drm/fb-helper: Consolidate CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM

Consolidate all handling of CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM by
making the module parameter optional in drm_fb_helper.c.

Without the config option, modules can set smem_start in struct
fb_info for internal usage, but not export if to userspace. The
address can only be exported by enabling the option and setting
the module parameter. Also update the comment.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Zack Rusin <zackr@vmware.com>
Tested-by: Sui Jingfeng<suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20230320150751.20399-8-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -60,16 +60,17 @@ MODULE_PARM_DESC(drm_fbdev_overalloc,
  * In order to keep user-space compatibility, we want in certain use-cases
  * to keep leaking the fbdev physical address to the user-space program
  * handling the fbdev buffer.
- * This is a bad habit essentially kept into closed source opengl driver
- * that should really be moved into open-source upstream projects instead
- * of using legacy physical addresses in user space to communicate with
- * other out-of-tree kernel modules.
+ *
+ * This is a bad habit, essentially kept to support closed-source OpenGL
+ * drivers that should really be moved into open-source upstream projects
+ * instead of using legacy physical addresses in user space to communicate
+ * with other out-of-tree kernel modules.
  *
  * This module_param *should* be removed as soon as possible and be
  * considered as a broken and legacy behaviour from a modern fbdev device.
  */
-#if IS_ENABLED(CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM)
 static bool drm_leak_fbdev_smem;
+#if IS_ENABLED(CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM)
 module_param_unsafe(drm_leak_fbdev_smem, bool, 0600);
 MODULE_PARM_DESC(drm_leak_fbdev_smem,
 		 "Allow unsafe leaking fbdev physical smem address [default=false]");
@@ -1983,10 +1984,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
 		return ret;
 	}
 
-#if IS_ENABLED(CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM)
-	fb_helper->hint_leak_smem_start = drm_leak_fbdev_smem;
-#endif
-
 	/* push down into drivers */
 	ret = (*fb_helper->funcs->fb_probe)(fb_helper, &sizes);
 	if (ret < 0)
@@ -2185,11 +2182,8 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper)
 
 	info = fb_helper->info;
 	info->var.pixclock = 0;
-	/* Shamelessly allow physical address leaking to userspace */
-#if IS_ENABLED(CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM)
-	if (!fb_helper->hint_leak_smem_start)
-#endif
-		/* don't leak any physical addresses to userspace */
+
+	if (!drm_leak_fbdev_smem)
 		info->flags |= FBINFO_HIDE_SMEM_START;
 
 	/* Need to drop locks to avoid recursive deadlock in

drivers/gpu/drm/drm_fbdev_dma.c

@@ -136,16 +136,9 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 		info->flags |= FBINFO_READS_FAST; /* signal caching */
 	info->screen_size = sizes->surface_height * fb->pitches[0];
 	info->screen_buffer = map.vaddr;
+	info->fix.smem_start = page_to_phys(virt_to_page(info->screen_buffer));
 	info->fix.smem_len = info->screen_size;
 
-#if IS_ENABLED(CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM)
-	/*
-	 * Shamelessly leak the physical address to user-space.
-	 */
-	if (fb_helper->hint_leak_smem_start && !info->fix.smem_start)
-		info->fix.smem_start = page_to_phys(virt_to_page(info->screen_buffer));
-#endif
-
 	return 0;
 
 err_drm_client_buffer_vunmap:

include/drm/drm_fb_helper.h

@@ -195,15 +195,6 @@ struct drm_fb_helper {
 	 */
 	int preferred_bpp;
 
-	/**
-	 * @hint_leak_smem_start:
-	 *
-	 * Hint to the fbdev emulation to store the framebuffer's physical
-	 * address in struct &fb_info.fix.smem_start. If the hint is unset,
-	 * the smem_start field should always be cleared to zero.
-	 */
-	bool hint_leak_smem_start;
-
 #ifdef CONFIG_FB_DEFERRED_IO
 	/**
 	 * @fbdefio: