mb/google/brya/var/agah: Add GPU power sequencing

This patch adds support for power sequencing of the Nvidia GN3050 for
agah, which uses PCH GPIOs to control the 5 power rails required for
the GPU. The GPU is power sequenced on during mainboard
initialization, then it is enumerated on the PCI bus and its resources
are assigned. This GPU will be used in a sort of "hybrid graphics"
mode, therefore during finalization, since its PCI BARs are saved into
ACPI memory and the GPU is not required upon initial boot, the GPU is
power sequenced off.

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I1072be12ef58af5859e2a2d19c4a9c1adc0b0f88
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62384
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

4 files changed, 191 insertions, 2 deletions

diff --git a/src/mainboard/google/brya/variants/agah/Makefile.inc b/src/mainboard/google/brya/variants/agah/Makefile.inc
index 139345f260..3d5212f984 100644
--- a/src/mainboard/google/brya/variants/agah/Makefile.inc
+++ b/src/mainboard/google/brya/variants/agah/Makefile.inc
@@ -6,3 +6,4 @@ romstage-y += gpio.c
 romstage-y += memory.c
 
 ramstage-y += gpio.c
+ramstage-y += variant.c
diff --git a/src/mainboard/google/brya/variants/agah/gpio.c b/src/mainboard/google/brya/variants/agah/gpio.c
index 81c9724d5a..369e373808 100644
--- a/src/mainboard/google/brya/variants/agah/gpio.c
+++ b/src/mainboard/google/brya/variants/agah/gpio.c
@@ -75,8 +75,8 @@ static const struct pad_config override_gpio_table[] = {
 	/* D16 : ISH_UART0_CTS# ==> NC */
 	PAD_NC_LOCK(GPP_D16, NONE, LOCK_CONFIG),
 
-	/* E0 : SATAXPCIE0 ==> EN_PPVAR_GPU_NVVDD_X_OD */
-	PAD_CFG_GPO(GPP_E0, 0, DEEP),
+	/* E0 : SATAXPCIE0 ==> EN_PPVAR_GPU_NVVDD_X_ODL */
+	PAD_CFG_GPO(GPP_E0, 1, DEEP),
 	/* E3  : PROC_GP0 ==> NC */
 	PAD_NC(GPP_E3, NONE),
 	/* E4  : SATA_DEVSLP0 ==> PG_PPVAR_GPU_FBVDDQ_X_OD */
diff --git a/src/mainboard/google/brya/variants/agah/overridetree.cb b/src/mainboard/google/brya/variants/agah/overridetree.cb
index ad23f7b6f1..70bc09289d 100644
--- a/src/mainboard/google/brya/variants/agah/overridetree.cb
+++ b/src/mainboard/google/brya/variants/agah/overridetree.cb
@@ -58,6 +58,15 @@ chip soc/intel/alderlake
         }"
 
