Re: [PATCH 05/13] drm/i915: fix gen2-gen3 backlight set

[Imre Deak <imre.deak@intel.com>]

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On Wed, 2013-11-13 at 10:27 +0200, Jani Nikula wrote:
> On Wed, 13 Nov 2013, Imre Deak <imre.deak@intel.com> wrote:
> > On Fri, 2013-11-08 at 16:48 +0200, Jani Nikula wrote:
> >> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> ---
> >>  drivers/gpu/drm/i915/intel_panel.c |   10 +++++++---
> >>  1 file changed, 7 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> >> index a821949..e82b2dd 100644
> >> --- a/drivers/gpu/drm/i915/intel_panel.c
> >> +++ b/drivers/gpu/drm/i915/intel_panel.c
> >> @@ -555,7 +555,7 @@ static void i9xx_set_backlight(struct intel_connector *connector, u32 level)
> >>  {
> >>  	struct drm_device *dev = connector->base.dev;
> >>  	struct drm_i915_private *dev_priv = dev->dev_private;
> >> -	u32 tmp;
> >> +	u32 tmp, mask;
> >>  
> >>  	if (is_backlight_combination_mode(dev)) {
> >>  		u32 max = intel_panel_get_max_backlight(connector);
> >> @@ -570,10 +570,14 @@ static void i9xx_set_backlight(struct intel_connector *connector, u32 level)
> >>  		pci_write_config_byte(dev->pdev, PCI_LBPC, lbpc);
> >>  	}
> >>  
> >> -	if (INTEL_INFO(dev)->gen < 4)
> >> +	if (IS_GEN4(dev)) {
> >> +		mask = BACKLIGHT_DUTY_CYCLE_MASK;
> >> +	} else {
> >>  		level <<= 1;
> >> +		mask = BACKLIGHT_DUTY_CYCLE_MASK_PNV;
> >> +	}
> >
> > According to the gen2/3 bspec I have, the correct mask is
> > BACKLIGHT_DUTY_CYCLE_MASK_PNV only in case of IS_PINEVIEW(dev), for
> > everything else it's BACKLIGHT_DUTY_CYCLE_MASK.
> 
> What you say is correct, but we've treated all gen2/3 similar to PNV
> since
> 
> commit ca88479c1c3b7b1a9f94320745f5331e1de77f80
> Author: Keith Packard <keithp@keithp.com>
> Date:   Fri Nov 18 11:09:24 2011 -0800
> 
>     drm/i915: Treat pre-gen4 backlight duty cycle value consistently
> 
> i.e. we only use the high 15 bits for all gen2/3. For non-PNV this just
> means the lowest bit is always zero. For PNV the lowest bit has a
> different meaning in both the PWM freq and duty cycle fields.
> 
> I don't want to take any chances by changing this behaviour. I realize
> there's zero comments about this in the code; would you like me to add
> some?

Yea, looking at the log would've been useful.. I see now from that
commit that there was a problem with setting bit 0 on some old HW, so
I'm ok to leave this as-is. A comment would be nice, but either way:

Reviewed-by: Imre Deak <imre.deak@intel.com>


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