drm/cirrus: Limit modes depending on bpp option

The commit [8975626ea35a: drm/cirrus: allow 32bpp framebuffers for
cirrus drm] broke X modesetting driver because cirrus driver still
provides the full list of modes up to 1280x1024 while the 32bpp can
support only up to 800x600.

We might be able to filter out the invalid modes in mode_valid
callback, but unfortunately the bpp in question can't be referred
there for now (let me know if there is a better way to retrieve the
bpp for the probed fb).

So, instead, this patch adds the bpp module option to specify the
maximal bpp explicitly and limits the resolutions in get_modes
depending on its value.

The default value is set to 24 so that the existing stuff keeps
working.  If you need a new 32bpp feature, specify cirrus.bpp=32
option explicitly.

Fixes: 8975626ea35a ('drm/cirrus: allow 32bpp framebuffers for cirrus drm')
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/cirrus/cirrus_drv.c

@@ -16,9 +16,12 @@
 #include "cirrus_drv.h"
 
 int cirrus_modeset = -1;
+int cirrus_bpp = 24;
 
 MODULE_PARM_DESC(modeset, "Disable/Enable modesetting");
 module_param_named(modeset, cirrus_modeset, int, 0400);
+MODULE_PARM_DESC(bpp, "Max bits-per-pixel (default:24)");
+module_param_named(bpp, cirrus_bpp, int, 0400);
 
 /*
  * This is the generic driver code. This binds the driver to the drm core,

drivers/gpu/drm/cirrus/cirrus_drv.h

@@ -262,4 +262,7 @@ static inline void cirrus_bo_unreserve(struct cirrus_bo *bo)
 
 int cirrus_bo_push_sysram(struct cirrus_bo *bo);
 int cirrus_bo_pin(struct cirrus_bo *bo, u32 pl_flag, u64 *gpu_addr);
+
+extern int cirrus_bpp;
+
 #endif				/* __CIRRUS_DRV_H__ */

drivers/gpu/drm/cirrus/cirrus_main.c

@@ -320,6 +320,8 @@ bool cirrus_check_framebuffer(struct cirrus_device *cdev, int width, int height,
 	const int max_pitch = 0x1FF << 3; /* (4096 - 1) & ~111b bytes */
 	const int max_size = cdev->mc.vram_size;
 
+	if (bpp > cirrus_bpp)
+		return false;
 	if (bpp > 32)
 		return false;
 

drivers/gpu/drm/cirrus/cirrus_mode.c

@@ -501,8 +501,13 @@ static int cirrus_vga_get_modes(struct drm_connector *connector)
 	int count;
 
 	/* Just add a static list of modes */
-	count = drm_add_modes_noedid(connector, 1280, 1024);
-	drm_set_preferred_mode(connector, 1024, 768);
+	if (cirrus_bpp <= 24) {
+		count = drm_add_modes_noedid(connector, 1280, 1024);
+		drm_set_preferred_mode(connector, 1024, 768);
+	} else {
+		count = drm_add_modes_noedid(connector, 800, 600);
+		drm_set_preferred_mode(connector, 800, 600);
+	}
 	return count;
 }