DSI Bridge switching

[Laurent Pinchart]

Hello,

On Fri, Oct 08, 2021 at 03:27:43PM +0200, Andrzej Hajda wrote:
> Hi,
> 
> Removed my invalid email (I will update files next week).
> 
> On 08.10.2021 13:14, Jagan Teki wrote:
> > Hi,
> > 
> > I think this seems to be a known use case for industrial these days with i.mx8m.
> > 
> > The host DSI would configure with two bridges one for DSI to LVDS
> > (SN65DSI83) and another for DSI to HDMI Out (ADV7535). Technically we
> > can use only one bridge at a time as host DSI support single out port.
> > So we can have two separate device tree files for LVDS and HDMI and
> > load them static.
> > 
> > But, one of the use cases is to support both of them in single dts, and
> > - Turn On LVDS (default)
> > - Turn Off LVDS then Turn On HDMI when cable plug-in
> 
> Are you sure it will work from hardware PoV? Do you have some demuxer? 
> isolation of pins?

It may be in the category of "you shouldn't do this, but it actually
works". I've seen the same being done with two CSI-2 camera sensors
connected to the same receiver, with one of them being held in reset at
all times.

> > The HDMI event can be detected via some HDMI-INT GPIO on-board design.
> > 
> > The possible solution, I'm thinking of adding LVDS on port 1, HDMI on
> > port 2 in the DSI host node, and trying to attach the respective
> > bridge based on HDMI-INT like repeating the bridge attachment cycle
> > based on the HDMI-INT.
> 
> I think more appropriate would be to share the same port, but provide 
> two endpoints inside this port - we have two hardware sharing the same 
> physical port.

That sounds like the correct DT description to me.

> > Can it be possible to do bridge attachment at runtime? something like
> > a bridge hotplug event? or any other possible solutions?
> > 
> > Any suggestions?
> 
> Practically it is possible, see exynos_dsi + panels, or exynos_dsi + 
> some toshiba bridge - panel and bridge are dynamically 'plugged' and 
> 'unplugged' from exynos_drm, but they do not use bridge chain for this 
> and some other reasons. (un|re|)plugging should be performed of course 
> when pipeline is off (connector disconnected). I am not sure about 
> bridges added to bridge chain - you need to inspect all opses to ensure 
> it can be done safely.
> 
> And the main issue: Daniel does not like it :)

Neither do I :-) Could it be handled with two DRM connectors that are
mutually exclusive ?

-- 
Regards,

Laurent Pinchart