Hi Haavard, On Wed, Sep 15, 2010 at 12:51:38PM +0200, Haavard Skinnemoen wrote: > Thanks for the references. IMO Hein's patch is overkill. There is > absolutely no reason why 200 kHz should be a problem on any setup, and > I haven't found any indication in any discussions that it is. Pierre was worried that we'd ping-pong between having an f_min too high for some cards and too low for others, and be breaking a new set of cards each time we changed the value. He may have been being overly pessimistic, but I don't think being cautious comes with any significant downsides here. There's also a (small) performance concern when f_min gets low, though I agree that it wouldn't be a problem at 200 kHz. > The reason why fOD was set to 400 kHz in the first place is that some > controllers have a very low f_min so running the initialization at that > frequency causes problems. Which makes sense because the SD standard > clearly says that the clock can't be slower than 100 kHz. > > But I have never seen any reasons why we absolutely _have_ to run the > clock at the maximum frequency allowed by the spec. In fact, Sascha > Hauer, who was the one who changed the minimum clock frequency to 400 > kHz, said he would be fine with any frequency between 50 kHz and 400 > kHz [1]. I agree that we aren't trying to run at the maximum possible frequency, just trying to avoid having to choose a single perfect value without enough information on what it is. Thanks, -- Chris Ball <cjb@xxxxxxxxxx> <http://printf.net/> One Laptop Per Child -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
