> 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. Initial patch fixes real issue. I am voting for “max-frequency” DT property. I don’t have 8974ac, so I can not test the change. Regards, Ivan -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
