linux-kernel - Re: [PATCH v5 2/6] drm: lcdif: Drop unnecessary NULL pointer check on lcdif->bridge

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Message-ID: <CAOcKUNXjvOMXtf2FVwjhWNbdwQy82T+wz-QN7ukAOmQo5DKQ2w@mail.gmail.com>
Date:   Wed, 10 May 2023 16:30:32 +0800
From:   Ying Liu <gnuiyl@...il.com>
To:     Marek Vasut <marex@...x.de>
Cc:     Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, conor+dt@...nel.org,
        alexander.stein@...tq-group.com, shawnguo@...nel.org,
        s.hauer@...gutronix.de, krzysztof.kozlowski@...aro.org,
        robh+dt@...nel.org, linux-imx@....com,
        krzysztof.kozlowski+dt@...aro.org, kernel@...gutronix.de,
        LW@...o-electronics.de
Subject: Re: [PATCH v5 2/6] drm: lcdif: Drop unnecessary NULL pointer check on lcdif->bridge

On Tue, May 9, 2023 at 10:14 AM Marek Vasut <marex@...x.de> wrote:
>
> On 5/8/23 07:57, Liu Ying wrote:
>
> Hi,

Hi,

>
> > diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> > index 262bc43b1079..e54200a9fcb9 100644
> > --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
> > +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> > @@ -394,7 +394,7 @@ static void lcdif_crtc_mode_set_nofb(struct lcdif_drm_private *lcdif,
> >       struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode;
> >       u32 bus_flags = 0;
> >
> > -     if (lcdif->bridge && lcdif->bridge->timings)
> > +     if (lcdif->bridge->timings)
> >               bus_flags = lcdif->bridge->timings->input_bus_flags;
> >       else if (bridge_state)
> >               bus_flags = bridge_state->input_bus_cfg.flags;
> > @@ -463,30 +463,21 @@ static void lcdif_crtc_atomic_enable(struct drm_crtc *crtc,
> >       struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode;
> >       struct drm_bridge_state *bridge_state = NULL;
> >       struct drm_device *drm = lcdif->drm;
> > -     u32 bus_format = 0;
> > +     u32 bus_format;
> >       dma_addr_t paddr;
> >
> > -     /* If there is a bridge attached to the LCDIF, use its bus format */
> > -     if (lcdif->bridge) {
> > -             bridge_state =
> > -                     drm_atomic_get_new_bridge_state(state,
> > -                                                     lcdif->bridge);
> > -             if (!bridge_state)
> > -                     bus_format = MEDIA_BUS_FMT_FIXED;
> > -             else
> > -                     bus_format = bridge_state->input_bus_cfg.format;
> > -
> > -             if (bus_format == MEDIA_BUS_FMT_FIXED) {
> > -                     dev_warn_once(drm->dev,
> > -                                   "Bridge does not provide bus format, assuming MEDIA_BUS_FMT_RGB888_1X24.\n"
> > -                                   "Please fix bridge driver by handling atomic_get_input_bus_fmts.\n");
> > -                     bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> > -             }
> > -     }
> > +     bridge_state = drm_atomic_get_new_bridge_state(state, lcdif->bridge);
> > +     if (!bridge_state)
> > +             bus_format = MEDIA_BUS_FMT_FIXED;
> > +     else
> > +             bus_format = bridge_state->input_bus_cfg.format;
>
> The code below seems to change the logic slightly.
>
> Could it happen that:
> - bridge_state is valid (i.e. non-NULL)
> - bridge_state->input_bus_cfg.format is set to 0 (i.e. not set) ?
>    (note that MEDIA_BUS_FMT_FIXED is defined as 0x0001)

Yes, bridge_state->input_bus_cfg.format could be zero.
Will keep the below default MEDIA_BUS_FMT_RGB888_1X24
bus format setting in next version.

Regards,
Liu Ying

>
> > -     /* If all else fails, default to RGB888_1X24 */
> > -     if (!bus_format)
> > +     if (bus_format == MEDIA_BUS_FMT_FIXED) {
> > +             dev_warn_once(drm->dev,
> > +                           "Bridge does not provide bus format, assuming MEDIA_BUS_FMT_RGB888_1X24.\n"
> > +                           "Please fix bridge driver by handling atomic_get_input_bus_fmts.\n");
> >               bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> > +     }
> >
> >       clk_set_rate(lcdif->clk, m->crtc_clock * 1000);
>
> [...]