On Mon, 26 Mar 2012, Guennadi Liakhovetski wrote: > On Mon, 26 Mar 2012, Magnus Damm wrote: > > > On Mon, Mar 26, 2012 at 2:52 PM, Simon Horman <horms@xxxxxxxxxxxx> wrote: > > > On Mon, Mar 26, 2012 at 02:45:30PM +0900, Yusuke Goda wrote: > > >> Hi Simon-san, Guennadi-san > > >> > > >> (2012/03/26 7:30), Simon Horman wrote: > > >> > On Sat, Mar 24, 2012 at 07:06:31PM +0100, Guennadi Liakhovetski wrote: > > >> >> On Wed, 21 Mar 2012, Simon Horman wrote: > > >> >> > > >> >>> mmc->f_max should be half of the bus clock. > > >> >>> And now that mmc->f_max is not equal to the bus clock the > > >> >>> latter should be used directly to calculate mmc->f_min. > > >> >> > > >> >> The patch seems correct as it stands, however, looking at it - does anyone > > >> >> understands why that "close to 400kHz" comment and such a complicated > > >> >> calculation? Shouldn't it be just host->clk / 512 always? Maybe this > > >> >> should be a separate patch, so, for this one > > >> >> > > >> >> Acked-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> > > >> > > > >> > Hi Guennadi, > > >> > > > >> > that code seems to date back to the original driver submission > > >> > made by Goda-san. I have CCed him as perhaps he recalls why > > >> > the code is like it is. > > >> I thought to get closer to 400kHz if possible. > > >> Probably even host->clk / 512 does not have any problem. > > > > > > Sorry for my ignorance, is ~400kHz desirable for some reason? > > > > The 400kHz frequency is used during initialization of the SD card. > > Simply put, the SD frequency starts low out low and is then changed to > > something higher depending on the capability of the memory card and > > the host controller. Please have a look at the simplified SD > > specification for more details. > > I see, so, we want something like > > shift = fls(host->clk / 400000 - 1); > mmc->f_min = host->clk >> shift; > > eventually with some rounding, depending on our preferences. As you see in the email header, that last email was sent about 24 hours ago, it just got stuck on my mail server due to some local problem... After the recent discussions on this topic, this mail is outdated and should be disregarded. I certainly agree to using clk / 512 unconditionally for all host frequencies, which also was my original suggestion in http://article.gmane.org/gmane.linux.kernel.mmc/13556 Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- 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