         device domain 0 on
+		device ref pcie4_0 on
+			# Enable CPU PCIe RP 1 using CLKREQ 0 and CLKSRC 0
+			register "cpu_pcie_rp[CPU_RP(1)]" = "{
+				.clk_req = 0,
+				.clk_src = 0,
+				.flags = PCIE_RP_LTR | PCIE_RP_AER,
+			}"
+			device pci 00.0 alias dgpu on end
+		end
 		device ref dtt on
 			chip drivers/intel/dptf
 				## sensor information
diff --git a/src/mainboard/google/brya/variants/agah/variant.c b/src/mainboard/google/brya/variants/agah/variant.c
new file mode 100644
index 0000000000..979e4e02ef
--- /dev/null
+++ b/src/mainboard/google/brya/variants/agah/variant.c
@@ -0,0 +1,179 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <acpi/acpi.h>
+#include <acpi/acpigen.h>
+#include <baseboard/variants.h>
+#include <delay.h>
+#include <gpio.h>
+#include <timer.h>
+#include <types.h>
+
+#define GPU_1V8_PWR_EN		GPP_E18
+#define GPU_1V8_PG		GPP_E20
+#define NV33_PWR_EN		GPP_A21
+#define NV33_PG			GPP_A22
+#define NVVDD_PWR_EN		GPP_E0
+#define NVVDD_PG		GPP_E16
+#define PEXVDD_PWR_EN		GPP_E10
+#define PEXVDD_PG		GPP_E17
+#define FBVDD_PWR_EN		GPP_A17
+#define FBVDD_PG		GPP_E4
+#define GPU_PERST_L		GPP_B3
+#define GPU_ALLRAILS_PG		GPP_E5
+
+#define DEFAULT_PG_TIMEOUT_US	20000
+
+#define VGAR_BYTE_OFFSET	5
+
+/* Maximum size of PCI config space to save. */
+#define GPU_CONFIG_SAVE_SPACE_BYTES	0x100
+
+static bool gpu_powered_on;
+
+struct power_rail_sequence {
+	const char *name;
+
+	/* This is the GPIO (output) connected to the VR's enable pin. */
+	gpio_t pwr_en_gpio;
+	bool pwr_en_active_low;
+
+	/* This is the GPIO (input) connected to the VR's power-good pin. */
+	gpio_t pg_gpio;
+};
+
+/* In GCOFF exit order (i.e., power-on order) */
+static const struct power_rail_sequence gpu_rails[] = {
+	{ "GPU 1.8V",		GPU_1V8_PWR_EN,	false, GPU_1V8_PG, },
+	{ "NV3_3",		NV33_PWR_EN,	false, NV33_PG, },
+	{ "NVVDD+MSVDD",	NVVDD_PWR_EN,	true,  NVVDD_PG, },
+	{ "PEXVDD",		PEXVDD_PWR_EN,	false, PEXVDD_PG, },
+	{ "FBVDD",		FBVDD_PWR_EN,	false, FBVDD_PG, },
+};
+
+enum rail_state {
+	RAIL_OFF = 0,
+	RAIL_ON = 1,
+};
+
+/* Assert the VR's enable pin, and wait until the VR's power-good is asserted. */
+static bool sequence_rail(const struct power_rail_sequence *seq, enum rail_state state)
+{
+	if (seq->pwr_en_active_low)
+		state = !state;
+
+	gpio_output(seq->pwr_en_gpio, state);
+	return wait_us(DEFAULT_PG_TIMEOUT_US, gpio_get(seq->pg_gpio) == state) > 0;
+}
+
+static void dgpu_power_sequence_off(void)
+{
+	/* Assert reset and clear power-good */
+	gpio_output(GPU_PERST_L, 0);
+	mdelay(5);
+
+	/* Inform the GPU that the power is no longer good. */
+	gpio_output(GPU_ALLRAILS_PG, 0);
+
+	for (int i = (int)ARRAY_SIZE(gpu_rails) - 1; i >= 0; i--) {
+		if (!sequence_rail(&gpu_rails[i], RAIL_OFF)) {
+			printk(BIOS_ERR, "Failed to disable %s rail, continuing!\n",
+			       gpu_rails[i].name);
+		}
+	}
+}
+
+static void dgpu_power_sequence_on(void)
+{
+	/* Assert PERST# */
+	gpio_output(GPU_PERST_L, 0);
+
+	for (size_t i = 0; i < ARRAY_SIZE(gpu_rails); i++) {
+		if (!sequence_rail(&gpu_rails[i], RAIL_ON)) {
+			printk(BIOS_ERR, "Failed to enable %s rail, sequencing back down!\n",
+			       gpu_rails[i].name);
+
+			/* If an error occurred, then perform the power-off sequence and
+			   return early to avoid setting GPU_ALLRAILS_PG and PERST_L. */
+			dgpu_power_sequence_off();
+			return;
+	       }
+	}
+
+	/* Set power-good and release PERST# */
+	gpio_output(GPU_ALLRAILS_PG, 1);
+	mdelay(1);
+	gpio_output(GPU_PERST_L, 1);
+
+	printk(BIOS_INFO, "Sequenced GPU successfully\n");
+	gpu_powered_on = true;
+}
+
+void variant_init(void)
+{
+	if (acpi_is_wakeup_s3())
+		return;
+
+	dgpu_power_sequence_on();
+}
+
+void variant_finalize(void)
+{
+	if (acpi_is_wakeup_s3() || !gpu_powered_on)
+		return;
+
+	/*
+	 * Because the dGPU is used here in a way similar to "hybrid graphics"
+	 * modes, it is powered down here. The DRIVERS_GFX_NVIDIA_SAVE_BARS
+	 * option is selected for agah, so the BARs will be saved to ACPI memory
+	 * during its finalize routine. Thus, it is powered down here, as the
+	 * proper resources have already been allocated.
+	 */
+	dgpu_power_sequence_off();
+
+	printk(BIOS_INFO, "GPU power sequenced off.\n");
+}
+
+/* Save PCI BARs to the ACPI copy of the "saved PCI config space" */
+void variant_fill_ssdt(const struct device *unused)
+{
+	if (!gpu_powered_on)
+		return;
+
+	const struct device *dgpu = DEV_PTR(dgpu);
+	acpigen_write_scope("\\_SB.PCI0.PEG0.PEGP");
+	acpigen_write_method("_INI", 0);
+	{
+		/* Local0 = VGAR */
+		acpigen_write_store();
+		acpigen_emit_namestring("VGAR");
+		acpigen_emit_byte(LOCAL0_OP);
+
+		/*
+		 * CreateDWordField(Local0, 11, BAR0)
+		 * BAR0 = bases[0]
+		 * CreateDWordField(Local0, 15, BAR1)
+		 * BAR1 = bases[1]
+		 * ...
+		 */
+		for (unsigned int idx = PCI_BASE_ADDRESS_0, i = 0; idx <= PCI_BASE_ADDRESS_5;
+		     idx += sizeof(uint32_t), ++i) {
+			char name[ACPI_NAME_BUFFER_SIZE];
+			const struct resource *res;
+
+			res = probe_resource(dgpu, idx);
+			if (!res)
+				continue;
+
+			snprintf(name, sizeof(name), "BAR%1d", i);
+			acpigen_write_create_dword_field(LOCAL0_OP, idx - VGAR_BYTE_OFFSET,
+							 name);
+			acpigen_write_store_int_to_namestr(res->base & 0xffffffff, name);
+		}
+
+		/* VGAR = Local0 */
+		acpigen_write_store_op_to_namestr(LOCAL0_OP, "VGAR");
+	}
+
+	acpigen_write_method_end();
+	acpigen_write_scope_end();
+}