Re: [PATCH v4 7/7] drm/mediatek: mtk_dsi: Create connector for bridges

[Chun-Kuang Hu]

Hi, Enric:

Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx> æ 2020å5æ14æ éå äå11:42åéï
>
> Hi Chun-Kuang,
>
> On 14/5/20 16:28, Chun-Kuang Hu wrote:
> > Hi, Enric:
> >
> > Enric Balletbo Serra <eballetbo@xxxxxxxxx> æ 2020å5æ14æ éå äå12:41åéï
> >>
> >> Hi Chun-Kuang,
> >>
> >> Missatge de Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx> del
> >> dia dv., 1 de maig 2020 a les 17:25:
> >>>
> >>> Use the drm_bridge_connector helper to create a connector for pipelines
> >>> that use drm_bridge. This allows splitting connector operations across
> >>> multiple bridges when necessary, instead of having the last bridge in
> >>> the chain creating the connector and handling all connector operations
> >>> internally.
> >>>
> >>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> >>> Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
> >>
> >> A gentle ping on this, I think that this one is the only one that
> >> still needs a review in the series.
> >
> > This is what I reply in patch v3:
> >
>
> Sorry for missing this.
>
> > I think the panel is wrapped into next_bridge here,
> >
>
> Yes, you can have for example:
>
> 1. drm_bridge (mtk_dsi) -> drm_bridge (ps8640 - dsi-to-edp) -> drm_panel_bridge
> (edp panel)
>
> or a
>
> 2. drm_bridge (mtk_dsi)-> drm_panel_bridge (dsi panel)
>
> The _first_ one is my use case
>
> > if (panel) {
>
> This handles the second case, where you attach a dsi panel.
>
> >     dsi->next_bridge = devm_drm_panel_bridge_add(dev, panel);
> >
> > so the next_bridge is a panel_bridge, in its attach function
> > panel_bridge_attach(),
> > according to the flag DRM_BRIDGE_ATTACH_NO_CONNECTOR, if not exist,
> > it would create connector and attach connector to panel.
> >
> > I'm not sure this flag would exist or not, but for both case, it's strange.
> > If exist, you create connector in this patch but no where to attach
> > connector to panel.
>
> Yes, in fact, this is transitional patch needed, as once I converted mtk_dpi,
> mtk_dsi and mtk_hdmi to the new drm_bridge API the drm_bridge_connector_init()
> will be done in mtk_drm_drv. We will need to call drm_bridge_connector_init for
> dpi and dsi pipes and remove that call from mtk_dsi and mtk_dpi drivers. The
> graphic controller driver should create connectors and CRTCs, as example you can
> take a look at drivers/gpu/drm/omapdrm/omap_drv.c
>

I have such question because I've reviewed omap's driver. In omap's
driver, after it call drm_bridge_connector_init(), it does this:

if (pipe->output->panel) {
ret = drm_panel_attach(pipe->output->panel,
      pipe->connector);
if (ret < 0)
return ret;
}

In this patch, you does not do this.

> > If not exist, the next_brige would create one connector and this brige
> > would create another connector.
> >
> > I think in your case, mtk_dsi does not directly connect to a panel, so
>
> Exactly
>
> > I need a exact explain. Or someone could test this on a
> > directly-connect-panel platform.
>
> I don't think I am breaking this use case but AFAICS there is no users in
> mainline that directly connect a panel using the mediatek driver. As I said my
> use case is the other so I can't really test. Do you know anyone that can test this?

I'm not sure who can test this, but [1], which is sent by YT Shen in a
series, is a patch to support dsi command mode so dsi could directly
connect to panel.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/mediatek?h=v5.7-rc5&id=21898816831fc60c92dd634ab4316a24da7eb4af

It's better that someone could test this case, but if no one would
test this, I could also accept a good-look patch.

Regards,
Chun-Kuang.

>
> Thanks,
>  Enric
>
> >
> > Regards,
> > Chun-Kuang.
> >
> >>
> >> Thanks,
> >>  Enric
> >>
> >>> ---
> >>>
> >>> Changes in v4: None
> >>> Changes in v3:
> >>> - Move the bridge.type line to the patch that adds drm_bridge support. (Laurent Pinchart)
> >>>
> >>> Changes in v2: None
> >>>
> >>>  drivers/gpu/drm/mediatek/mtk_dsi.c | 13 ++++++++++++-
> >>>  1 file changed, 12 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> >>> index 4f3bd095c1ee..471fcafdf348 100644
> >>> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> >>> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> >>> @@ -17,6 +17,7 @@
> >>>
> >>>  #include <drm/drm_atomic_helper.h>
> >>>  #include <drm/drm_bridge.h>
> >>> +#include <drm/drm_bridge_connector.h>
> >>>  #include <drm/drm_mipi_dsi.h>
> >>>  #include <drm/drm_of.h>
> >>>  #include <drm/drm_panel.h>
> >>> @@ -183,6 +184,7 @@ struct mtk_dsi {
> >>>         struct drm_encoder encoder;
> >>>         struct drm_bridge bridge;
> >>>         struct drm_bridge *next_bridge;
> >>> +       struct drm_connector *connector;
> >>>         struct phy *phy;
> >>>
> >>>         void __iomem *regs;
> >>> @@ -977,10 +979,19 @@ static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
> >>>          */
> >>>         dsi->encoder.possible_crtcs = 1;
> >>>
> >>> -       ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL, 0);
> >>> +       ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
> >>> +                               DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> >>>         if (ret)
> >>>                 goto err_cleanup_encoder;
> >>>
> >>> +       dsi->connector = drm_bridge_connector_init(drm, &dsi->encoder);
> >>> +       if (IS_ERR(dsi->connector)) {
> >>> +               DRM_ERROR("Unable to create bridge connector\n");
> >>> +               ret = PTR_ERR(dsi->connector);
> >>> +               goto err_cleanup_encoder;
> >>> +       }
> >>> +       drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
> >>> +
> >>>         return 0;
> >>>
> >>>  err_cleanup_encoder:
> >>> --
> >>> 2.26.2
> >>>
> >>>
> >>> _______________________________________________
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