drm/fb-helper: Initialize fb-helper's preferred BPP in prepare function

Initialize the fb-helper's preferred_bpp field early from within
drm_fb_helper_prepare(); instead of the later client hot-plugging
callback. This simplifies the generic fbdev setup function.

No real changes, but all drivers' fbdev code has to be adapted.

v3:
	* build with CONFIG_DRM_FBDEV_EMULATION unset (kernel test bot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125200415.14123-7-tzimmermann@suse.de

1 files changed, 18 insertions, 4 deletions

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index b1cf58fb698d..97b34f377fe8 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -414,14 +414,30 @@ static void drm_fb_helper_damage_work(struct work_struct *work)
  * drm_fb_helper_prepare - setup a drm_fb_helper structure
  * @dev: DRM device
  * @helper: driver-allocated fbdev helper structure to set up
+ * @preferred_bpp: Preferred bits per pixel for the device.
  * @funcs: pointer to structure of functions associate with this helper
  *
  * Sets up the bare minimum to make the framebuffer helper usable. This is
  * useful to implement race-free initialization of the polling helpers.
  */
 void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
+			   unsigned int preferred_bpp,
 			   const struct drm_fb_helper_funcs *funcs)
 {
+	/*
+	 * Pick a preferred bpp of 32 if no value has been given. This
+	 * will select XRGB8888 for the framebuffer formats. All drivers
+	 * have to support XRGB8888 for backwards compatibility with legacy
+	 * userspace, so it's the safe choice here.
+	 *
+	 * TODO: Replace struct drm_mode_config.preferred_depth and this
+	 *       bpp value with a preferred format that is given as struct
+	 *       drm_format_info. Then derive all other values from the
+	 *       format.
+	 */
+	if (!preferred_bpp)
+		preferred_bpp = 32;
+
 	INIT_LIST_HEAD(&helper->kernel_fb_list);
 	spin_lock_init(&helper->damage_lock);
 	INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
@@ -430,6 +446,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
 	mutex_init(&helper->lock);
 	helper->funcs = funcs;
 	helper->dev = dev;
+	helper->preferred_bpp = preferred_bpp;
 }
 EXPORT_SYMBOL(drm_fb_helper_prepare);
 
@@ -2175,7 +2192,6 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper)
 /**
  * drm_fb_helper_initial_config - setup a sane initial connector configuration
  * @fb_helper: fb_helper device struct
- * @bpp_sel: bpp value to use for the framebuffer configuration
  *
  * Scans the CRTCs and connectors and tries to put together an initial setup.
  * At the moment, this is a cloned configuration across all heads with
@@ -2213,15 +2229,13 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper)
  * RETURNS:
  * Zero if everything went ok, nonzero otherwise.
  */
-int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
+int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper)
 {
 	int ret;
 
 	if (!drm_fbdev_emulation)
 		return 0;
 
-	fb_helper->preferred_bpp = bpp_sel;
-
 	mutex_lock(&fb_helper->lock);
 	ret = __drm_fb_helper_initial_config_and_unlock(fb_helper);