linux-kernel - Re: [28/39] drm: renesas: shmobile: Use drm_crtc_handle

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Message-ID: <CAMuHMdX8=16pRQr=2CouUWBUhD16Mkh3_WaNZmRTd7Wjwq_pnw@mail.gmail.com>
Date:   Sun, 25 Jun 2023 10:55:56 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sui Jingfeng <suijingfeng@...ngson.cn>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Magnus Damm <magnus.damm@...il.com>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [28/39] drm: renesas: shmobile: Use drm_crtc_handle_vblank()

Hi Sui,

On Sat, Jun 24, 2023 at 11:33 AM Sui Jingfeng <suijingfeng@...ngson.cn> wrote:
> I'm fine with this patch but I I don't see the benefit.
>
> This reply is more about my personal question.
>
> On 2023/6/22 17:21, Geert Uytterhoeven wrote:
> > Replace the call to the legacy drm_handle_vblank() function with a call
> > to the new drm_crtc_handle_vblank() helper.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> Reviewed-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> > ---
> >   drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
> > index c98e2bdd888c3274..6eaf2c5a104f451a 100644
> > --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
> > +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
> > @@ -86,7 +86,7 @@ static irqreturn_t shmob_drm_irq(int irq, void *arg)
> >       spin_unlock_irqrestore(&sdev->irq_lock, flags);
> >
> >       if (status & LDINTR_VES) {
> > -             drm_handle_vblank(dev, 0);
> > +             drm_crtc_handle_vblank(&sdev->crtc.base);
>
>
> After switching to drm_crtc_handle_vblank(),
>
> your driver need another deference to the pointer of 'struct drm_crtc'
> to get the pointer of 'struct drm_device';
>
> Plus another call to get the index(display pipe) of the CRTC by calling
> drm_crtc_index(crtc).

That is correct.

> Consider that shmob-drm support only one display pipe,
>
> is it that the switching is less straight forward than the original
> implement ?
>
>
> ```
>
> /**
>   * drm_crtc_handle_vblank - handle a vblank event
>   * @crtc: where this event occurred
>   *
>   * Drivers should call this routine in their vblank interrupt handlers to
>   * update the vblank counter and send any signals that may be pending.
>   *
>   * This is the native KMS version of drm_handle_vblank().
>   *
>   * Note that for a given vblank counter value drm_crtc_handle_vblank()
>   * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time()
>   * provide a barrier: Any writes done before calling
>   * drm_crtc_handle_vblank() will be visible to callers of the later
>   * functions, if the vblank count is the same or a later one.
>   *
>   * See also &drm_vblank_crtc.count.
>   *
>   * Returns:
>   * True if the event was successfully handled, false on failure.
>   */
> bool drm_crtc_handle_vblank(struct drm_crtc *crtc)
> {
>      return drm_handle_vblank(crtc->dev, drm_crtc_index(crtc));
> }
>
> ```
>
> Is it that drm_crtc_handle_vblank() function is preferred over
> drm_handle_vblank() in the future?
>
> I'm fine with this question answered.

I think the native KMS version is preferred over the legacy version, cfr.

    /**
     * drm_handle_vblank - handle a vblank event
    [...]
     * This is the legacy version of drm_crtc_handle_vblank().
     */
    bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe)

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