[PATCH] drivers: i915: Default max backlight brightness value

[PATCH] drivers: i915: Default max backlight brightness value

[Simon Que]

In the native backlight driver, use 4096 (0x1000) as the default backlight
period, and use the period as the default max brightness.

The default brightness is defined in a separate function that can be
expanded to allow for different defaults on different systems in the
future.

Change-Id: Ie783b53dd034dcd7bf42e24ffc911cf2f10a5676
Signed-off-by: Simon Que <sque@chromium.org>
---
 drivers/gpu/drm/i915/i915_reg.h    |    1 +
 drivers/gpu/drm/i915/intel_panel.c |   22 ++++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 5d5def7..a832028 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3275,6 +3275,7 @@
 #define  PWM_POLARITY_ACTIVE_HIGH2	(0 << 28)
 
 #define BLC_PWM_PCH_CTL2	0xc8254
+#define BLC_PWM_PCH_FREQ_SHIFT	16
 
 #define PCH_PP_STATUS		0xc7200
 #define PCH_PP_CONTROL		0xc7204
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 05f500c..8205945 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -161,6 +161,12 @@ static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
 	return val;
 }
 
+static u32 intel_panel_get_default_backlight_period(struct drm_device *dev)
+{
+	/* The default number of clock cycles in one backlight PWM period. */
+	return 0x1000;
+}
+
 u32 intel_panel_get_max_backlight(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -168,11 +174,19 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
 
 	max = i915_read_blc_pwm_ctl(dev_priv);
 	if (max == 0) {
-		/* XXX add code here to query mode clock or hardware clock
-		 * and program max PWM appropriately.
+		/* If no max backlight was found, use the default PWM period as
+		 * the max backlight value.
 		 */
-		printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
-		return 1;
+		max = intel_panel_get_default_backlight_period(dev);
+		if (HAS_PCH_SPLIT(dev_priv->dev)) {
+			u32 val = max << BLC_PWM_PCH_FREQ_SHIFT;
+			I915_WRITE(BLC_PWM_PCH_CTL2, val);
+		} else {
+			u32 val = max << BACKLIGHT_MODULATION_FREQ_SHIFT;
+			I915_WRITE(BLC_PWM_CTL, val);
+		}
+
+		return max;
 	}
 
 	if (HAS_PCH_SPLIT(dev)) {
-- 
1.7.2.3

Re: [PATCH] drivers: i915: Default max backlight brightness value

[Simon Que]

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Hi, could I get some feedback on this patch, please?

Simon

On Fri, Oct 14, 2011 at 4:46 PM, Simon Que <sque@chromium.org> wrote:

> In the native backlight driver, use 4096 (0x1000) as the default backlight
> period, and use the period as the default max brightness.
>
> The default brightness is defined in a separate function that can be
> expanded to allow for different defaults on different systems in the
> future.
>
> Change-Id: Ie783b53dd034dcd7bf42e24ffc911cf2f10a5676
> Signed-off-by: Simon Que <sque@chromium.org>
> ---
>  drivers/gpu/drm/i915/i915_reg.h    |    1 +
>  drivers/gpu/drm/i915/intel_panel.c |   22 ++++++++++++++++++----
>  2 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h
> b/drivers/gpu/drm/i915/i915_reg.h
> index 5d5def7..a832028 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -3275,6 +3275,7 @@
>  #define  PWM_POLARITY_ACTIVE_HIGH2     (0 << 28)
>
>  #define BLC_PWM_PCH_CTL2       0xc8254
> +#define BLC_PWM_PCH_FREQ_SHIFT 16
>
>  #define PCH_PP_STATUS          0xc7200
>  #define PCH_PP_CONTROL         0xc7204
> diff --git a/drivers/gpu/drm/i915/intel_panel.c
> b/drivers/gpu/drm/i915/intel_panel.c
> index 05f500c..8205945 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -161,6 +161,12 @@ static u32 i915_read_blc_pwm_ctl(struct
> drm_i915_private *dev_priv)
>        return val;
>  }
>
> +static u32 intel_panel_get_default_backlight_period(struct drm_device
> *dev)
> +{
> +       /* The default number of clock cycles in one backlight PWM period.
> */
> +       return 0x1000;
> +}
> +
>  u32 intel_panel_get_max_backlight(struct drm_device *dev)
>  {
>        struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -168,11 +174,19 @@ u32 intel_panel_get_max_backlight(struct drm_device
> *dev)
>
>        max = i915_read_blc_pwm_ctl(dev_priv);
>        if (max == 0) {
> -               /* XXX add code here to query mode clock or hardware clock
> -                * and program max PWM appropriately.
> +               /* If no max backlight was found, use the default PWM
> period as
> +                * the max backlight value.
>                 */
> -               printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
> -               return 1;
> +               max = intel_panel_get_default_backlight_period(dev);
> +               if (HAS_PCH_SPLIT(dev_priv->dev)) {
> +                       u32 val = max << BLC_PWM_PCH_FREQ_SHIFT;
> +                       I915_WRITE(BLC_PWM_PCH_CTL2, val);
> +               } else {
> +                       u32 val = max << BACKLIGHT_MODULATION_FREQ_SHIFT;
> +                       I915_WRITE(BLC_PWM_CTL, val);
> +               }
> +
> +               return max;
>        }
>
>        if (HAS_PCH_SPLIT(dev)) {
> --
> 1.7.2.3
>
>

