From: Keith Packard <keithp@keithp.com>
To: Jean Delvare <jdelvare@suse.de>, dri-devel@lists.freedesktop.org
Cc: Eugeni Dodonov <eugeni.dodonov@intel.com>
Subject: Re: [PATCH 1/2] drm/kms: Make i2c buses faster
Date: Sat, 28 Jan 2012 17:26:25 -0800 [thread overview]
Message-ID: <86sjizqoxq.fsf@sumi.keithp.com> (raw)
In-Reply-To: <201201281107.09266.jdelvare@suse.de>
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On Sat, 28 Jan 2012 11:07:09 +0100, 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.
That runs the DDC at a whopping 50kbps, which is half of the maximum
rate specified in the DDC/CI standard. I don't know if we can count on
clock stretching (http://www.i2c-bus.org/clock-stretching/), but if so,
I don't know why we wouldn't just go to the standard 100kbps data rate
and be done with it.
Might be nice to see what frequency Windows uses for i2c; anyone want to
pull a vga cable apart and hook up a logic analyser?
--
keith.packard@intel.com
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next prev parent reply other threads:[~2012-01-29 1:26 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-28 10:07 [PATCH 1/2] drm/kms: Make i2c buses faster Jean Delvare
2012-01-28 14:46 ` Alex Deucher
2012-01-29 1:26 ` Keith Packard [this message]
2012-03-21 10:45 ` Jean Delvare
-- strict thread matches above, loose matches on Subject: below --
2011-10-21 7:08 Jean Delvare
2011-10-21 13:32 ` Alan Cox
2011-10-21 14:16 ` Jean Delvare
2011-10-21 18:05 ` Alex Deucher
2011-10-21 19:29 ` Jean Delvare
2011-10-22 14:38 ` Alex Deucher
2011-10-24 14:19 ` Eugeni Dodonov
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