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Date:   Thu, 14 May 2020 23:55:36 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Enric Balletbo Serra <eballetbo@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Collabora Kernel ML <kernel@collabora.com>,
        Nicolas Boichat <drinkcat@chromium.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        David Airlie <airlied@linux.ie>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Hsin-Yi Wang <hsinyi@chromium.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v4 7/7] drm/mediatek: mtk_dsi: Create connector for
 bridges
Message-ID: <20200514205536.GN5955@pendragon.ideasonboard.com>
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Hi Enric,

On Thu, May 14, 2020 at 07:35:33PM +0200, Enric Balletbo i Serra wrote:
> On 14/5/20 19:12, Enric Balletbo i Serra wrote:
> > On 14/5/20 18:44, Chun-Kuang Hu wrote:
> >> Enric Balletbo i Serra <enric.balletbo@collabora.com> 於 2020年5月14日 週四 下午11:42寫道：
> >>> On 14/5/20 16:28, Chun-Kuang Hu wrote:
> >>>> Enric Balletbo Serra <eballetbo@gmail.com> 於 2020年5月14日 週四 上午12:41寫道：
> >>>>> Missatge de Enric Balletbo i Serra <enric.balletbo@collabora.com> 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@collabora.com>
> >>>>>> Acked-by: Sam Ravnborg <sam@ravnborg.org>
> >>>>>
> >>>>> 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.
> >>
> > 
> > I see, so yes, I am probably missing call drm_panel_attach in case there is a
> > direct panel attached. Thanks for pointing it.
> > 
> > I'll send a new version adding the drm_panel_attach call.
> > 
> 
> Wait, shouldn't panel be attached on the call of mtk_dsi_bridge_attach as
> next_bridge points to a bridge or a panel?
> 
> static int mtk_dsi_bridge_attach(struct drm_bridge *bridge,
> 				 enum drm_bridge_attach_flags flags)
> {
> 	struct mtk_dsi *dsi = bridge_to_dsi(bridge);
> 
> 	/* Attach the panel or bridge to the dsi bridge */
> 	return drm_bridge_attach(bridge->encoder, dsi->next_bridge,
> 				 &dsi->bridge, flags);
> }
> 
> Or I am continuing misunderstanding all this?

Panels should always be wrapped in a drm_bridge, so I think you're doing
right. I believe the call to drm_panel_attach() in omapdrm is a leftover
that can be removed. I'll have a look at it.

> >>>> 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.
> >>
> >>>>>> 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:

-- 
Regards,

Laurent Pinchart