linux-kernel - Re: [PATCH 3/3] spi: rockchip: check requesting dma channel with EPROBE

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Date:	Tue, 22 Mar 2016 14:59:56 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Shawn Lin <shawn.lin@...k-chips.com>,
	Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH 3/3] spi: rockchip: check requesting dma channel with
 EPROBE_DEFER

On Mon, Mar 21, 2016 at 04:33:32PM -0700, Doug Anderson wrote:
> Presumably Dan would be happy if you just add this right after the dev_warn():
>   rs->dma_tx.ch = NULL;
> 

Yes.  Thanks.

> Presumably from Dan's email it would also be wise to make sure you
> don't pass NULL to PTR_ERR, which you could probably do by just using
> ERR_PTR instead of PTR_ERR.  I think you could structure like this:
> 
>         rs->dma_tx.ch = dma_request_slave_channel(rs->dev, "tx");
> -       if (!rs->dma_tx.ch)
> +       if (IS_ERR_OR_NULL(rs->dma_tx.ch)) {
> +               /* Check tx to see if we need defer probing driver */
> +               if (rs->dma_tx.ch == ERR_PTR(-EPROBE_DEFER)) {
> +                       ret = -EPROBE_DEFER;
> +                       goto err_get_fifo_len;
> +               }
>                 dev_warn(rs->dev, "Failed to request TX DMA channel\n");
> +               rs->dma_tx.ch = NULL;
> +       }

My check doesn't care if you pass something to PTR_ERR() that might be
NULL, it complains when PTR_ERR() can only be zero.  And it's ok to have
the warning for a while and silence it in another patch when we update
dma_request_slave_channel().

But this also works well.

regards,
dan carpenter