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[209.132.180.67]) by mx.google.com with ESMTP id j7-v6si23182521pgj.532.2018.10.30.06.44.21; Tue, 30 Oct 2018 06:44:38 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728178AbeJ3WfS (ORCPT + 99 others); Tue, 30 Oct 2018 18:35:18 -0400 Received: from mail-sh2.amlogic.com ([58.32.228.45]:48908 "EHLO mail-sh2.amlogic.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727450AbeJ3WfS (ORCPT ); Tue, 30 Oct 2018 18:35:18 -0400 Received: from [10.18.29.185] (10.18.29.185) by mail-sh2.amlogic.com (10.18.11.6) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Tue, 30 Oct 2018 21:41:38 +0800 Subject: Re: [PATCH v5 3/3] clk: meson: add sub MMC clock controller driver To: Jerome Brunet , Martin Blumenstingl CC: Neil Armstrong , , , , , , , , , , , , , , , , , References: <1539839245-13793-1-git-send-email-jianxin.pan@amlogic.com> <1539839245-13793-4-git-send-email-jianxin.pan@amlogic.com> <3723695d951e0d30e8a0117d336d8f268269a030.camel@baylibre.com> From: Jianxin Pan Message-ID: <79e2e947-ea85-5f39-13b0-f5c67aff5949@amlogic.com> Date: Tue, 30 Oct 2018 21:41:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <3723695d951e0d30e8a0117d336d8f268269a030.camel@baylibre.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.18.29.185] X-ClientProxiedBy: mail-sh2.amlogic.com (10.18.11.6) To mail-sh2.amlogic.com (10.18.11.6) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jerome, On 2018/10/29 3:16, Jerome Brunet wrote: > On Thu, 2018-10-25 at 22:58 +0200, Martin Blumenstingl wrote: >> Hi Jerome, >> >> On Thu, Oct 25, 2018 at 2:54 PM Jerome Brunet wrote: >> [snip] >>>>>> +static void clk_regmap_div_init(struct clk_hw *hw) >>>>>> +{ >>>>>> + struct clk_regmap *clk = to_clk_regmap(hw); >>>>>> + struct clk_regmap_div_data *div = clk_get_regmap_div_data(clk); >>>>>> + unsigned int val; >>>>>> + int ret; >>>>>> + >>>>>> + ret = regmap_read(clk->map, div->offset, &val); >>>>>> + if (ret) >>>>>> + return; >>>>>> >>>>>> + val &= (clk_div_mask(div->width) << div->shift); >>>>>> + if (!val) >>>>>> + regmap_update_bits(clk->map, div->offset, >>>>>> + clk_div_mask(div->width) << div->shift, >>>>>> + clk_div_mask(div->width)); >>>>> >>>>> This is wrong for several reasons: >>>>> * You should hard code the initial value in the driver. >>>>> * If shift is not 0, I doubt this will give the expected result. >>>> >>>> The value 0x00 of divider means nand clock off then read/write nand register is forbidden. >>> >>> That is not entirely true, you can access the clock register or you'd be in a >>> chicken and egg situation. >>> >>>> Should we set the initial value in nand driver, or in sub emmc clk driver? >>> >>> In the nand driver, which is the consumer of the clock. see my previous comments >>> about it. >> >> an old version of this series had the code still in the NAND driver >> (by writing to the registers directly instead of using the clk API). >> this looks pretty much like a "sclk-div" to me (as I commented in v3 >> of this series: [0]): >> - value 0 means disabled >> - positive divider values >> - (probably no duty control, but that's optional as far as I >> understand sclk-div) >> - uses max divider value when enabling the clock >> >> if switching to sclk-div works then we can get rid of some duplicate code > > It is possible: > There is a couple of things to note though: > > * sclk does not 'uses max divider value when enabling the clock': Since this > divider can gate, it needs to save the divider value when disabling, since the > divider value is no longer stored in the register, > On init, this cached value is saved as it is. If the divider is initially > disabled, we have to set the cached value to something that makes sense, in case > the clock is enabled without a prior call to clk_set_rate(). > > So in sclk, the clock setting is not changed nor hard coded in init, and this is > a very important difference. > > * Even if sclk zero value means gated, it is still a zero based divider, while > eMMC/Nand divider is one based. It this controller was to sclk, then something > needs to be done for this. > > * Since sclk caches a value in its data, and there can multiple instance of eMMC > /NAND clock controller, some care must be taken when registering the data. > > Both the generic divider and sclk could work here ... it's up to you Jianxin. Thank you for the detailed explanation. I will use sclk here. With generic divider, there is a WARNING in divider_recalc_rate() durning clk_register(): [ 0.918238] ffe05000.clock-controller#div: Zero divisor and CLK_DIVIDER_ALLOW_ZERO not set [ 0.925581] WARNING: CPU: 3 PID: 1 at drivers/clk/clk-divider.c:127 divider_recalc_rate+0x88/0x90 Then I still need to hard code the initual value, or add CLK_DIVIDER_ALLOW_ZERO flags. > >> >> >> Regards >> Martin >> >> >> [0] https://patchwork.kernel.org/patch/10607157/#22238243 > > > . >