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Re: [PATCH] drivers: i915: Default max backlight brightness value

[Simon Que]

On Fri, Oct 14, 2011 at 4:46 PM, Simon Que <sque@chromium.org> wrote:
> In the native backlight driver, use 4096 (0x1000) as the default backlight
> period, and use the period as the default max brightness.
>
> The default brightness is defined in a separate function that can be
> expanded to allow for different defaults on different systems in the
> future.
>
> Change-Id: Ie783b53dd034dcd7bf42e24ffc911cf2f10a5676
> Signed-off-by: Simon Que <sque@chromium.org>
> ---
>  drivers/gpu/drm/i915/i915_reg.h    |    1 +
>  drivers/gpu/drm/i915/intel_panel.c |   22 ++++++++++++++++++----
>  2 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 5d5def7..a832028 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -3275,6 +3275,7 @@
>  #define  PWM_POLARITY_ACTIVE_HIGH2     (0 << 28)
>
>  #define BLC_PWM_PCH_CTL2       0xc8254
> +#define BLC_PWM_PCH_FREQ_SHIFT 16
>
>  #define PCH_PP_STATUS          0xc7200
>  #define PCH_PP_CONTROL         0xc7204
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index 05f500c..8205945 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -161,6 +161,12 @@ static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
>        return val;
>  }
>
> +static u32 intel_panel_get_default_backlight_period(struct drm_device *dev)
> +{
> +       /* The default number of clock cycles in one backlight PWM period. */
> +       return 0x1000;
> +}
> +
>  u32 intel_panel_get_max_backlight(struct drm_device *dev)
>  {
>        struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -168,11 +174,19 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
>
>        max = i915_read_blc_pwm_ctl(dev_priv);
>        if (max == 0) {
> -               /* XXX add code here to query mode clock or hardware clock
> -                * and program max PWM appropriately.
> +               /* If no max backlight was found, use the default PWM period as
> +                * the max backlight value.
>                 */
> -               printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
> -               return 1;
> +               max = intel_panel_get_default_backlight_period(dev);
> +               if (HAS_PCH_SPLIT(dev_priv->dev)) {
> +                       u32 val = max << BLC_PWM_PCH_FREQ_SHIFT;
> +                       I915_WRITE(BLC_PWM_PCH_CTL2, val);
> +               } else {
> +                       u32 val = max << BACKLIGHT_MODULATION_FREQ_SHIFT;
> +                       I915_WRITE(BLC_PWM_CTL, val);
> +               }
> +
> +               return max;
>        }
>
>        if (HAS_PCH_SPLIT(dev)) {
> --
> 1.7.2.3
>
>

Please provide feedback on this patch.  I am hoping that more people
are available now that the Linux Conference is over. :)

Re: [PATCH] drivers: i915: Default max backlight brightness value

[Matthew Garrett]

On Fri, Oct 14, 2011 at 04:46:57PM -0700, Simon Que wrote:

Sorry, I thought I'd replied to this already. Sorry about that.

> +static u32 intel_panel_get_default_backlight_period(struct drm_device *dev)
> +{
> +	/* The default number of clock cycles in one backlight PWM period. */
> +	return 0x1000;

I'm uncomfortable with just hardcoding this, especially given that the 
comment you're removing implies that it's possible to infer the correct 
value from other GPU values. If this does vary between machines then 
simply hardcoding it now isn't really any better than the existing error 
path - it might make things better for some systems, but it has the 
potential to break hardware that expects a different value and no longer 
generates an error in that case.

-- 
Matthew Garrett | mjg59@srcf.ucam.org