drm/simpledrm: Add support for multiple "power-domains"

Multiple power domains need to be handled explicitly in each driver. The
driver core can not handle it automatically since it is not aware of
power sequencing requirements the hardware might have. This is not a
problem for simpledrm since everything is expected to be powered on by
the bootloader. simpledrm has just ensure it remains powered on during
its lifetime.
This is required on Apple silicon M2 and M2 Pro/Max/Ultra desktop
systems. The HDMI output initialized by the bootloader requires keeping
the display controller and a DP phy power domain on.
Signed-off-by: Janne Grunau <j@jannau.net>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230912-simpledrm-multiple-power-domains-v2-1-01b66bfb1980@jannau.net

drivers/gpu/drm/tiny/simpledrm.c

@@ -6,6 +6,7 @@
 #include <linux/of_address.h>
 #include <linux/platform_data/simplefb.h>
 #include <linux/platform_device.h>
+#include <linux/pm_domain.h>
 #include <linux/regulator/consumer.h>
 
 #include <drm/drm_aperture.h>
@@ -227,6 +228,12 @@ struct simpledrm_device {
 	unsigned int regulator_count;
 	struct regulator **regulators;
 #endif
+	/* power-domains */
+#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
+	int pwr_dom_count;
+	struct device **pwr_dom_devs;
+	struct device_link **pwr_dom_links;
+#endif
 
 	/* simplefb settings */
 	struct drm_display_mode mode;
@@ -468,6 +475,101 @@ static int simpledrm_device_init_regulators(struct simpledrm_device *sdev)
 }
 #endif
 
+#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
+/*
+ * Generic power domain handling code.
+ *
+ * Here we handle the power-domains properties of our "simple-framebuffer"
+ * dt node. This is only necessary if there is more than one power-domain.
+ * A single power-domains is handled automatically by the driver core. Multiple
+ * power-domains have to be handled by drivers since the driver core can't know
+ * the correct power sequencing. Power sequencing is not an issue for simpledrm
+ * since the bootloader has put the power domains already in the correct state.
+ * simpledrm has only to ensure they remain active for its lifetime.
+ *
+ * When the driver unloads, we detach from the power-domains.
+ *
+ * We only complain about errors here, no action is taken as the most likely
+ * error can only happen due to a mismatch between the bootloader which set
+ * up the "simple-framebuffer" dt node, and the PM domain providers in the
+ * device tree. Chances are that there are no adverse effects, and if there are,
+ * a clean teardown of the fb probe will not help us much either. So just
+ * complain and carry on, and hope that the user actually gets a working fb at
+ * the end of things.
+ */
+static void simpledrm_device_detach_genpd(void *res)
+{
+	int i;
+	struct simpledrm_device *sdev = res;
+
+	if (sdev->pwr_dom_count <= 1)
+		return;
+
+	for (i = sdev->pwr_dom_count - 1; i >= 0; i--) {
+		if (!sdev->pwr_dom_links[i])
+			device_link_del(sdev->pwr_dom_links[i]);
+		if (!IS_ERR_OR_NULL(sdev->pwr_dom_devs[i]))
+			dev_pm_domain_detach(sdev->pwr_dom_devs[i], true);
+	}
+}
+
+static int simpledrm_device_attach_genpd(struct simpledrm_device *sdev)
+{
+	struct device *dev = sdev->dev.dev;
+	int i;
+
+	sdev->pwr_dom_count = of_count_phandle_with_args(dev->of_node, "power-domains",
+							 "#power-domain-cells");
+	/*
+	 * Single power-domain devices are handled by driver core nothing to do
+	 * here. The same for device nodes without "power-domains" property.
+	 */
+	if (sdev->pwr_dom_count <= 1)
+		return 0;
+
+	sdev->pwr_dom_devs = devm_kcalloc(dev, sdev->pwr_dom_count,
+					       sizeof(*sdev->pwr_dom_devs),
+					       GFP_KERNEL);
+	if (!sdev->pwr_dom_devs)
+		return -ENOMEM;
+
+	sdev->pwr_dom_links = devm_kcalloc(dev, sdev->pwr_dom_count,
+						sizeof(*sdev->pwr_dom_links),
+						GFP_KERNEL);
+	if (!sdev->pwr_dom_links)
+		return -ENOMEM;
+
+	for (i = 0; i < sdev->pwr_dom_count; i++) {
+		sdev->pwr_dom_devs[i] = dev_pm_domain_attach_by_id(dev, i);
+		if (IS_ERR(sdev->pwr_dom_devs[i])) {
+			int ret = PTR_ERR(sdev->pwr_dom_devs[i]);
+			if (ret == -EPROBE_DEFER) {
+				simpledrm_device_detach_genpd(sdev);
+				return ret;
+			}
+			drm_warn(&sdev->dev,
+				 "pm_domain_attach_by_id(%u) failed: %d\n", i, ret);
+			continue;
+		}
+
+		sdev->pwr_dom_links[i] = device_link_add(dev,
+							 sdev->pwr_dom_devs[i],
+							 DL_FLAG_STATELESS |
+							 DL_FLAG_PM_RUNTIME |
+							 DL_FLAG_RPM_ACTIVE);
+		if (!sdev->pwr_dom_links[i])
+			drm_warn(&sdev->dev, "failed to link power-domain %d\n", i);
+	}
+
+	return devm_add_action_or_reset(dev, simpledrm_device_detach_genpd, sdev);
+}
+#else
+static int simpledrm_device_attach_genpd(struct simpledrm_device *sdev)
+{
+	return 0;
+}
+#endif
+
 /*
  * Modesetting
  */
@@ -651,6 +753,9 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 	if (ret)
 		return ERR_PTR(ret);
 	ret = simpledrm_device_init_regulators(sdev);
+	if (ret)
+		return ERR_PTR(ret);
+	ret = simpledrm_device_attach_genpd(sdev);
 	if (ret)
 		return ERR_PTR(ret);