Re: [PATCH] drm: fix regression in fb blank handling

[Zhenyu Wang <zhenyuw@linux.intel.com>]

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On 2010.01.19 16:17:56 +0000, James Simmons wrote:
> Sorry I meant the backlight power management state seperate from the 
> encoder state.
>  
> > drm_fb_helper_off() will find fb's crtc and attached encoders, then
> > call encoder_funcs->dpms() and turn off crtc, so for your DRM_MODE_DPMS_ON
> > change, it will actually turn encoder on, but what we need for
> > FB_BLANK_NORMAL is to turn off the display. No?
> 
> FB_BLANK_NORMAL is not a full power down. Only CRTC is powerdown in this 
> mode.

So how the encoder could tell the meaning of you passed DRM_MODE_DPMS_ON in
this case? which is really turning on everything, or keep port on but turn
off panel power?

> FB_BLANK_POWERDOWN turns off everything. You are wondering why this 
> is the case. If the console blanks and you go to use it again it comes 
> back very fast. In FB_BLANK_POWERDOWN mode it takes awhile to come back 
> for certain types of displays. I have a old Sony CRT at home. Once powered 
> down it takes about 5 to 10 seconds to come back up.

Isn't this monitor specific issue instead of display device problem? ;)
I don't think any LCD monitor nowadays could have this issue.

> 
> Besides this the real issue is backlight != part of encoder. 
> 
> A patch will be coming shortly.

Panel power sequencing for Intel LVDS is controlled by encoder, and closely
related to port state, although we haven't really taken LVDS port enable/disable
step before Ironlake, I think this is normal case for encoders having backlight. 

Could we just restore back to origin behavior for fixing this in 2.6.33?
Otherwise I don't know if your patch would be too intrusive...

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