All of lore.kernel.org
 help / color / mirror / Atom feed
From: "Jon Medhurst (Tixy)" <tixy@linaro.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: linux-fbdev@vger.kernel.org, Pawel Moll <Pawel.Moll@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] video: ARM CLCD: Fix calculation of bits-per-pixel
Date: Wed, 20 Aug 2014 13:41:04 +0100	[thread overview]
Message-ID: <1408538464.3858.43.camel@linaro1.home> (raw)

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>
---

Changes since v1:
- Changed formula for calculating bits per pixel
- Changed commit message and subject, was:
  "video: ARM CLCD: Ensure bits-per-pixel is a power of 2 and <= 32"

 drivers/video/fbdev/amba-clcd.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/amba-clcd.c b/drivers/video/fbdev/amba-clcd.c
index beadd3e..a7b6217 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;
-- 
2.1.0.rc1




WARNING: multiple messages have this Message-ID (diff)
From: "Jon Medhurst (Tixy)" <tixy@linaro.org>
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] video: ARM CLCD: Fix calculation of bits-per-pixel
Date: Wed, 20 Aug 2014 12:41:04 +0000	[thread overview]
Message-ID: <1408538464.3858.43.camel@linaro1.home> (raw)

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>
---

Changes since v1:
- Changed formula for calculating bits per pixel
- Changed commit message and subject, was:
  "video: ARM CLCD: Ensure bits-per-pixel is a power of 2 and <= 32"

 drivers/video/fbdev/amba-clcd.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/amba-clcd.c b/drivers/video/fbdev/amba-clcd.c
index beadd3e..a7b6217 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;
-- 
2.1.0.rc1




WARNING: multiple messages have this Message-ID (diff)
From: tixy@linaro.org (Jon Medhurst (Tixy))
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] video: ARM CLCD: Fix calculation of bits-per-pixel
Date: Wed, 20 Aug 2014 13:41:04 +0100	[thread overview]
Message-ID: <1408538464.3858.43.camel@linaro1.home> (raw)

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>
---

Changes since v1:
- Changed formula for calculating bits per pixel
- Changed commit message and subject, was:
  "video: ARM CLCD: Ensure bits-per-pixel is a power of 2 and <= 32"

 drivers/video/fbdev/amba-clcd.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/amba-clcd.c b/drivers/video/fbdev/amba-clcd.c
index beadd3e..a7b6217 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;
-- 
2.1.0.rc1

             reply	other threads:[~2014-08-20 12:41 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-20 12:41 Jon Medhurst (Tixy) [this message]
2014-08-20 12:41 ` [PATCH v2] video: ARM CLCD: Fix calculation of bits-per-pixel Jon Medhurst (Tixy)
2014-08-20 12:41 ` Jon Medhurst (Tixy)
2014-08-20 13:03 ` Pawel Moll
2014-08-20 13:03   ` Pawel Moll
2014-08-20 13:03   ` Pawel Moll
2014-08-26  9:52 ` Tomi Valkeinen
2014-08-26  9:52   ` Tomi Valkeinen
2014-08-26  9:52   ` Tomi Valkeinen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1408538464.3858.43.camel@linaro1.home \
    --to=tixy@linaro.org \
    --cc=Pawel.Moll@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-fbdev@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@arm.linux.org.uk \
    --cc=plagnioj@jcrosoft.com \
    --cc=tomi.valkeinen@ti.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.