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

[Jani Nikula <jani.nikula@intel.com>]

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?


BR,
Jani.


>
> --Imre
>
>>  
>> -	tmp = I915_READ(BLC_PWM_CTL) & ~BACKLIGHT_DUTY_CYCLE_MASK;
>> +	tmp = I915_READ(BLC_PWM_CTL) & ~mask;
>>  	I915_WRITE(BLC_PWM_CTL, tmp | level);
>>  }
>>  
>
>

-- 
Jani Nikula, Intel Open Source Technology Center