linux-kernel - Re: [PATCH next] mtd: rawnand: loongson1: Fix error code in ls1x_nand_dma

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Message-ID: <CAJhJPsV8Pb7gXFX2gqFVYcp4O7N=zL5V+QGkfYn73UYK67zYfg@mail.gmail.com>
Date: Tue, 6 May 2025 20:12:11 +0800
From: Keguang Zhang <keguang.zhang@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Miquel Raynal <miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, 
	Vignesh Raghavendra <vigneshr@...com>, linux-mips@...r.kernel.org, linux-mtd@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] mtd: rawnand: loongson1: Fix error code in ls1x_nand_dma_transfer()

On Tue, May 6, 2025 at 7:16 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> On Tue, May 06, 2025 at 06:01:15PM +0800, Keguang Zhang wrote:
> > On Tue, May 6, 2025 at 5:32 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > >
> > > On Tue, May 06, 2025 at 05:16:03PM +0800, Keguang Zhang wrote:
> > > > On Fri, May 2, 2025 at 4:39 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > > > >
> > > > > The "desc" variable is NULL and PTR_ERR(NULL) is zero/success.  Return
> > > > > a negative error code instead.
> > > > >
> > > > > Fixes: d2d10ede04b1 ("mtd: rawnand: Add Loongson-1 NAND Controller Driver")
> > > > > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> > > > > ---
> > > > > It's hard to know what the patch prefix should be here.  Ideally when we
> > > > > add a new driver we would use the patch prefix for the driver.
> > > > >
> > > > > Tired: subsystem: Add driver XXX
> > > > > Wired: subsystem: XXX: Add driver for XXX
> > > > >
> > > > >  drivers/mtd/nand/raw/loongson1-nand-controller.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/mtd/nand/raw/loongson1-nand-controller.c b/drivers/mtd/nand/raw/loongson1-nand-controller.c
> > > > > index 6a369b1c7d86..8754bb4f8b56 100644
> > > > > --- a/drivers/mtd/nand/raw/loongson1-nand-controller.c
> > > > > +++ b/drivers/mtd/nand/raw/loongson1-nand-controller.c
> > > > > @@ -371,7 +371,7 @@ static int ls1x_nand_dma_transfer(struct ls1x_nand_host *host, struct ls1x_nand_
> > > > >         desc = dmaengine_prep_slave_single(chan, dma_addr, op->len, xfer_dir, DMA_PREP_INTERRUPT);
> > > > >         if (!desc) {
> > > > >                 dev_err(dev, "failed to prepare DMA descriptor\n");
> > > > > -               ret = PTR_ERR(desc);
> > > > > +               ret = -ENOMEM;
> > > >
> > > > Thank you for fixing this issue.
> > > > However, I believe -EIO is more appropriate than -ENOMEM, since
> > > > dmaengine_prep_slave_single() can return errors other than -ENOMEM.
> > > >
> > >
> > > It's not an I/O error so -EIO isn't correct.
> > >
> > > There are a bunch of reasons it could fail but most likely
> > > dma_pool_alloc() failed.  I think -ENOMEM is correct.
> > >
> >
> > Have you reviewed the implementation of ls1x_dma_prep_slave_sg()?
>
> The ls1x_dma_prep_slave_sg() has basically two error cases, buggy drivers
> and allocation errors.  Someone could argue that if people pass invalid
> data then the correct return is -EINVAL but in these cases it's a buggy
> driver and we fix bugs, we don't work around them.  So the correct
> return is -ENOMEM.
>

Yes, -EINVAL indicates a bug rather than a real error.
However, this assumes that the caller is aware they are providing invalid data.
Otherwise, they might be misled into thinking it is an out-of-memory
error (-ENOMEM).

> > Errors in this function can be caused not only by -ENOMEM, but also by -EINVAL.
> > Moreover, in most cases, the error handling logic for
> > dmaengine_prep_slave_single() returns -EIO when the function returns
> > NULL.
>
> There are some that return -EIO but hardly the majority.  Other places
> return -ENOMEM or -EINVAL.  It's not worth going back and fixing all of
> these but really -ENOMEM is the correct return.
>
> regards,
> dan carpenter
>

--
Best regards,

Keguang Zhang