On Mon, 2009-10-05 at 10:29 +0200, Jean Delvare wrote: > On Sun, 04 Oct 2009 21:54:37 -0400, Andy Walls wrote: > > On Mon, 2009-10-05 at 01:23 +0300, Aleksandr V. Piskunov wrote: > > > > > > So question is: > > > 1) Is it ok to decrease udelay for this board? > > > > Sure, I think. It would actually run the ivtv I2C bus at the nominal > > clock rate specified by the I2C specification. > > FWIW, 100 kHz isn't the "nominal" I2C clock rate, but the maximum clock > rate for normal I2C. It is perfectly valid to run I2C buses as lower > clock frequencies. I don't even think there is a minimum for I2C (but > there is a minimum of 10 kHz for SMBus.) Ah, thanks. I was too lazy to go read my copy of the spec. > But of course different hardware implementations may not fully cover > the standard I2C or SMBus frequency range, and it is possible that a TV > adapter manufacturer designed its hardware to run the I2C bus at a > fixed frequency and we have to use that frequency to make the adapter > happy. This is very plausible for a microcontroller implementation of an I2C slave, which is the case here. > > I never had any reason to change it, as I feared causing regressions in > > many well tested boards. > > This is a possibility, indeed. But for obvious performance reasons, I'd > rather use 100 kHz as the default, and let boards override it with a > lower frequency of their choice if needed. Obviously this provides an > easy improvement path, where each board can be tested separately and > I2C bus frequency bumped from 50 kHz to 100 kHz after some good testing. > > Some boards might even support fast I2C, up to 400 kHz but limited to > 250 kHz by the i2c-algo-bit implementation. I can add a module option to ivtv for I2C clock rate. It may take a few days. Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
