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

[Doug Anderson]

Hi,

On Wed, Aug 31, 2016 at 11:56 PM, Ziyuan Xu <xzy.xu@xxxxxxxxxxxxxx> wrote:
> Hi
>
>
> On 2016å09æ01æ 12:20, Doug Anderson wrote:
>>
>> Hi,
>>
>> On Wed, Aug 31, 2016 at 7:29 PM, Ziyuan Xu <xzy.xu@xxxxxxxxxxxxxx> 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.

So are you saying that the entire purpose of "corecfg_clockmultiplier"
is that causes the "ClockMultiplier" field of the "EMMCCORE_CAP"
register to get a certain value?
...and that the entire purpose of "corecfg_baseclkfreq" is that it
causes the "BaseClockFreqSDClock" field of the "EMMCCORE_CAP" register
to get a certain value?

That would have been nice to know before.  I had assumed that those
"corecfg" settings did something else more useful.

If it is indeed true that these corecfg values are as silly as it
seems, then I guess it's not terribly important to re-set them after
suspend/resume.  Eventually it would be nice/clean to actually do so
(in case the SDHCI driver eventually changes), but I guess we wouldn't
need to block. this patch from landing.

Can you please confirm my understanding above?


-Doug