[Intel-gfx] [PATCH v6] drm/i915: respect the VBT minimum backlight brightness again
Stéphane ANCELOT
sancelot at free.fr
Thu Nov 12 00:40:03 PST 2015
On 12/11/2015 09:28, Shih-Yuan Lee (FourDollars) wrote:
> I think the first step is to identify which backlight interface is
> able to actually change the brightness.
> Usually there are two backlight interfaces under
> /sys/class/backlight/, i.e. /sys/class/backlight/acpi_video0 and
> /sys/class/backlight/intel_backlight.
> However you may see other different backlight interfaces under
> /sys/class/backlight/. It depends on what hardware you are using.
> Executing `cat max_brightness` under those folders can see the max
> brightness and then you can execute `echo $(($(cat max_brightness)/2))
> | sudo tee brightness` to adjust it to about 50% brightness.
>
only /sys/class/backlight/intel_backlight is present.
max_brightness is 937
these commands have no effect on display brightness:
echo 0 >brightness
echo 468 >brightness
echo 937 >brightness
Regards,
Steph
> On Thu, Nov 12, 2015 at 4:08 PM, Stéphane ANCELOT <sancelot at free.fr
> <mailto:sancelot at free.fr>> wrote:
>
> Hi,
> I have seen you were working on brightness. Right, but this is
> useful only if many worlwide users would be able to activate it.
> I have never been able to make it working on my intel systemes
> (core i5 - 4300u , core i3 ...)
> Very difficult to check where the problem is coming from, altough
> you have either an intel_backlight or acpi_backlight folder in the
> sys directory
> Regarding many many posts on the web, this sounds tricky and
> difficult to know why it has not worked, or simply the
> documentation is lacking ....
>
> Regards,
> S.Ancelot
>
>
> On 12/11/2015 06:43, Shih-Yuan Lee (FourDollars) wrote:
>
> There was a wonderful period after
>
> commit 6dda730e55f412a6dfb181cae6784822ba463847
> Author: Jani Nikula <jani.nikula at intel.com <http://intel.com>>
> Date: Tue Jun 24 18:27:40 2014 +0300
>
> drm/i915: respect the VBT minimum backlight brightness
>
> The backlight class 0 brightness means the PWM min and it does
> not turn
> off the backlight. After kernel 3.18, the backlight class 0
> brightness
> is used to turn off the backlight and the PWM min is missing.
>
> Because of
>
> commit e6755fb78e8f20ecadf2a4080084121336624ad9
> Author: Jani Nikula <jani.nikula at intel.com <http://intel.com>>
> Date: Tue Aug 12 17:11:42 2014 +0300
>
> drm/i915: switch off backlight for backlight class 0
> brightness
>
> Use "VBT backlight PWM modulation frequency 200 Hz, active
> high, min
> brightness 10, level 255" as an example. It means the VBT min
> is 10
> out of [0..255] and the PWM max is 937 from other place so the
> corresponding PWM min should be 37 (10 * 937 / 255).
>
> When we set backlight class 0 brightness, the backlight is
> turned off.
> Althought the PWM value is 37 when the backlight is off but it is
> useless. When we set set backlight class 1 brightness, the
> backlight is
> on but the PWM value is 38 and it doesn't match the
> corresponding PWM
> min of the VBT minimum backlight.
>
> And it has another minor issue that there are some backlight class
> brightness values are mapped to the same PWM value because the
> backlight
> class brightness range is larger than the valid PWM brightness
> range.
>
> The backlight class brightness range [0..937]
> The valid PWM brightness range [37..937]
>
> This commit makes that backlight class 1 brightness means the
> PWM min
> and backlight class max_brightness means the PWM max, and the
> ranges
> become
>
> The backlight class brightness range [0..901]
> The valid PWM brightness range [36..937]
>
> That's no backlight class brightness value mapped to the same
> PWM value.
>
> Signed-off-by: Shih-Yuan Lee (FourDollars)
> <sylee at canonical.com <mailto:sylee at canonical.com>>
> ---
> drivers/gpu/drm/i915/intel_panel.c | 26
> ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c
> b/drivers/gpu/drm/i915/intel_panel.c
> index b05c6d9..8efa199 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -1194,10 +1194,9 @@ static int
> intel_backlight_device_register(struct intel_connector *connector)
> props.type = BACKLIGHT_RAW;
> /*
> - * Note: Everything should work even if the backlight
> device max
> - * presented to the userspace is arbitrarily chosen.
> + * Expose the whole valid PWM brightness range to the
> backlight class.
> */
> - props.max_brightness = panel->backlight.max;
> + props.max_brightness = panel->backlight.max -
> panel->backlight.min;
> props.brightness = scale_hw_to_user(connector,
> panel->backlight.level,
> props.max_brightness);
> @@ -1400,7 +1399,8 @@ static u32 get_backlight_min_vbt(struct
> intel_connector *connector)
> struct drm_device *dev = connector->base.dev;
> struct drm_i915_private *dev_priv = dev->dev_private;
> struct intel_panel *panel = &connector->panel;
> - int min;
> + int vbt_min;
> + u32 pwm_min;
> WARN_ON(panel->backlight.max == 0);
> @@ -1411,14 +1411,24 @@ static u32
> get_backlight_min_vbt(struct intel_connector *connector)
> * against this by letting the minimum be at most
> (arbitrarily chosen)
> * 25% of the max.
> */
> - min = clamp_t(int,
> dev_priv->vbt.backlight.min_brightness, 0, 64);
> - if (min != dev_priv->vbt.backlight.min_brightness) {
> + vbt_min = clamp_t(int,
> dev_priv->vbt.backlight.min_brightness, 0, 64);
> + if (vbt_min != dev_priv->vbt.backlight.min_brightness) {
> DRM_DEBUG_KMS("clamping VBT min backlight
> %d/255 to %d/255\n",
> - dev_priv->vbt.backlight.min_brightness, min);
> + dev_priv->vbt.backlight.min_brightness, vbt_min);
> }
> /* vbt value is a coefficient in range [0..255] */
> - return scale(min, 0, 255, 0, panel->backlight.max);
> + pwm_min = scale(vbt_min, 0, 255, 0, panel->backlight.max);
> +
> + /*
> + * Because backlight class brightness 0 is used to
> turn off the backlight, we
> + * need to step down a little bit here to make
> backlight class brightness 1
> + * match the real PWM min.
> + */
> + if (pwm_min > 0)
> + return pwm_min - 1;
> + else
> + return 0;
> }
> static int lpt_setup_backlight(struct intel_connector
> *connector, enum pipe unused)
>
>
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