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

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Message-ID: <CAMuHMdUPhabZrXJ3UqSVTdy2aWf6VG27q287MizKJ5q5tyRnwA@mail.gmail.com>
Date:   Mon, 20 Jan 2020 13:05:09 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
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()

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);

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

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds