linux-kernel - Re: [PATCH] media: rcar_drif: Use dma_request_chan() instead dma_request_slave

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Date:   Mon, 20 Jan 2020 14:10:08 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Ramesh Shanmugasundaram <rashanmu@...il.com>,
        Vinod <vkoul@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] media: rcar_drif: Use dma_request_chan() instead
 dma_request_slave_channel()

Hi Geert,

On 20/01/2020 14.05, Geert Uytterhoeven wrote:
> On Tue, Dec 17, 2019 at 11:41 AM Peter Ujfalusi <peter.ujfalusi@...com> wrote:
>> dma_request_slave_channel() is a wrapper on top of dma_request_chan()
>> eating up the error code.
>>
>> By using dma_request_chan() directly the driver can support deferred
>> probing against DMA.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> One comment below.
> 
>> --- a/drivers/media/platform/rcar_drif.c
>> +++ b/drivers/media/platform/rcar_drif.c
>> @@ -275,10 +275,10 @@ static int rcar_drif_alloc_dmachannels(struct rcar_drif_sdr *sdr)
>>         for_each_rcar_drif_channel(i, &sdr->cur_ch_mask) {
>>                 struct rcar_drif *ch = sdr->ch[i];
>>
>> -               ch->dmach = dma_request_slave_channel(&ch->pdev->dev, "rx");
>> -               if (!ch->dmach) {
>> +               ch->dmach = dma_request_chan(&ch->pdev->dev, "rx");
>> +               if (IS_ERR(ch->dmach)) {
>>                         rdrif_err(sdr, "ch%u: dma channel req failed\n", i);
> 
> Now there is an error code, you might (1) want to print it, and (2) only
> do so when it is not due to probe deferral:
> 
>         if (PTR_ERR(ch->dmach) != -EPROBE_DEFER)
>                 rdrif_err(sdr, "ch%u: dma channel req failed %pe\n",
> i, ch->dmach);

Yes, this is true.

> 
>> -                       ret = -ENODEV;
>> +                       ret = PTR_ERR(ch->dmach);

if (ret != -EPROBE_DEFER)
	rdrif_err(sdr, "ch%u: dma channel req failed (%d)\n", i, ret);

might be simpler.

>>                         goto dmach_error;
>>                 }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

- Péter

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