i915/kms/backlight-combo mode problem (was: Re: Linux 2.6.39-rc5)

Commit Message

Takashi Iwai April 29, 2011, 7:47 p.m. UTC

At Fri, 29 Apr 2011 19:41:53 +0200,
Melchior FRANZ wrote:
> 
> * Takashi Iwai -- Friday 29 April 2011:
> > Melchior FRANZ wrote:
> > > The bug was introduced with commit ba3820ade317ee36e496b9b40d2ec3987dd4aef0
> > > [...] when using KMS my notebook's[2] screen remains dark, because the
> > > backlight isn't turned on.
> 
> > Could you check whether the patch below changes the behavior?
> > If this cures, it means that the backlight-combo mode doesn't work on
> > your machine.
> 
> Yes, that works. (Test was with fafc9929c668f8bae6dd1f109f33a86d2cb3c460,
> which is current HEAD.)

Looking at bugzilla, the problem seems like the case lbpc=0.
What about the patch below instead?


Takashi

---

Comments

Melchior FRANZ April 29, 2011, 8:09 p.m. UTC | #1

* Takashi Iwai -- Friday 29 April 2011:
[https://bugzilla.kernel.org/show_bug.cgi?id=31522]
> Looking at bugzilla, the problem seems like the case lbpc=0.
> What about the patch below instead?

> -			val *= lbpc;
> +			if (lbpc)
> +				val *= lbpc;

Yes, that works as well. (I had assumed that this was the problem,
but wasn't sure if a zero was even a legitimate value, or rather
a sign for a problem or wrong assumption elsewhere.)

m.

Patch

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index a06ff07..ba60218 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -207,7 +207,8 @@  u32 intel_panel_get_backlight(struct drm_device *dev)
 
 			val &= ~1;
 			pci_read_config_byte(dev->pdev, PCI_LBPC, &lbpc);
-			val *= lbpc;
+			if (lbpc)
+				val *= lbpc;
 		}
 	}