[Intel-gfx] [PATCH v2] drivers: i915: Default backlight PWM frequency
Olof Johansson
olof at lixom.net
Fri Nov 11 22:19:31 CET 2011
Hi,
A collection of nits below.
Thanks,
-Olof
On Thu, Nov 10, 2011 at 07:48:55PM -0800, Simon Que wrote:
> If the firmware did not initialize the backlight PWM registers, set up a
> default PWM frequency of 200 Hz. This is determined using the following
> formula:
>
> freq = refclk / (128 * pwm_max)
>
> The PWM register allows the max PWM value to be set. So we want to use
> the formula, where freq = 200:
>
> pwm_max = refclk / (128 * freq)
>
> This patch will, in the case of missing PWM register initialization
> values, look for the reference clock frequency. Based on that, it sets
> an appropriate max PWM value for a frequency of 200 Hz.
>
> If no refclk frequency is found, the max PWM will be zero, which results
> in no change to the PWM registers.
>
> Signed-off-by: Simon Que <sque at chromium.org>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 1 +
> drivers/gpu/drm/i915/intel_panel.c | 37 +++++++++++++++++++++++++++++------
> 2 files changed, 31 insertions(+), 7 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 f15388c..f865e52 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -32,6 +32,10 @@
>
> #define PCI_LBPC 0xf4 /* legacy/combination backlight modes */
>
> +/* For computing default PWM settings */
> +#define DEFAULT_BACKLIGHT_PWM_FREQ 200
> +#define BACKLIGHT_REFCLK_DIVISOR 128
I would a bit more comment above. Maybe something like:
/* These are used to calculate a reasonable default when firmware has not
* configured a maximum PWM frequency, with 200Hz as current target.
*/
> +
> void
> intel_fixed_panel_mode(struct drm_display_mode *fixed_mode,
> struct drm_display_mode *adjusted_mode)
> @@ -129,12 +133,31 @@ static int is_backlight_combination_mode(struct drm_device *dev)
> return 0;
> }
>
> +static u32 i915_get_default_max_backlight(struct drm_i915_private *dev_priv)
Having a 'get' function that has side effects is misleading.
'i915_set_default_max_backlight' is a better name (and not returning the new
max).
> +{
> + u32 refclk_freq_mhz = 0;
> + u32 max_pwm = 0;
No need to set max_pwm to 0.
Empty line between variables and code.
> + if (HAS_PCH_SPLIT(dev_priv->dev))
> + refclk_freq_mhz = I915_READ(PCH_RAWCLK_FREQ) & RAWCLK_FREQ_MASK;
> + else if (dev_priv->lvds_use_ssc)
> + refclk_freq_mhz = dev_priv->lvds_ssc_freq;
> +
> + max_pwm = refclk_freq_mhz * 1000000 /
> + (BACKLIGHT_REFCLK_DIVISOR * DEFAULT_BACKLIGHT_PWM_FREQ);
> +
> + if (HAS_PCH_SPLIT(dev_priv->dev))
> + dev_priv->saveBLC_PWM_CTL2 = max_pwm << BLC_PWM_PCH_FREQ_SHIFT;
> + else
> + dev_priv->saveBLC_PWM_CTL = max_pwm <<
> + BACKLIGHT_MODULATION_FREQ_SHIFT;
> + return max_pwm;
> +}
> +
> static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
> {
> u32 val;
>
> - /* Restore the CTL value if it lost, e.g. GPU reset */
> -
> + /* Restore the CTL value if it was lost, e.g. GPU reset */
> if (HAS_PCH_SPLIT(dev_priv->dev)) {
> val = I915_READ(BLC_PWM_PCH_CTL2);
> if (dev_priv->saveBLC_PWM_CTL2 == 0) {
> @@ -168,11 +191,11 @@ 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.
> - */
> - printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
> - return 1;
> + /* If backlight PWM registers have not been set, set them to */
> + /* default backlight PWM settings. */
/* Kernel multi-line comment style
* is like this.
*/
> + max = i915_get_default_max_backlight(dev_priv);
> + i915_read_blc_pwm_ctl(dev_priv);
max = i915_read_..
> + return max;
If you return here you won't be doing the same math as below, that looks like
a bug.
> }
>
> if (HAS_PCH_SPLIT(dev)) {
-Olof
More information about the Intel-gfx
mailing list