How to use backlight device with fb device

How to use backlight device with fb device

[Tomi Valkeinen]

Hi,

I'm a bit confused how a backlight device and a fb device should be
"connected".

In this particular case the OMAP 4430SDP board has an LCD panel
controlled by omapfb (and omapdss on the lower level) with a backlight
controlled by pwm_backlight (and twl6030-pwm on the lower level).

Both omapfb and pwm_backlight work fine, but they don't know anything
about each other, so, for example, blanking the fb via omapfb leaves the
backlight on.

Is there something I'm missing, or is the only solution to have some
custom code to connect the fb and the bl, and handle it that way?

 Tomi

Re: How to use backlight device with fb device

[Florian Tobias Schandinat]

Hi Tomi,

On 09/15/2011 07:47 AM, Tomi Valkeinen wrote:
> Hi,
> 
> I'm a bit confused how a backlight device and a fb device should be
> "connected".
> 
> In this particular case the OMAP 4430SDP board has an LCD panel
> controlled by omapfb (and omapdss on the lower level) with a backlight
> controlled by pwm_backlight (and twl6030-pwm on the lower level).
> 
> Both omapfb and pwm_backlight work fine, but they don't know anything
> about each other, so, for example, blanking the fb via omapfb leaves the
> backlight on.
> 
> Is there something I'm missing, or is the only solution to have some
> custom code to connect the fb and the bl, and handle it that way?

I don't know anything about backlight but recently there was a patch that
affected the same area you mention so it might give an idea
"[PATCH] FB: add early fb blank feature."
http://marc.info/?l=linux-fbdev&m\x131554458720940&w=2


Best regards,

Florian Tobias Schandinat

> 
>  Tomi
> 
> 
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Re: How to use backlight device with fb device

[Tomi Valkeinen]

On Thu, 2011-09-15 at 08:58 +0000, Florian Tobias Schandinat wrote:
> Hi Tomi,
> 
> On 09/15/2011 07:47 AM, Tomi Valkeinen wrote:
> > Hi,
> > 
> > I'm a bit confused how a backlight device and a fb device should be
> > "connected".
> > 
> > In this particular case the OMAP 4430SDP board has an LCD panel
> > controlled by omapfb (and omapdss on the lower level) with a backlight
> > controlled by pwm_backlight (and twl6030-pwm on the lower level).
> > 
> > Both omapfb and pwm_backlight work fine, but they don't know anything
> > about each other, so, for example, blanking the fb via omapfb leaves the
> > backlight on.
> > 
> > Is there something I'm missing, or is the only solution to have some
> > custom code to connect the fb and the bl, and handle it that way?
> 
> I don't know anything about backlight but recently there was a patch that
> affected the same area you mention so it might give an idea
> "[PATCH] FB: add early fb blank feature."
> http://marc.info/?l=linux-fbdev&m\x131554458720940&w=2

Ah, thanks for pointing that out.

I seem to have dropped from linux-fbdev list and hadn't received that
post. For some reason I seem to get dropped from linux mailing lists,
this is getting a bit frustrating...

 Tomi