3287c887c6f..158de0b7f030 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -514,15 +514,14 @@ static irqreturn_t lpi2c_imx_isr(int irq, void *dev_id)
>  	temp = readl(lpi2c_imx->base + LPI2C_MSR);
>  	temp &= enabled;
>  
> -	if (temp & MSR_RDF)
> +	if (temp & MSR_NDF) {
> +		complete(&lpi2c_imx->complete);
> +		return IRQ_HANDLED;

you can actually remove the return here

	if (temp & MSR_NDF)
		complete();
	else if (temp & MSR_RDF)
		exfifo();
	else if (temp & MSR_TDF)
		txfifo();

	return IRQ_HANDLED;


BTW, the logic here is changing, as well and it's not described
in the commit log. This patch is not only stopping when a nack is
received (MSR_NDF), but it's also making mutually exclusive
read/write (which I guess are MSR_RDF and MSR_TDF).

Is this what you want? If so, can you please describe it in the
commit log or add a comment describing that the three states are
all mutually exclusive.

Thanks,
Andi


> +	} else if (temp & MSR_RDF)
>  		lpi2c_imx_read_rxfifo(lpi2c_imx);
> -
> -	if (temp & MSR_TDF)
> +	else if (temp & MSR_TDF)
>  		lpi2c_imx_write_txfifo(lpi2c_imx);
>  
> -	if (temp & MSR_NDF)
> -		complete(&lpi2c_imx->complete);
> -
>  	return IRQ_HANDLED;
>  }
>  
> -- 
> 2.34.1
>