drm/nouveau/gpio: fail if gpu external power is missing

Currently, nouveau doesn't check if GPU is missing power. This
patch makes nouveau fail when this happens on latest GPUs.

It checks GPIO function 121 (External Power Emergency), which
should detect power problems on GPU initialization.

This can be disabled with nouveau.config=NvPowerChecks=1

Tested on TU104, GP106 and GF100.

v3:
*  Add config override for disabling power checks
Signed-off-by: Mark Menzynski <mmenzyns@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/subdev/bios/gpio.h

@@ -7,6 +7,7 @@ enum dcb_gpio_func_name {
 	DCB_GPIO_TVDAC0 = 0x0c,
 	DCB_GPIO_TVDAC1 = 0x2d,
 	DCB_GPIO_FAN_SENSE = 0x3d,
+	DCB_GPIO_EXT_POWER_LOW = 0x79,
 	DCB_GPIO_LOGO_LED_PWM = 0x84,
 	DCB_GPIO_UNUSED = 0xff,
 	DCB_GPIO_VID0 = 0x04,

drivers/gpu/drm/nouveau/nvkm/subdev/gpio/base.c

@@ -23,6 +23,7 @@
  */
 #include "priv.h"
 
+#include <core/option.h>
 #include <core/notify.h>
 
 static int
@@ -182,12 +183,41 @@ static const struct dmi_system_id gpio_reset_ids[] = {
 	{ }
 };
 
+static enum dcb_gpio_func_name power_checks[] = {
+	DCB_GPIO_EXT_POWER_LOW,
+};
+
 static int
 nvkm_gpio_init(struct nvkm_subdev *subdev)
 {
 	struct nvkm_gpio *gpio = nvkm_gpio(subdev);
+	struct dcb_gpio_func func;
+	int ret;
+	int i;
+
 	if (dmi_check_system(gpio_reset_ids))
 		nvkm_gpio_reset(gpio, DCB_GPIO_UNUSED);
+
+	if (nvkm_boolopt(subdev->device->cfgopt, "NvPowerChecks", true)) {
+		for (i = 0; i < ARRAY_SIZE(power_checks); ++i) {
+			ret = nvkm_gpio_find(gpio, 0, power_checks[i],
+					     DCB_GPIO_UNUSED, &func);
+			if (ret)
+				continue;
+
+			ret = nvkm_gpio_get(gpio, 0, func.func, func.line);
+			if (!ret)
+				continue;
+
+			nvkm_error(&gpio->subdev,
+				   "GPU is missing power, check its power "
+				   "cables.  Boot with "
+				   "nouveau.config=NvPowerChecks=0 to "
+				   "disable.\n");
+			return -EINVAL;
+		}
+	}
+
 	return 0;
 }