A udelay value of 20 leads to an I2C bus running at only 25 kbps. I2C devices can typically operate faster than this, 50 kbps should be fine for all devices (and compliant devices can always stretch the clock if needed.)
FWIW, the vast majority of framebuffer drivers set udelay to 10 already. So set it to 10 in DRM drivers too, this will make EDID block reads faster. We might even lower the udelay value later if no problem is reported.
Signed-off-by: Jean Delvare jdelvare@suse.de Reviewed-by: Alex Deucher alexdeucher@gmail.com Cc: Dave Airlie airlied@gmail.com --- Changes since v1: * Split per driver to make merging easier. * Make the subject line more accurate.
drivers/gpu/drm/radeon/radeon_i2c.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-3.4-rc0.orig/drivers/gpu/drm/radeon/radeon_i2c.c 2012-03-21 13:43:33.753915151 +0100 +++ linux-3.4-rc0/drivers/gpu/drm/radeon/radeon_i2c.c 2012-03-21 13:48:01.619472673 +0100 @@ -925,7 +925,7 @@ struct radeon_i2c_chan *radeon_i2c_creat i2c->algo.bit.setscl = set_clock; i2c->algo.bit.getsda = get_data; i2c->algo.bit.getscl = get_clock; - i2c->algo.bit.udelay = 20; + 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;
On Wed, Mar 21, 2012 at 9:30 AM, Jean Delvare jdelvare@suse.de wrote:
A udelay value of 20 leads to an I2C bus running at only 25 kbps. I2C devices can typically operate faster than this, 50 kbps should be fine for all devices (and compliant devices can always stretch the clock if needed.)
FWIW, the vast majority of framebuffer drivers set udelay to 10 already. So set it to 10 in DRM drivers too, this will make EDID block reads faster. We might even lower the udelay value later if no problem is reported.
FWIW, our proprietary code uses 50 khz for i2c. So I think it should be fine.
Alex
Signed-off-by: Jean Delvare jdelvare@suse.de Reviewed-by: Alex Deucher alexdeucher@gmail.com Cc: Dave Airlie airlied@gmail.com
Changes since v1:
- Split per driver to make merging easier.
- Make the subject line more accurate.
drivers/gpu/drm/radeon/radeon_i2c.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-3.4-rc0.orig/drivers/gpu/drm/radeon/radeon_i2c.c 2012-03-21 13:43:33.753915151 +0100 +++ linux-3.4-rc0/drivers/gpu/drm/radeon/radeon_i2c.c 2012-03-21 13:48:01.619472673 +0100 @@ -925,7 +925,7 @@ struct radeon_i2c_chan *radeon_i2c_creat i2c->algo.bit.setscl = set_clock; i2c->algo.bit.getsda = get_data; i2c->algo.bit.getscl = get_clock;
- i2c->algo.bit.udelay = 20;
- 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;
-- Jean Delvare Suse L3
dri-devel@lists.freedesktop.org
-
Alex Deucher -
Jean Delvare