[PATCH v2 6/9] drm/fb-helper: Support deferred setup

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

FB helper code falls back to a 1024x768 mode if no outputs are connected
or don't report back any modes upon initialization. This can be annoying
because outputs that are added to FB helper later on can't be used with
FB helper if they don't support a matching mode.

The fallback is in place because VGA connectors can happen to report an
unknown connection status even when they are in fact connected.

Some drivers have custom solutions in place to defer FB helper setup
until at least one output is connected. But the logic behind these
solutions is always the same and there is nothing driver-specific about
it, so a better alterative is to fix the FB helper core and add support
for all drivers automatically.

This patch adds support for deferred FB helper setup. It checks all the
connectors for their connection status, and if all of them report to be
disconnected marks the FB helper as needing deferred setup. Whet setup
is deferred, the FB helper core will automatically retry setup after a
hotplug event, and it will keep trying until it succeeds.

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 36 ++++++++++++++++++++++++++++++++++++
 include/drm/drm_fb_helper.h     | 21 +++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index f7722bcb0064..0911b10c711c 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -487,6 +487,9 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
 	if (!drm_fbdev_emulation)
 		return -ENODEV;
 
+	if (fb_helper->deferred_setup)
+		return 0;
+
 	mutex_lock(&fb_helper->lock);
 	drm_modeset_lock_all(dev);
 
@@ -1452,6 +1455,23 @@ unlock:
 }
 EXPORT_SYMBOL(drm_fb_helper_pan_display);
 
+static bool drm_fb_helper_maybe_connected(struct drm_fb_helper *helper)
+{
+	bool connected = false;
+	unsigned int i;
+
+	for (i = 0; i < helper->connector_count; i++) {
+		struct drm_fb_helper_connector *fb = helper->connector_info[i];
+
+		if (fb->connector->status != connector_status_disconnected) {
+			connected = true;
+			break;
+		}
+	}
+
+	return connected;
+}
+
 /*
  * Allocates the backing storage and sets up the fbdev info structure through
  * the ->fb_probe callback and then registers the fbdev and sets up the panic
@@ -1554,6 +1574,17 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 			sizes.fb_height = min_t(u32, desired_mode->vdisplay + y, sizes.fb_height);
 	}
 
+	/*
+	 * If everything's disconnected, there's no use in attempting to set
+	 * up fbdev.
+	 */
+	if (!drm_fb_helper_maybe_connected(fb_helper)) {
+		DRM_INFO("No outputs connected, deferring setup\n");
+		fb_helper->preferred_bpp = preferred_bpp;
+		fb_helper->deferred_setup = true;
+		return 0;
+	}
+
 	if (crtc_count == 0 || sizes.fb_width == -1 || sizes.fb_height == -1) {
 		/* hmm everyone went away - assume VGA cable just fell out
 		   and will come back later. */
@@ -1593,6 +1624,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 
 	list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
 
+	fb_helper->deferred_setup = false;
 	return 0;
 }
 
@@ -2294,6 +2326,10 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 	if (!drm_fbdev_emulation)
 		return 0;
 
+	if (fb_helper->deferred_setup)
+		return drm_fb_helper_initial_config(fb_helper,
+						    fb_helper->preferred_bpp);
+
 	mutex_lock(&fb_helper->lock);
 	mutex_lock(&fb_helper->dev->mode_config.mutex);
 
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 7739be08ebca..dac155ad33f6 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -219,6 +219,27 @@ struct drm_fb_helper {
 	bool delayed_hotplug;
 
 	/**
+	 * @deferred_setup:
+	 *
+	 * If no outputs are connected (disconnected or unknown) the FB helper
+	 * code will defer setup until at least one of the outputs shows up.
+	 * This field keeps track of the status so that setup can be retried
+	 * at every hotplug event until it succeeds eventually.
+	 */
+	bool deferred_setup;
+
+	/**
+	 * @preferred_bpp:
+	 *
+	 * Temporary storage for the driver's preferred BPP setting passed to
+	 * FB helper initialization. This needs to be tracked so that deferred
+	 * FB helper setup can pass this on.
+	 *
+	 * See also: @deferred_setup
+	 */
+	int preferred_bpp;
+
+	/**
 	 * @atomic:
 	 *
 	 * Use atomic updates for restore_fbdev_mode(), etc.  This defaults to
-- 
2.8.3