linux-kernel - Re: i915/kms/backlight-combo mode problem

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Message-ID: <86bopwk7r7.fsf@sumi.keithp.com>
Date:	Sat, 21 Jan 2012 14:31:24 -0800
From:	Keith Packard <keithp@...thp.com>
To:	Chris Diamand <chris.diamand@...il.com>
Cc:	linux-kernel@...r.kernel.org, tiwai@...e.de,
	melchior.franz@...il.com
Subject: Re: i915/kms/backlight-combo mode problem

On Sat, 21 Jan 2012 21:25:56 +0000, Chris Diamand <chris.diamand@...il.com> wrote:

> 0x00 is the brightest. It gets very gradually dimmer up to about 0xB0, 
> when the gaps between
> brightness levels are slightly bigger.
> 0xFE is very low but still works.
> Barely any difference between 0x80 and 0x7f, same with 0x00 and 0x01,
> etc.

Here's a patch which just flips the interpretation of that value over;
does this work?

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 04d79fd..43faa9d 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -207,6 +207,7 @@ u32 intel_panel_get_backlight(struct drm_device *dev)
                        u8 lbpc;
 
                        pci_read_config_byte(dev->pdev, PCI_LBPC, &lbpc);
+                       lbpc = 0xff - lbpc;
                        val *= lbpc;
                }
        }
@@ -238,7 +239,7 @@ static void intel_panel_actually_set_backlight(struct drm_device *dev, u32 level
 
                lbpc = level * 0xfe / max + 1;
                level /= lbpc;
-               pci_write_config_byte(dev->pdev, PCI_LBPC, lbpc);
+               pci_write_config_byte(dev->pdev, PCI_LBPC, 0xff - lbpc);
        }
 
        tmp = I915_READ(BLC_PWM_CTL);


-- 
keith.packard@...el.com

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