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Message-ID: <53849DD7.1070202@linaro.org> Date: Tue, 27 May 2014 15:14:47 +0100 From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org> To: Ulf Hansson <ulf.hansson@...aro.org> CC: Russell King <linux@....linux.org.uk>, linux-mmc <linux-mmc@...r.kernel.org>, Chris Ball <chris@...ntf.net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-arm-msm@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org> Subject: Re: [PATCH v3 12/13] mmc: mmci: add explicit clk control On 27/05/14 15:07, Ulf Hansson wrote: >>> Hmm. Looking a bit deeper into this, we have some additional related >>> code to fixup. :-) >>> >>> In ->probe(), we do clk_set_rate(100MHz), if the mclk > 100MHz. That's >>> due to the current variants don't support higher frequency than this. >>> It seems like the Qcom variant may support up to 208MHz? Now, if >>> that's the case, we need to add "f_max" to the struct variant_data to >>> store this information, so we can respect different values while doing >>> clk_set_rate() at ->probe(). >>> >> Yes, qcom SOCs support more than 100Hhz clock. >> >> Probe and clk_set_rate/set_ios should respect this. >> >> On the other thought, Should probe actually care about clocks which are >> explicitly controlled? It should not even attempt to set any frequency to >> start with. > > The 100 MHz is related to constraints set by the specification of the > IP block, not the MMC/SD/SDIO spec. > > Thus at ->probe() we must perform the clk_set_rate(). I agree its valid for controllers which have this constraints. > >> mmc-core would set the right frequency depending on the mmc >> state-machine respecting f_min and f_max. >> I think for qcom, probe should just check the if f_max and f_min are valid >> and set them to defaults if any in the same lines as existing code. >> >> >>> While updating mmc->f_max for host->variant->explicit_mclk_control, we >>> shouldn't care about using the host->mclk as a limiter, instead, use >>> min(mmc->f_max, host->variant->f_max) and fallback to fmax. >>> >> Yes, that's correct, mclk should not be used as limiter. Adding f_max to the >> variant looks useful. >> >> >>> Not sure how that will affect the logic. :-) >>> >>>> >>>> >>>>> Additionally, this makes me wonder about f_min. I haven't seen >>>>> anywhere in this patch were that value is being set to proper value, >>>>> right? >>>>> >>>> >>>> f_min should be 400000 for qcom, I think with the default mclk frequency >>>> and >>>> a divider of 512 used for calculating the f_min is bringing down the >>>> f_min >>>> to lessthan 400Kz. Which is why its working fine. >>>> I think the possibility of mclk default frequency being greater than >>>> 208Mhz >>>> is very less. so I could either leave it as it is Or force this to 400000 >>>> all the time for qcom chips. >>> >>> >>> No, this seems like a wrong approach. >>> >>> I think you would like to do use the clk_round_rate() find out the >>> lowest possible rate. Or just use a fixed fallback value somehow. >> >> >> clk_round_rate(mclk, 0) might be more generic, instead of fixed fallback. >> Let the mmc-core figure out what frequency would be best from its table >> starting from f_min. > > Agree! > > clk_round_rate(mclk, 100KHz), might be better though - since that is > actually the lowest request frequency whatsoever. > Perfect. --srini > Kind regards > Ulf Hansson > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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