nb/intel/gm45: Set display backlight according to EDID string

Add some known good values for some thinkpads displays.

Known good means that at this pwm frequency the display is evenly lit
on all duty cycles, the display makes minimal to no noise at lower
duty cycles and the display does not flicker. This values differs from
vendor (which uses an obviously wrong display clock  (190MHz instead
of 320MHz) resulting in frequency more than 60% off the intended
value.

TESTED on Thinkpad X200 with edid ascii string in list and removed
from list to see if notice message is shown.

Change-Id: Id7bc0d453fac31e806852206ba2c895720b2c843
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19500
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

3 files changed, 41 insertions, 6 deletions

diff --git a/src/northbridge/intel/gm45/chip.h b/src/northbridge/intel/gm45/chip.h
index a281ee96d9..150dd9b33d 100644
--- a/src/northbridge/intel/gm45/chip.h
+++ b/src/northbridge/intel/gm45/chip.h
@@ -26,7 +26,7 @@ struct northbridge_intel_gm45_config {
 	u16 gpu_panel_power_backlight_off_delay; /* Tx time sequence */
 	u8 gpu_panel_power_cycle_delay;          /* T4 time sequence */
 	struct i915_gpu_controller_info gfx;
-	u16 pwm_freq;
+	u16 default_pwm_freq;
 	u8 duty_cycle;
 
 	/*
diff --git a/src/northbridge/intel/gm45/gm45.h b/src/northbridge/intel/gm45/gm45.h
index 258809fe8a..34f734c5cb 100644
--- a/src/northbridge/intel/gm45/gm45.h
+++ b/src/northbridge/intel/gm45/gm45.h
@@ -436,6 +436,13 @@ u32 decode_igd_gtt_size(u32 gsm);
 
 void init_iommu(void);
 
+struct blc_pwm_t {
+	char ascii_string[13];
+	int pwm_freq; /* In Hz */
+};
+int get_blc_values(const struct blc_pwm_t **entries);
+
+
 #if ENV_RAMSTAGE && !defined(__SIMPLE_DEVICE__)
 #include <device/device.h>
 
diff --git a/src/northbridge/intel/gm45/gma.c b/src/northbridge/intel/gm45/gma.c
index 6ba43a26c0..c060bb0be7 100644
--- a/src/northbridge/intel/gm45/gma.c
+++ b/src/northbridge/intel/gm45/gma.c
@@ -653,12 +653,16 @@ static u32 freq_to_blc_pwm_ctl(struct device *const dev,
 		return (blc_mod << 16) | blc_mod;
 }
 
-static void gma_pm_init_post_vbios(struct device *const dev)
+static void gma_pm_init_post_vbios(struct device *const dev,
+				const char *edid_ascii_string)
 {
 	const struct northbridge_intel_gm45_config *const conf = dev->chip_info;
 
 	u32 reg32;
 	u8 reg8;
+	const struct blc_pwm_t *blc_pwm;
+	int blc_array_len, i;
+	u16 pwm_freq = 0;
 
 	/* Setup Panel Power On Delays */
 	reg32 = gtt_read(PP_ON_DELAYS);
@@ -689,11 +693,35 @@ static void gma_pm_init_post_vbios(struct device *const dev)
 	reg8 = 100;
 	if (conf->duty_cycle != 0)
 		reg8 = conf->duty_cycle;
-	if (conf->pwm_freq == 0)
+	blc_array_len = get_blc_values(&blc_pwm);
+	if (conf->default_pwm_freq != 0)
+		pwm_freq = conf->default_pwm_freq;
+
+	/* Find EDID string and pwm freq in lookup table */
+	for (i = 0; i < blc_array_len; i++) {
+		if (!strncmp(blc_pwm[i].ascii_string, edid_ascii_string,
+				strlen(blc_pwm[i].ascii_string))) {
+			pwm_freq = blc_pwm[i].pwm_freq;
+			printk(BIOS_DEBUG, "Found EDID string: %s in lookup table, pwm: %dHz\n",
+				blc_pwm[i].ascii_string, pwm_freq);
+			break;
+		}
+	}
+
+	if (i == blc_array_len)
+		printk(BIOS_NOTICE, "Your panels EDID `%s` wasn't found in the"
+			"lookup table.\n You may have issues with your panels"
+			"backlight.\n If you want to help improving coreboot"
+			"please report: this EDID string\n and the result"
+			"of `intel_read read BLC_PWM_CTL`"
+			"(from intel-gpu-tools)\n while running vendor BIOS\n",
+			edid_ascii_string);
+
+	if (pwm_freq == 0)
 		gtt_write(BLC_PWM_CTL, 0x06100610);
 	else
-		gtt_write(BLC_PWM_CTL, freq_to_blc_pwm_ctl(dev,
-						conf->pwm_freq,	reg8));
+		gtt_write(BLC_PWM_CTL, freq_to_blc_pwm_ctl(dev, pwm_freq,
+								reg8));
 }
 
 static void gma_func0_init(struct device *dev)
@@ -726,7 +754,7 @@ static void gma_func0_init(struct device *dev)
 	decode_edid(edid_data_lvds, sizeof(edid_data_lvds), &edid_lvds);
 
 	/* Post VBIOS init */
-	gma_pm_init_post_vbios(dev);
+	gma_pm_init_post_vbios(dev, edid_lvds.ascii_string);
 
 	if (IS_ENABLED(CONFIG_MAINBOARD_DO_NATIVE_VGA_INIT))
 		gma_ngi(dev, &edid_lvds);