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

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Message-ID: <20220412094822.3818ebc2@xps13>
Date:   Tue, 12 Apr 2022 09:48:22 +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 15:42:02 +0800:

> 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.

Not 1, but a proper error code please (-ETIMEDOUT, -EINVAL, whatever)

> 
> 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;

You can initialize ret to zero at to top. So that anything != 0 is an
error (like a lot of functions in the kernel). And use:

	if (dma_fifo_transfer())
		error();

> 
> 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  


Thanks,
Miquèl