1 files changed, 18 insertions, 5 deletions

diff --git a/drivers/video/fbdev/amba-clcd.c b/drivers/video/fbdev/amba-clcd.c
index beadd3edaa17..a7b6217ac87b 100644
--- a/drivers/video/fbdev/amba-clcd.c
+++ b/drivers/video/fbdev/amba-clcd.c
@@ -24,6 +24,7 @@
 #include <linux/list.h>
 #include <linux/amba/bus.h>
 #include <linux/amba/clcd.h>
+#include <linux/bitops.h>
 #include <linux/clk.h>
 #include <linux/hardirq.h>
 #include <linux/dma-mapping.h>
@@ -650,6 +651,7 @@ static int clcdfb_of_init_display(struct clcd_fb *fb)
 {
         struct device_node *endpoint;
         int err;
+        unsigned int bpp;
         u32 max_bandwidth;
         u32 tft_r0b0g0[3];
 
@@ -667,11 +669,22 @@ static int clcdfb_of_init_display(struct clcd_fb *fb)
 
         err = of_property_read_u32(fb->dev->dev.of_node, "max-memory-bandwidth",
                         &max_bandwidth);
-        if (!err)
-                fb->panel->bpp = 8 * max_bandwidth / (fb->panel->mode.xres *
-                                fb->panel->mode.yres * fb->panel->mode.refresh);
-        else
-                fb->panel->bpp = 32;
+        if (!err) {
+                /*
+                 * max_bandwidth is in bytes per second and pixclock in
+                 * pico-seconds, so the maximum allowed bits per pixel is
+                 *   8 * max_bandwidth / (PICOS2KHZ(pixclock) * 1000)
+                 * Rearrange this calculation to avoid overflow and then ensure
+                 * result is a valid format.
+                 */
+                bpp = max_bandwidth / (1000 / 8)
+                        / PICOS2KHZ(fb->panel->mode.pixclock);
+                bpp = rounddown_pow_of_two(bpp);
+                if (bpp > 32)
+                        bpp = 32;
+        } else
+                bpp = 32;
+        fb->panel->bpp = bpp;
 
 #ifdef CONFIG_CPU_BIG_ENDIAN
         fb->panel->cntl |= CNTL_BEBO;