Date:   Thu, 14 May 2020 19:35:33 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     Enric Balletbo Serra <eballetbo@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 7/7] drm/mediatek: mtk_dsi: Create connector for
 bridges

Hi again,

On 14/5/20 19:12, Enric Balletbo i Serra wrote:
> Hi Chun-Kuang,
> 
> On 14/5/20 18:44, Chun-Kuang Hu wrote:
>> Hi, Enric:
>>
>> Enric Balletbo i Serra <enric.balletbo@...labora.com> 於 2020年5月14日 週四 下午11:42寫道：
>>>
>>> Hi Chun-Kuang,
>>>
>>> On 14/5/20 16:28, Chun-Kuang Hu wrote:
>>>> Hi, Enric:
>>>>
>>>> Enric Balletbo Serra <eballetbo@...il.com> 於 2020年5月14日 週四 上午12:41寫道：
>>>>>
>>>>> Hi Chun-Kuang,
>>>>>
>>>>> Missatge de Enric Balletbo i Serra <enric.balletbo@...labora.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@...labora.com>
>>>>>> Acked-by: Sam Ravnborg <sam@...nborg.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?

>>>> 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
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Linux-mediatek mailing list
>>>>>> Linux-mediatek@...ts.infradead.org
>>>>>> http://lists.infradead.org/mailman/listinfo/linux-mediatek
> 

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