Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932914AbbLPNti (ORCPT ); Wed, 16 Dec 2015 08:49:38 -0500 Received: from mail-qk0-f170.google.com ([209.85.220.170]:35688 "EHLO mail-qk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753894AbbLPNtg convert rfc822-to-8bit (ORCPT ); Wed, 16 Dec 2015 08:49:36 -0500 MIME-Version: 1.0 In-Reply-To: <942B071D-D7F6-4D20-916C-BBE9096146E9@linaro.org> References: <1436183618-15330-1-git-send-email-ivan.ivanov@linaro.org> <20151106233913.GB30882@usrtlx11787.corpusers.net> <20151110201841.GB24116@codeaurora.org> <942B071D-D7F6-4D20-916C-BBE9096146E9@linaro.org> Date: Wed, 16 Dec 2015 14:49:35 +0100 Message-ID: Subject: Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock From: Ulf Hansson To: "Ivan T. Ivanov" Cc: Stephen Boyd , Bjorn Andersson , Georgi Djakov , Bjorn Andersson , Peter Griffin , linux-mmc , "linux-kernel@vger.kernel.org" , linux-arm-msm Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3412 Lines: 86 On 16 December 2015 at 12:44, Ivan T. Ivanov wrote: > >> On Dec 16, 2015, at 12:18 PM, Ulf Hansson 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-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/