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authorJon Medhurst (Tixy) <tixy@linaro.org>2014-08-20 13:41:04 +0100
committerTomi Valkeinen <tomi.valkeinen@ti.com>2014-08-26 12:50:27 +0300
commit2b6c53b1504865728a6dfad3e720918a2f89f3a5 (patch)
treed54533ccd807a97d74365e065157dd36a3439991 /drivers/video
parent754d561ab694ff240ad1615abd0d99f3c1db79a2 (diff)
downloadlinux-2b6c53b1504865728a6dfad3e720918a2f89f3a5.tar.bz2
video: ARM CLCD: Fix calculation of bits-per-pixel
If the device-tree specifies a max-memory-bandwidth property then the CLCD driver uses that to calculate the bits-per-pixel supported, however, this calculation is faulty for two reasons. 1. It doesn't ensure that the result is a sane value, i.e. a power of 2 and <= 32 as the rest of the code assumes. 2. It uses the displayed resolution and calculates the average bandwidth across the whole frame. It should instead calculate the peak bandwidth based on the pixel clock. This patch fixes both the above. Signed-off-by: Jon Medhurst <tixy@linaro.org> Acked-by: Pawel Moll <pawel.moll@arm.com> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Diffstat (limited to 'drivers/video')
-rw-r--r--drivers/video/fbdev/amba-clcd.c23
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;