[display] Flush cached brightness when adjustment fails. Fixes JB#47229

In devices which use kms/drm (such as Sony Xperia 10) all adjustment
attempts made while display is not ready get ignored and brightness
gets reset on compositor change. The mce side brightness value caching
is not prepared to handle this kind of situation, which easily leads
to display staying dimmer than expected due to cached value getting
out of sync with reality.

Flush cached brightness value on adjustment failures.

Update cached brightness value only after successful adjustments.

Add helper functions for performing common tasks.

As the logic still makes adjustment attempts in situations where they
are not going to be accepted by drm drivers, tweak logging to reduce
noise from  adjustment failures a bit.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

modules/display.c

@@ -472,10 +472,12 @@ static void                mdy_hbm_rethink(void);
  * ------------------------------------------------------------------------- */
 
 #ifdef ENABLE_HYBRIS
-static void                mdy_brightness_set_level_hybris(int number);
+static bool                mdy_brightness_set_level_hybris(int number);
 #endif
-static void                mdy_brightness_set_level_default(int number);
+static bool                mdy_brightness_set_level_default(int number);
+static int                 mdy_brightness_normalize_level(int number);
 static void                mdy_brightness_set_level(int number);
+static void                mdy_brightness_forget_level(void);
 
 static void                mdy_brightness_fade_continue_with_als(fader_type_t fader_type);
 static void                mdy_brightness_force_level(int number);
@@ -2625,7 +2627,7 @@ static output_state_t mdy_brightness_level_output =
  *
  * @param number brightness value; after bounds checking
  */
-static void (*mdy_brightness_set_level_hook)(int number) = mdy_brightness_set_level_default;
+static bool (*mdy_brightness_set_level_hook)(int number) = mdy_brightness_set_level_default;
 
 /** Is hardware driven display fading supported */
 static gboolean mdy_brightness_hw_fading_is_supported = FALSE;
@@ -2705,49 +2707,67 @@ static gboolean mdy_orientation_change_is_activity = MCE_DEFAULT_ORIENTATION_CHA
 static guint    mdy_orientation_change_is_activity_setting_id = 0;
 
 /** Set display brightness via sysfs write */
-static void mdy_brightness_set_level_default(int number)
+static bool mdy_brightness_set_level_default(int number)
 {
-    mce_write_number_string_to_file(&mdy_brightness_level_output, number);
+    return mce_write_number_string_to_file(&mdy_brightness_level_output, number);
 }
 
 #ifdef ENABLE_HYBRIS
 /** Set display brightness via libhybris */
-static void mdy_brightness_set_level_hybris(int number)
+static bool mdy_brightness_set_level_hybris(int number)
 {
-    mce_hybris_backlight_set_brightness(number);
+    return mce_hybris_backlight_set_brightness(number);
 }
 #endif
 
+/** Helper for normalizing brightness to supported range
+ *
+ * @param number  brightness value
+ *
+ * @return brightness value capped to supported range
+ */
+static int mdy_brightness_normalize_level(int number)
+{
+    if( number < 0 )
+        number = 0;
+    else if (number > mdy_brightness_level_maximum )
+        number = mdy_brightness_level_maximum;
+    return number;
+}
+
 /** Helper for updating backlight brightness with bounds checking
  *
  * @param number brightness in 0 to mdy_brightness_level_maximum range
  */
 static void mdy_brightness_set_level(int number)
 {
-    int minval = 0;
-    int maxval = mdy_brightness_level_maximum;
-
     /* If we manage to get out of hw bounds values from depths
      * of pipelines and state machines we could end up with
      * black screen without easy way out -> clip to valid range */
-    if( number < minval ) {
-        mce_log(LL_ERR, "value=%d vs min=%d", number, minval);
-        number = minval;
-    }
-    else if( number > maxval ) {
-        mce_log(LL_ERR, "value=%d vs max=%d", number, maxval);
-        number = maxval;
+    int value = mdy_brightness_normalize_level(number);
+    if( value != number )
+        mce_log(LL_ERR, "level=%d -> %d", number, value);
+
+    if( mdy_brightness_level_cached != value ) {
+        if( mdy_brightness_set_level_hook(value) ) {
+            mdy_brightness_level_cached = value;
+            mce_log(LL_DEBUG, "level: %d", mdy_brightness_level_cached);
+        }
+        else if( mdy_brightness_level_cached != -1 ) {
+            mdy_brightness_level_cached = -1;
+            mce_log(LL_WARN, "level: %d", mdy_brightness_level_cached);
+        }
     }
-    else
-        mce_log(LL_DEBUG, "value=%d", number);
+}
 
-    if( mdy_brightness_level_cached != number ) {
-        mdy_brightness_level_cached = number;
-        mdy_brightness_set_level_hook(number);
+/** Helper for flushing cached backlight brightness value
+ */
+static void mdy_brightness_forget_level(void)
+{
+    if( mdy_brightness_level_cached != -1 ) {
+        mdy_brightness_level_cached = -1;
+        mce_log(LL_DEBUG, "level: %d", mdy_brightness_level_cached);
     }
-
-    // TODO: we might want to power off fb at zero brightness
-    //       and power it up at non-zero brightness???
 }
 
 /** Helper for boosting mce scheduling priority during brightness fading
@@ -3150,8 +3170,10 @@ static void mdy_brightness_set_fade_target_ex(fader_type_t type,
     }
 
     /* Set up fade start and end brightness levels */
-    mdy_brightness_fade_start_level = mdy_brightness_level_cached;
-    mdy_brightness_fade_end_level   = new_brightness;
+    mdy_brightness_fade_start_level =
+        mdy_brightness_normalize_level(mdy_brightness_level_cached);
+    mdy_brightness_fade_end_level =
+        mdy_brightness_normalize_level(new_brightness);
 
     /* If the - possibly adjusted - transition time is so short that
      * only couple of adjustments would be made, do an immediate
@@ -8152,7 +8174,7 @@ static void mdy_stm_step(void)
              */
             int brightness = mdy_brightness_level_cached;
             mce_log(LL_WARN, "forced brightness sync to: %d", brightness);
-            mdy_brightness_level_cached = -1;
+            mdy_brightness_forget_level();
             if( brightness > 0 )
                 mdy_brightness_set_level(brightness - 1);
             mdy_brightness_set_level(brightness);
@@ -8222,7 +8244,7 @@ static void mdy_stm_step(void)
                  * the display while making exit -> we need to
                  * invalidate cached backlight brightness level
                  * and possibly power up the display again */
-                mdy_brightness_level_cached = -1;
+                mdy_brightness_forget_level();
             }
             mdy_stm_trans(STM_LEAVE_POWER_ON);
             break;
@@ -8401,7 +8423,7 @@ static void mdy_stm_step(void)
 
         if( mdy_stm_compositor_availability_changed ) {
             if( !mdy_compositor_is_available() )
-                mdy_brightness_level_cached = -1;
+                mdy_brightness_forget_level();
             mdy_stm_trans(STM_LEAVE_LOGICAL_OFF);
             break;
         }