drm/fsl-dcu: introduce kernel parameter to specify fbdev depth

Add a kernel parameter legancyfb_depth (like the i.MX drm driver)
to control the legancy fbdev depth. Default to the so far hard
coded depth of 24-bit. Currently changing the framebuffer depth
is not possible from user space when using the fbdev emulation
layer... This provides a rudimentary mechanism to change depth
without having to change kernel code.

Signed-off-by: Stefan Agner <stefan@agner.ch>

1 files changed, 15 insertions, 1 deletions

diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
index 736451616ce4..58ccacaf5a4e 100644
--- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
+++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
@@ -32,6 +32,9 @@
 #include "fsl_dcu_drm_drv.h"
 #include "fsl_tcon.h"
 
+static int legacyfb_depth = 24;
+module_param(legacyfb_depth, int, 0444);
+
 static bool fsl_dcu_drm_is_volatile_reg(struct device *dev, unsigned int reg)
 {
         if (reg == DCU_INT_STATUS || reg == DCU_UPDATE_MODE)
@@ -87,7 +90,18 @@ static int fsl_dcu_load(struct drm_device *dev, unsigned long flags)
                 goto done;
         dev->irq_enabled = true;
 
-        fsl_dev->fbdev = drm_fbdev_cma_init(dev, 24, 1, 1);
+        if (legacyfb_depth != 16 && legacyfb_depth != 24 &&
+            legacyfb_depth != 32) {
+                dev_warn(dev->dev,
+                        "Invalid legacyfb_depth.  Defaulting to 24bpp\n");
+                legacyfb_depth = 24;
+        }
+        fsl_dev->fbdev = drm_fbdev_cma_init(dev, legacyfb_depth, 1, 1);
+        if (IS_ERR(fsl_dev->fbdev)) {
+                ret = PTR_ERR(fsl_dev->fbdev);
+                fsl_dev->fbdev = NULL;
+                goto done;
+        }
 
         return 0;
 done: