linux-kernel - Re: [PATCH v2] mtd: rawnand: Fix return value check of wait_for_completion

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Message-ID: <20220412090649.33bb3f8b@xps13>
Date:   Tue, 12 Apr 2022 09:06:49 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Miaoqian Lin <linmq006@...il.com>
Cc:     Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Pratyush Yadav <p.yadav@...com>,
        Paul Cercueil <paul@...pouillou.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Bastian Hecht <hechtb@...glemail.com>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Guennadi Liakhovetski <g.liakhovetski@....de>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mtd: rawnand: Fix return value check of
 wait_for_completion_timeout

Hi Miaoqian,

linmq006@...il.com wrote on Tue, 12 Apr 2022 06:36:52 +0000:

> wait_for_completion_timeout() returns unsigned long not int.
> It returns 0 if timed out, and positive if completed.
> The check for <= 0 is ambiguous and should be == 0 here
> indicating timeout which is the only error case.
> 
> Fixes: 83738d87e3a0 ("mtd: sh_flctl: Add DMA capabilty")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
> change in v2:
> - initialize ret to 1.
> ---
>  drivers/mtd/nand/raw/sh_flctl.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/sh_flctl.c b/drivers/mtd/nand/raw/sh_flctl.c
> index b85b9c6fcc42..2373251f585b 100644
> --- a/drivers/mtd/nand/raw/sh_flctl.c
> +++ b/drivers/mtd/nand/raw/sh_flctl.c
> @@ -384,7 +384,8 @@ static int flctl_dma_fifo0_transfer(struct sh_flctl *flctl, unsigned long *buf,
>  	dma_addr_t dma_addr;
>  	dma_cookie_t cookie;
>  	uint32_t reg;
> -	int ret;
> +	int ret = 1;

Does not look right. I know this function returns > 0 on positive
outcomes but this does not make any sense in the first place.

This function is static and only called twice, please turn it into
something like:

if (dma_fifo_transfer())
	error
else
	ok

> +	unsigned long time_left;
>  
>  	if (dir == DMA_FROM_DEVICE) {
>  		chan = flctl->chan_fifo0_rx;
> @@ -425,13 +426,14 @@ static int flctl_dma_fifo0_transfer(struct sh_flctl *flctl, unsigned long *buf,
>  		goto out;
>  	}
>  
> -	ret =
> +	time_left =
>  	wait_for_completion_timeout(&flctl->dma_complete,
>  				msecs_to_jiffies(3000));
>  
> -	if (ret <= 0) {
> +	if (time_left == 0) {
>  		dmaengine_terminate_all(chan);
>  		dev_err(&flctl->pdev->dev, "wait_for_completion_timeout\n");
> +		ret = -ETIMEDOUT;
>  	}
>  
>  out:


Thanks,
Miquèl