linux-kernel - Re: [PATCH] drm/bridge: panel: Set orientation on panel

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Message-ID: <Y856rWmtA4tQCcZz@donbot>
Date:   Mon, 23 Jan 2023 12:16:45 +0000
From:   John Keeping <john@...anate.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Sam Ravnborg <sam@...nborg.org>,
        Doug Anderson <dianders@...omium.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Stephen Boyd <swboyd@...omium.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH] drm/bridge: panel: Set orientation on panel_bridge
 connector

Hi Laurent,

On Sun, Jan 22, 2023 at 05:01:27PM +0200, Laurent Pinchart wrote:
> On Sat, Jan 21, 2023 at 05:58:11PM +0000, John Keeping wrote:
> > On Sat, Jan 21, 2023 at 09:57:18AM +0100, Sam Ravnborg wrote:
> > > On Fri, Jan 20, 2023 at 01:44:38PM -0800, Doug Anderson wrote:
> > > > On Fri, Jan 20, 2023 at 3:43 AM John Keeping wrote:
> > > > >
> > > > > Commit 15b9ca1641f0 ("drm: Config orientation property if panel provides
> > > > > it") added a helper to set the panel panel orientation early but only
> > > > > connected this for drm_bridge_connector, which constructs a panel bridge
> > > > > with DRM_BRIDGE_ATTACH_NO_CONNECTOR and creates the connector itself.
> > > > >
> > > > > When the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is not specified and the
> > > > > panel_bridge creates its own connector the orientation is not set unless
> > > > > the panel does it in .get_modes which is too late and leads to a warning
> > > > > splat from __drm_mode_object_add() because the device is already
> > > > > registered.
> > > > >
> > > > > Call the necessary function to set add the orientation property when the
> > > > > connector is created so that it is available before the device is
> > > > > registered.
> > > > 
> > > > I have no huge objection to your patch and it looks OK to me. That
> > > > being said, my understanding is that:
> > > > 
> > > > 1. DRM_BRIDGE_ATTACH_NO_CONNECTOR is "the future" and not using the
> > > > flag is "deprecated".
> > >
> > > Correct.
> > > Could we take a look at how much is required to move the relevant driver
> > > to use DRM_BRIDGE_ATTACH_NO_CONNECTOR?
> > >
> > > If this is too much work now we may land this simple patch, but the
> > > preference is to move all drivers to the new bridge handling and thus
> > > asking display drivers to create the connector.
> 
> I fully agree with Doug and Sam here. Let's see if we can keep the yak
> shaving minimal :-)
> 
> > > What display driver are we dealing with here?
> > 
> > This is dw-mipi-dsi-rockchip which uses the component path in
> > dw-mipi-dsi (and, in fact, is the only driver using that mode of
> > dw-mipi-dsi).
> > 
> > I'm not familiar enough with DRM to say whether it's easy to convert to
> > DRM_BRIDGE_ATTACH_NO_CONNECTOR - should dw-mipi-dsi-rockchip be moving
> > to use dw-mipi-dsi as a bridge driver or should dw_mipi_dsi_bind() have
> > a drm_bridge_attach_flags argument?  But I'm happy to test patches if it
> > looks easy to convert to you :-)
> 
> I'd go for the former (use dw_mipi_dsi_probe() and acquire the DSI
> bridge with of_drm_find_bridge() instead of using the component
> framework) if possible, but I don't know how intrusive that would be.

I'm a bit confused about what's required since dw-mipi-dsi-rockchip
already uses dw_mipi_dsi_probe(), but I think moving away from the
component framework would be significant work as that's how the MIPI
subdriver fits in to the overall Rockchip display driver.

Any changes / modernisation to the Rockchip MIPI driver look like it
will take more time than I have available to spend on this, so I'd
really like to see this patch land as it's a simple fix to an existing
working code path.


John