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

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Message-ID: <61783400-4df2-47af-78a7-7acb715c3a71@gmail.com>
Date:   Tue, 12 Apr 2022 15:42:02 +0800
From:   Miaoqian Lin <linmq006@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.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 Miquel,

Thanks for your reply.

On 2022/4/12 15:06, Miquel Raynal wrote:
> 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.

Yes, I made a mistake, Now I realize that in v2, it will return 1 in error path

when DMA submit failed.

And for patch v1, it will return 0  if calls wait_for_completion_timeout succeeds.

> This function is static and only called twice, please turn it into
> something like:
>
> if (dma_fifo_transfer())
> 	error
> else
> 	ok

So I want to keep ret>0 means success.

Or could I set ret > 0 after in wait_for_completion_timeout() success path?

like:

    if(time_left == 0)

            ret = -ETIMEDOUT;

    else

            ret = 1;

What do you think?


Thanks,

>> +	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