Re: [PATCH v7 05/10] drm: bridge: samsung-dsim: Add atomic_check

[Jagan Teki <jagan@amarulasolutions.com>]

On Mon, Oct 17, 2022 at 12:53 PM Marek Vasut <marex@denx.de> wrote:
>
> On 10/17/22 05:54, Jagan Teki wrote:
> > On Sun, Oct 16, 2022 at 2:53 AM Marek Vasut <marex@denx.de> wrote:
> >>
> >> On 10/5/22 17:13, Jagan Teki wrote:
> >>> Look like an explicit fixing up of mode_flags is required for DSIM IP
> >>> present in i.MX8M Mini/Nano SoCs.
> >>>
> >>> At least the LCDIF + DSIM needs active low sync polarities in order
> >>> to correlate the correct sync flags of the surrounding components in
> >>> the chain to make sure the whole pipeline can work properly.
> >>>
> >>> On the other hand the i.MX 8M Mini Applications Processor Reference Manual,
> >>> Rev. 3, 11/2020 says.
> >>> "13.6.3.5.2 RGB interface
> >>>    Vsync, Hsync, and VDEN are active high signals."
> >>>
> >>> No clear evidence about whether it can be documentation issues or
> >>> something, so added a comment FIXME for this and updated the active low
> >>> sync polarities using SAMSUNG_DSIM_TYPE_IMX8MM hw_type.
> >>
> >> [...]
> >>
> >>> +static int samsung_dsim_atomic_check(struct drm_bridge *bridge,
> >>> +                                  struct drm_bridge_state *bridge_state,
> >>> +                                  struct drm_crtc_state *crtc_state,
> >>> +                                  struct drm_connector_state *conn_state)
> >>> +{
> >>> +     struct samsung_dsim *dsi = bridge_to_dsi(bridge);
> >>> +     struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
> >>> +
> >>> +     if (dsi->plat_data->hw_type == SAMSUNG_DSIM_TYPE_IMX8MM) {
> >>> +             /**
> >>> +              * FIXME:
> >>> +              * At least LCDIF + DSIM needs active low sync,
> >>> +              * but i.MX 8M Mini Applications Processor Reference Manual,
> >>> +              * Rev. 3, 11/2020 says
> >>> +              *
> >>> +              * 13.6.3.5.2 RGB interface
> >>> +              * Vsync, Hsync, and VDEN are active high signals.
> >>> +              */
> >>> +             adjusted_mode->flags |= (DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC);
> >>> +             adjusted_mode->flags &= ~(DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
> >>> +     }
> >>
> >> It would be good to explain what exactly is going on here in the
> >> comment, the comment says "Vsync, Hsync, and VDEN are active high
> >> signals." and the code below does exact opposite and sets NxSYNC flags.
> >>
> >> Yes, the MX8MM/MN does need HS/VS/DE active LOW, it is a quirk of that
> >> MXSFB-DSIM glue logic. The MX8MP needs the exact opposite on all three,
> >> active HIGH.
> >
> > This is what exactly is mentioned in the comments.
> >
> > 2nd line mentioned the active low of signals.
> >>> +              * At least LCDIF + DSIM needs active low sync,
> >
> > from 3rd line onwards it mentioned what reference manual is referring
> >
> > Not quite understand what is misleading here.
>
> This part:
> "
> +  * Vsync, Hsync, and VDEN are active high signals.
> +  */
> +  adjusted_mode->flags |= (DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC);
> "
>
> Comment claims the signals are active high by quoting datasheet, and
> then sets the exact opposite on next line of code.

The comment stated what is done first and then gave the datasheet
reference. look this sequence seems confusing, I will recheck and
update the best possible comment.

>
> Have a look at this patch, I updated the comment there for MX8MP too:
> [PATCH] drm: bridge: samsung-dsim: Add i.MX8M Plus support

I will check.

Thanks,
Jagan.

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