Hi Andrzej,
On Wed, Aug 04, 2021 at 04:09:38PM +0200, a.hajda wrote:
> Hi Maxime,
>
> I have been busy with other tasks, and I did not follow the list last
> time, so sorry for my late response.
>
> On 28.07.2021 15:32, Maxime Ripard wrote:
> > Hi,
> >
> > We've encountered an issue with the RaspberryPi DSI panel that prevented the
> > whole display driver from probing.
> >
> > The issue is described in detail in the commit 7213246a803f ("drm/vc4: dsi:
> > Only register our component once a DSI device is attached"), but the basic idea
> > is that since the panel is probed through i2c, there's no synchronization
> > between its probe and the registration of the MIPI-DSI host it's attached to.
> >
> > We initially moved the component framework registration to the MIPI-DSI Host
> > attach hook to make sure we register our component only when we have a DSI
> > device attached to our MIPI-DSI host, and then use lookup our DSI device in our
> > bind hook.
> >
> > However, all the DSI bridges controlled through i2c are only registering their
> > associated DSI device in their bridge attach hook, meaning with our change
>
> I guess this is incorrect. I have promoted several times the pattern
> that device driver shouldn't expose its interfaces (for example
> component_add, drm_panel_add, drm_bridge_add) until it gathers all
> required dependencies. In this particular case bridges should defer
> probe until DSI bus becomes available. I guess this way the patch you
> reverts would work.
>
> I advised few times this pattern in case of DSI hosts, apparently I
> didn't notice the similar issue can appear in case of bridges. Or there
> is something I have missed???
>
> Anyway there are already eleven(?) bridge drivers using this pattern. I
> wonder if fixing it would be difficult, or if it expose other issues???
> The patches should be quite straightforward - move
> of_find_mipi_dsi_host_by_node and mipi_dsi_device_register_full to probe
> time.
I gave this a try today, went back to the current upstream code and
found that indeed it works. I converted two bridges that works now. I'll
send a new version some time next week and will convert all the others
if we agree on the approach.
Thanks for the suggestion!
> Finally I think that if we will not fix these bridge drivers we will
> encounter another set of issues with new platforms connecting "DSI host
> drivers assuming this pattern" and "i2c/dsi device drivers assuming
> pattern already present in the bridges".
Yeah, this is exactly the situation I'm in :)
Maxime
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