linux-kernel - Re: [PATCH 2/2] arm64: dts: rockchip: add eMMC's power domain support for rk3399

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Date:   Thu, 1 Sep 2016 14:56:46 +0800
From:   Ziyuan Xu <xzy.xu@...k-chips.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Shawn Lin <shawn.lin@...k-chips.com>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Heiko Stübner <heiko@...ech.de>,
        Xing Zheng <zhengxing@...k-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Frank Wang <frank.wang@...k-chips.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Elaine Zhang <zhangqing@...k-chips.com>,
        Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Norris <briannorris@...omium.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>,
        David Wu <david.wu@...k-chips.com>,
        Caesar Wang <wxt@...k-chips.com>,
        Jianqun Xu <jay.xu@...k-chips.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Shunqian Zheng <zhengsq@...k-chips.com>
Subject: Re: [PATCH 2/2] arm64: dts: rockchip: add eMMC's power domain support
 for rk3399

Hi


On 2016年09月01日 12:20, Doug Anderson wrote:
> Hi,
>
> On Wed, Aug 31, 2016 at 7:29 PM, Ziyuan Xu <xzy.xu@...k-chips.com> wrote:
>>> This is fine to pick up _only_ if you don't care about suspend/resume.
>>> If you care about suspend/resume then someone needs to first write a
>>> patch that will re-init all "corecfg" values after power is turned on.
>>
>> Do you mean corecfg_clockmultiplier and corecfg_baseclkfreq, if yes, we
>> don't need to strore/re-init it after resume.
>> corecfg_clockmultiplier is only used to fetch host->clk_mul, and
>> host->clk_mul has been a fixed value at run-time, unless driver unbind.
>> The same as corecfg_clockmultiplier, corecfg_baseclkfreq is used to check
>> the xin_clk at probe time, we don't reference it at run-time.
>> BTW, I have tested suspend/resume on rk3399 prior to this sumbit, eMMC works
>> fine.
> I guess I don't actually know how the corecfg_clockmultiplier and
> corecfg_baseclkfreq fields are actually used, but I presume that they
> actually do something useful and aren't used to just communicate back
> to software?

Take corecfg_clockmultiplier as example.
1. sdhci driver fetch host->clk_mul from corecfg_clockmultiplier
2. mmc->f_min and mmc->f_max are calculated via host->clk_mul, they're 
used for further initialization.
3. if the corecfg_clockmultiplier is incorrect, sdhci will use improper 
frequency to play.

I think we don't need to store it due to it's a fixed value at run-time, 
even if it is reset after a power cycle, the above will not be changed 
via software, except for dirver unbind .

>
> I know that:
>
> 1. If I don't pick this patch and I suspend/resume,
> corecfg_clockmultiplier and corecfg_baseclkfreq are still fine after
> suspend / resume.
>
> 2. If I do pick this patch and I suspend/resume,
> corecfg_clockmultiplier and corecfg_baseclkfreq are wrong after
> suspend/resume (tested by reading /dev/mem directly from userspace
> after suspend/resume).
>
>
> Are you saying that it is unimportant that corecfg_clockmultiplier and
> corecfg_baseclkfreq are wrong?

Yup, corecfg_* stuff will be reset after a power cycle.
I mean that we need only to guarantee they're correct at probe time.

>
>>> Technically I think this should probably use "pm runtime" and not
>>> normal suspend/resume hooks.  Any time we end up pm runtime suspended
>>> then I think our power will go off (because of genpd?) and we need to
>>> restore values.
>>
>> I understand your consideration. BUT genpd is in charge of on/off pd if the
>> corresponding device node has "power-domains" property. RPM is unnecessary
>> for this situation, we will not use autosuspend, right?
>>
>> @shawn, what's your opinion?
> I haven't dug.  If Runtime PM isn't enabled for sdhci-of-arasan then I
> guess we can just worry about suspend/resume, though.
>
> -Doug
>
>
>