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

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

[Jean Delvare]

The VESA specification suggests a 2.2 ms timeout on DDC channels.
Use exactly that (as the i915 driver does) instead of hard-coding a
jiffy count.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Keith Packard <keithp@keithp.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Alex Deucher <alexdeucher@gmail.com>
---
Already sent on: 2011-10-21.

 drivers/gpu/drm/radeon/radeon_i2c.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
--- linux-3.3-rc1.orig/drivers/gpu/drm/radeon/radeon_i2c.c	2012-01-28 10:37:51.722069517 +0100
+++ linux-3.3-rc1/drivers/gpu/drm/radeon/radeon_i2c.c	2012-01-28 10:39:26.996070929 +0100
@@ -925,9 +925,7 @@ 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/radeon/kms: Use the standard VESA timeout for DDC channels

[Alex Deucher]

On Sat, Jan 28, 2012 at 5:08 AM, Jean Delvare <jdelvare@suse.de> wrote:
> The VESA specification suggests a 2.2 ms timeout on DDC channels.
> Use exactly that (as the i915 driver does) instead of hard-coding a
> jiffy count.
>
> Signed-off-by: Jean Delvare <jdelvare@suse.de>
> Reviewed-by: Keith Packard <keithp@keithp.com>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Alex Deucher <alexdeucher@gmail.com>

Reviewed-by: Alex Deucher <alexdeucher@gmail.com>

> ---
> Already sent on: 2011-10-21.
>
>  drivers/gpu/drm/radeon/radeon_i2c.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> --- linux-3.3-rc1.orig/drivers/gpu/drm/radeon/radeon_i2c.c      2012-01-28 10:37:51.722069517 +0100
> +++ linux-3.3-rc1/drivers/gpu/drm/radeon/radeon_i2c.c   2012-01-28 10:39:26.996070929 +0100
> @@ -925,9 +925,7 @@ 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/radeon/kms: Use the standard VESA timeout for DDC channels

[Keith Packard]

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On Sat, 28 Jan 2012 11:08:58 +0100, Jean Delvare <jdelvare@suse.de> wrote:

> The VESA specification suggests a 2.2 ms timeout on DDC channels.
> Use exactly that (as the i915 driver does) instead of hard-coding a
> jiffy count.

The Vesa spec seems to say 2ms; at least according to the DDC/CI spec
paragraph 6.6. usecs_to_jiffies rounds the value it gets up, so we
should never get an interval less than 2ms if we pass 2000us to it.

-- 
keith.packard@intel.com

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

[Jean Delvare]

Hi Keith,

On Sunday 29 January 2012 02:34:05 am Keith Packard wrote:
> On Sat, 28 Jan 2012 11:08:58 +0100, Jean Delvare <jdelvare@suse.de>
> wrote:
> > The VESA specification suggests a 2.2 ms timeout on DDC channels.
> > Use exactly that (as the i915 driver does) instead of hard-coding a
> > jiffy count.
> 
> The Vesa spec seems to say 2ms; at least according to the DDC/CI spec
> paragraph 6.6.

To be honest, I did not read it, I don't even think it is publicly 
available, is it? I did naively trust the comment in radeon_i2c.c: "vesa 
says 2.2 ms is enough". Not sure where this value came from if you claim 
the spec says 2 ms. Jerome, you wrote this comment in the first place, 
want to comment on that?

The Intel drivers are using 2.2 ms too, since November 2008 (added to 
i915 driver by Jesse Barnes.) Maybe this all originates from X11 driver 
code?

> usecs_to_jiffies rounds the value it gets up, so we
> should never get an interval less than 2ms if we pass 2000us to it.

Technically I agree, all we need to agree on is the value, 2000 us or 
2200 us. I don't mind either way, I am not aware of specific complaints 
about the current code, I was just trying to clean things up, as hard-
coding jiffy counts is bad and having different timeouts in the various 
drivers makes little sense IMHO.

-- 
Jean Delvare
Suse L3