linux-kernel - Re: [PATCH v3 7/7] drm/mediatek: mtk

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Date:   Sat, 2 May 2020 09:54:15 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v3 7/7] drm/mediatek: mtk_dsi: Create connector for bridges

Hi, Enric:

Enric Balletbo i Serra <enric.balletbo@...labora.com> 於 2020年5月1日 週五 下午10:59寫道：
>
> Hi Chun-Kuang,
>
> Thank you for your review.
>
> On 1/5/20 16:26, Chun-Kuang Hu wrote:
> > Hi, Enric:
> >
> > Enric Balletbo i Serra <enric.balletbo@...labora.com> 於 2020年4月17日 週五 下午11:06寫道：
> >>
> >> 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@...labora.com>
> >> ---
> >>
> >> 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 157097c63b23..85f76b01ae4d 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);
> >> +
> >
> > I'm not very clear about how brige-connector works, but why connector
> > does not attach to panel?
> >
>
> Laurent or other drm maintainers might have more details than me, but, AFAIK the
> drm_bridge_connector_init initializes a connector for a chain of bridges that
> starts at the @encoder. At this point you don't know which bridge is connected
> to the panel physically but doesn't really matter as what you know is that will
> be only one connector in the  chain.

I think the panel is wrapped into next_bridge here,

if (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.
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
I need a exact explain. Or someone could test this on a
directly-connect-panel platform.

Regards,
Chun-Kuang.

>
> Thanks,
>  Enric
>
> > Regards,
> > Chun-Kuang.
> >
> >>         return 0;
> >>
> >>  err_cleanup_encoder:
> >> --
> >> 2.25.1
> >>