On 16 December 2015 at 12:44, Ivan T. Ivanov <ivan.iva...@linaro.org> wrote: > >> On Dec 16, 2015, at 12:18 PM, Ulf Hansson <ulf.hans...@linaro.org> wrote: >> >> [...] >> >>>> It seems like a reasonable assumption that the controller can't cope >>>> with a higher clock rate than 100 MHz as "input" clock. That would >>>> then mean that there are different versions of the controller, as it >>>> seems like for some version it's fine with 200MHz and for some 100MHz. >>>> >>>> According to the DT compatible strings, *one* version is currently >>>> supported, "qcom,sdhci-msm-v4"... >>> >>> The same version of hardware is there 4 times. The difference is >>> the maximum clock frequency supported by them is different. In >>> downstream kernels we've handled this by trimming the frequency >>> tables for the different controllers in the clock driver. >>> Setting the clock to INT_MAX will make it run at 400MHz, which >>> doesn't look to be supported by anything besides sdc1 on 8974ac. >>> >>>> >>>> I see two viable solutions. One would be to limit the clock rate >>>> depending on the version of the controller (new compatible strings >>>> needs to be added). Another one would be to limit the clock rate by >>>> using the existing DT binding for max-frequency, and thus do a >>>> clk_set_rate(mmc->f_max) during probe. >>>> >>> >>> I'd rather see that done via OPP tables in DT, but I suppose >>> max-frequency is fine too. We'll need to use OPPs soon enough >>> because there's a voltage associated with that frequency. >>> >>> In case you're wondering, the max frequency for sdc1 on 8974ac is >>> 400MHz. If it's just a plain 8974pro then the max frequency is >>> 200MHz. Otherwise, sdc2 maxes out at 200Mhz and sdc3 and sdc4 max >>> out at 100MHz. >>> >> >> I think we have reached a consensus on the viable options. >> >> As we haven't heard from Ivan, do someone want to send a patch for >> this or shall we just revert $subject patch (which I can deal with)? > > I am following this discussion, but I am not sure what I could do. > > If my understanding is correct, even if controllers report same version, > they don’t support 400MHz core clock.
Correct. > > Initial patch fixes real issue. I am voting for “max-frequency” DT property. I don't have any strong opinion, so I am fine with that approach. That means at ->probe() we need to consider whether "host->f_max" has been obtained via DT (mmc_of_parse() parses the "max-frequency" DT property). If that's the case, we can choose between two solutions. 1) Consider f_max as the correct value to set via clk_set_rate() and if f_max isn't available, fall back to a lower "default" frequency to make sure we are safe. 2) Consider f_max as an upper limit. That means if f_max isn't available we use INT_MAX instead. Both alternatives requires DTB to be updated, but option 1) may be safer as it should allow all cards to be functional, although running in a lower frequency potentially affecting throughput. But again, I don't care much, alternative 2 is okay by me as well. > > I don’t have 8974ac, so I can not test the change. > Let's hope for some help here then! Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
