soc/intel/skl/graphics: Implement panel setup

Logs from Linux' i915 suggest that not even the FSP/GOP takes proper
care of this. The sequence is mostly the same as on older platforms,
with a slightly different configuration of the backlight PWM.

We light the panel up with 50% PWM duty cycle. This often results in
an already rather high perceived brightness, but shouldn't be too
blinding.

Change-Id: I762a77c8df023a4c14af502af5edfeeb961da1ae
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/30246
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/soc/intel/skylake/chip.h

@@ -48,6 +48,18 @@ struct soc_intel_skylake_config {
 	/* Common struct containing soc config data required by common code */
 	struct soc_intel_common_config common_soc_config;
 
+	/* IGD panel configuration */
+	unsigned int gpu_pp_up_delay_ms;
+	unsigned int gpu_pp_down_delay_ms;
+	unsigned int gpu_pp_cycle_delay_ms;
+	unsigned int gpu_pp_backlight_on_delay_ms;
+	unsigned int gpu_pp_backlight_off_delay_ms;
+	unsigned int gpu_pch_backlight_pwm_hz;
+	enum {
+		GPU_BACKLIGHT_POLARITY_HIGH = 0,
+		GPU_BACKLIGHT_POLARITY_LOW,
+	} gpu_pch_backlight_polarity;
+
 	/*
 	 * Interrupt Routing configuration
 	 * If bit7 is 1, the interrupt is disabled.

src/soc/intel/skylake/graphics.c

@@ -16,9 +16,11 @@
 
 #include <bootmode.h>
 #include <cbmem.h>
+#include <commonlib/helpers.h>
 #include <console/console.h>
 #include <device/pci.h>
 #include <device/pci_ops.h>
+#include <device/resource.h>
 #include <drivers/intel/gma/i915_reg.h>
 #include <drivers/intel/gma/libgfxinit.h>
 #include <intelblocks/graphics.h>
@@ -32,10 +34,72 @@ uintptr_t fsp_soc_get_igd_bar(void)
 	return graphics_get_memory_base();
 }
 
+static void graphics_setup_panel(struct device *dev)
+{
+	struct soc_intel_skylake_config *conf = dev->chip_info;
+	struct resource *mmio_res;
+	uint8_t *base;
+	u32 reg32;
+
+	if (!conf)
+		return;
+
+	mmio_res = find_resource(dev, PCI_BASE_ADDRESS_0);
+	if (!mmio_res || !mmio_res->base)
+		return;
+	base = (void *)(uintptr_t)mmio_res->base;
+
+	reg32 = conf->gpu_pp_up_delay_ms * 10 << 16;
+	reg32 |= conf->gpu_pp_backlight_on_delay_ms * 10;
+	write32(base + PCH_PP_ON_DELAYS, reg32);
+
+	reg32 = conf->gpu_pp_down_delay_ms * 10 << 16;
+	reg32 |= conf->gpu_pp_backlight_off_delay_ms * 10;
+	write32(base + PCH_PP_OFF_DELAYS, reg32);
+
+	reg32 = read32(base + PCH_PP_DIVISOR);
+	reg32 &= ~0x1f;
+	reg32 |= (DIV_ROUND_UP(conf->gpu_pp_cycle_delay_ms, 100) + 1) & 0x1f;
+	write32(base + PCH_PP_DIVISOR, reg32);
+
+	/* So far all devices seem to use the PCH PWM function.
+	   The CPU PWM registers are all zero after reset.      */
+	if (conf->gpu_pch_backlight_pwm_hz) {
+		/* Reference clock is 24MHz. We can choose either a 16
+		   or a 128 step increment. Use 16 if we would have less
+		   than 100 steps otherwise. */
+		const unsigned int hz_limit = 24 * 1000 * 1000 / 128 / 100;
+		unsigned int pwm_increment, pwm_period;
+		u32 south_chicken1;
+
+		south_chicken1 = read32(base + SOUTH_CHICKEN1);
+		if (conf->gpu_pch_backlight_pwm_hz > hz_limit) {
+			pwm_increment = 16;
+			south_chicken1 &= ~1;
+		} else {
+			pwm_increment = 128;
+			south_chicken1 |= 1;
+		}
+		write32(base + SOUTH_CHICKEN1, south_chicken1);
+
+		pwm_period = 24 * 1000 * 1000 / pwm_increment
+				/ conf->gpu_pch_backlight_pwm_hz;
+		/* Start with a 50% duty cycle. */
+		write32(base + BLC_PWM_PCH_CTL2,
+			pwm_period << 16 | pwm_period / 2);
+
+		write32(base + BLC_PWM_PCH_CTL1,
+			!!conf->gpu_pch_backlight_polarity << 29 |
+			BLM_PCH_PWM_ENABLE);
+	}
+}
+
 void graphics_soc_init(struct device *dev)
 {
 	u32 ddi_buf_ctl;
 
+	graphics_setup_panel(dev);
+
 	/*
 	 * Enable DDI-A (eDP) 4-lane operation if the link is not up yet.
 	 * This will allow the kernel to use 4-lane eDP links properly