[BISECTED, REGRESSION] v4.12-rc: omapdrm fails to probe on Nokia N900

[Peter Ujfalusi]

On 2017-06-15 01:11, Aaro Koskinen wrote:
> Hi,
> 
> When booting v4.12-rc5 on Nokia N900, omapdrm fails to probe and there
> is no display.
> 
> Bisected to:
> 
> a09d2bc1503508c17ef3a71c6b1905e3660f3029 is the first bad commit
> commit a09d2bc1503508c17ef3a71c6b1905e3660f3029
> Author: Peter Ujfalusi <peter.ujfalusi at ti.com>
> Date:   Tue May 3 22:08:01 2016 +0300
> 
>     drm/omap: Use omapdss_stack_is_ready() to check that the display stack is up
>     
>     Instead of 'guessing' based on aliases of the status of the DSS drivers,
>     use the new interface to check that all needed drivers are loaded.
>     In this way we can be sure that all needed drivers are loaded so it is
>     safe to continue the probing of omapdrm.
>     This method will allow the omapdrm to be probed 'headless', without
>     outputs.
>     
>     Signed-off-by: Peter Ujfalusi <peter.ujfalusi at ti.com>
>     Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> 
> Reverting the commit seems to fix the issue.

When you revert this patch do you see a warning saying:
"could not connect display: blah" ? if so what is 'blah'?

n900 have two displays afaik, LCD and TVout. omapdss_stack_is_ready() is
to ensure that we have all the drivers loaded for both displays, while
by reverting it it is enough if one of them is loaded at the time we do
the check and omapdrm would continue to probe, but the missing display
(even if it is going to be probed a bit later) will not work.

- Péter