Commit 2b6c53b1 authored by Jon Medhurst (Tixy)'s avatar Jon Medhurst (Tixy) Committed by Tomi Valkeinen
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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: default avatarJon Medhurst <tixy@linaro.org>
Acked-by: default avatarPawel Moll <pawel.moll@arm.com>
Signed-off-by: default avatarTomi Valkeinen <tomi.valkeinen@ti.com>
parent 754d561a

drivers/video/fbdev/amba-clcd.c

+18 −5
Original line number Diff line number Diff line
@@ -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;

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