drm/i915/bdb: Fix version check

With patch "drm/i915/vbt: Fix backlight parsing for VBT 234+"
the size of bdb_lfp_backlight_data structure has been increased,
causing if-statement in the parse_lfp_backlight function
that comapres this structure size to the one retrieved from BDB,
always to fail for older revisions.
This patch calculates expected size of the structure for a given
BDB version and compares it with the value gathered from BDB.
Tested on Chromebook Pixelbook (Nocturne) (reports bdb->version = 221)

Fixes: d381baad29b4 ("drm/i915/vbt: Fix backlight parsing for VBT 234+")

Tested-by: Lukasz Majczak <lma@semihalf.com>
Signed-off-by: Lukasz Majczak <lma@semihalf.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210930134606.227234-1-lma@semihalf.com

diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 3c25926..f9776ca 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -451,13 +451,23 @@ parse_lfp_backlight(struct drm_i915_private *i915,
        }
 
        i915->vbt.backlight.type = INTEL_BACKLIGHT_DISPLAY_DDI;
-       if (bdb->version >= 191 &&
-           get_blocksize(backlight_data) >= sizeof(*backlight_data)) {
-               const struct lfp_backlight_control_method *method;
+       if (bdb->version >= 191) {
+               size_t exp_size;
 
-               method = &backlight_data->backlight_control[panel_type];
-               i915->vbt.backlight.type = method->type;
-               i915->vbt.backlight.controller = method->controller;
+               if (bdb->version >= 236)
+                       exp_size = sizeof(struct bdb_lfp_backlight_data);
+               else if (bdb->version >= 234)
+                       exp_size = EXP_BDB_LFP_BL_DATA_SIZE_REV_234;
+               else
+                       exp_size = EXP_BDB_LFP_BL_DATA_SIZE_REV_191;
+
+               if (get_blocksize(backlight_data) >= exp_size) {
+                       const struct lfp_backlight_control_method *method;
+
+                       method = &backlight_data->backlight_control[panel_type];
+                       i915->vbt.backlight.type = method->type;
+                       i915->vbt.backlight.controller = method->controller;
+               }
        }
 
        i915->vbt.backlight.pwm_freq_hz = entry->pwm_freq_hz;

diff --git a/drivers/gpu/drm/i915/display/intel_vbt_defs.h b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
index 330077c..a2108a8 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_vbt_defs.h
+++ b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
@@ -814,6 +814,11 @@ struct lfp_brightness_level {
        u16 reserved;
 } __packed;
 
+#define EXP_BDB_LFP_BL_DATA_SIZE_REV_191 \
+       offsetof(struct bdb_lfp_backlight_data, brightness_level)
+#define EXP_BDB_LFP_BL_DATA_SIZE_REV_234 \
+       offsetof(struct bdb_lfp_backlight_data, brightness_precision_bits)
+
 struct bdb_lfp_backlight_data {
        u8 entry_size;
        struct lfp_backlight_data_entry data[16];