Re: v3.10-rc1: backlight brightness after boot on N900

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 15/05/13 20:18, Aaro Koskinen wrote:
> Hi,
> 
> Is it expected that after boot you get 0 brightness i.e. a seemingly
> blank display on N900 with 3.10-rc1?
> 
> First thought after seeing a blank display was that the probe
> issues are still there, but everything was fine and after setting
> /sys/class/backlight/acx565akm/brightness you get a picture.
> 
> Just wondering how the initial brightness is determined anyway?

There were some small changes merged in v3.10 related to acx's
backlight, but they were removing dead code so I don't see how those
could affect...

Looking at the driver, the bl is initialized:

	if (md->has_bc)
		brightness = acx565akm_get_actual_brightness(md);
	else
		brightness = 0;

And has_bc is set only if the model is detected as MIPID_VER_ACX565AKM
(that's the panel in final N900, isn't it?). So what comes to my mind is
that either the model is detected wrong, or the
acx565akm_get_actual_brightness() which reads the current BL from the
panel happens to return 0, either because of an error, or because the
bootloader has set the BL to 0.

But why either of those would've changed with v3.10... No idea...

Can you add debug prints to see which code paths are taken there
(drivers/video/omap2/displays/panel-acx565akm.c, around line 580). The
panel model should also be printed with "omapfb: %s rev %02x LCD detected".

 Tomi



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