[PATCH 2/2] drm/kms: Use the standard VESA timeout for DDC channels

[PATCH 2/2] drm/kms: Use the standard VESA timeout for DDC channels

[Jean Delvare]

The VESA specification suggests a 2.2 ms timeout on DDC channels.
Only the intel DRM driver implements this properly today, align all
drivers to the proper implementation.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Eugeni Dodonov <eugeni@dodonov.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Keith Packard <keithp@keithp.com>
Cc: Alex Deucher <alexdeucher@gmail.com>
---
 drivers/gpu/drm/i915/intel_i2c.c      |    2 +-
 drivers/gpu/drm/nouveau/nouveau_i2c.c |    2 +-
 drivers/gpu/drm/radeon/radeon_i2c.c   |    4 +---
 3 files changed, 3 insertions(+), 5 deletions(-)

--- linux-3.1-rc10.orig/drivers/gpu/drm/i915/intel_i2c.c	2011-10-20 14:59:11.000000000 +0200
+++ linux-3.1-rc10/drivers/gpu/drm/i915/intel_i2c.c	2011-10-20 15:24:33.000000000 +0200
@@ -183,7 +183,7 @@ intel_gpio_create(struct drm_i915_privat
 	gpio->algo.getsda = get_data;
 	gpio->algo.getscl = get_clock;
 	gpio->algo.udelay = I2C_RISEFALL_TIME;
-	gpio->algo.timeout = usecs_to_jiffies(2200);
+	gpio->algo.timeout = usecs_to_jiffies(2200);	/* from VESA */
 	gpio->algo.data = gpio;
 
 	if (i2c_bit_add_bus(&gpio->adapter))
--- linux-3.1-rc10.orig/drivers/gpu/drm/nouveau/nouveau_i2c.c	2011-10-20 15:14:36.000000000 +0200
+++ linux-3.1-rc10/drivers/gpu/drm/nouveau/nouveau_i2c.c	2011-10-20 15:24:37.000000000 +0200
@@ -218,7 +218,7 @@ nouveau_i2c_init(struct drm_device *dev,
 	if (entry->port_type < 6) {
 		i2c->adapter.algo_data = &i2c->bit;
 		i2c->bit.udelay = 10;
-		i2c->bit.timeout = usecs_to_jiffies(5000);
+		i2c->bit.timeout = usecs_to_jiffies(2200);	/* from VESA */
 		i2c->bit.data = i2c;
 		ret = i2c_bit_add_bus(&i2c->adapter);
 	} else {
--- linux-3.1-rc10.orig/drivers/gpu/drm/radeon/radeon_i2c.c	2011-10-20 14:58:17.000000000 +0200
+++ linux-3.1-rc10/drivers/gpu/drm/radeon/radeon_i2c.c	2011-10-20 15:24:41.000000000 +0200
@@ -929,9 +929,7 @@ struct radeon_i2c_chan *radeon_i2c_creat
 		i2c->algo.bit.getsda = get_data;
 		i2c->algo.bit.getscl = get_clock;
 		i2c->algo.bit.udelay = 10;
-		/* vesa says 2.2 ms is enough, 1 jiffy doesn't seem to always
-		 * make this, 2 jiffies is a lot more reliable */
-		i2c->algo.bit.timeout = 2;
+		i2c->algo.bit.timeout = usecs_to_jiffies(2200);	/* from VESA */
 		i2c->algo.bit.data = i2c;
 		ret = i2c_bit_add_bus(&i2c->adapter);
 		if (ret) {

-- 
Jean Delvare
Suse L3

Re: [PATCH 2/2] drm/kms: Use the standard VESA timeout for DDC channels

[Keith Packard]

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On Fri, 21 Oct 2011 09:10:12 +0200, Jean Delvare <jdelvare@suse.de> wrote:

> -		/* vesa says 2.2 ms is enough, 1 jiffy doesn't seem to always
> -		 * make this, 2 jiffies is a lot more reliable */
> -		i2c->algo.bit.timeout = 2;
> +		i2c->algo.bit.timeout = usecs_to_jiffies(2200);	/* from VESA */

From my reading of the usecs_to_jiffies code, it always returns a time
at least as long as requested, so this will ensure that you're waiting
at least 2.2ms, unlike 2 jiffies which is some random amount of time
depending on the HZ setting in the kernel.

Reviewed-by: Keith Packard <keithp@keithp.com>

-- 
keith.packard@intel.com

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