Re: [PATCH 04/11] mmc: sdhci-of-arasan: Properly set corecfg_baseclkfreq on rk3399

From: Shawn Lin <shawn.lin@rock-chips.com>
To: Doug Anderson <dianders@chromium.org>
Cc: shawn.lin@rock-chips.com, Ulf Hansson <ulf.hansson@linaro.org>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Rob Herring <robh+dt@kernel.org>,
	Ziyuan Xu <xzy.xu@rock-chips.com>,
	Brian Norris <briannorris@chromium.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Michal Simek <michal.simek@xilinx.com>,
	soren.brinkmann@xilinx.com,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 04/11] mmc: sdhci-of-arasan: Properly set corecfg_baseclkfreq on rk3399
Date: Tue, 14 Jun 2016 08:59:15 +0800	[thread overview]
Message-ID: <da1c9ae9-71d9-6e9d-7b9f-08485ee9178e@rock-chips.com> (raw)
In-Reply-To: <CAD=FV=UL5tU8RWtHF=-pE8SA0jUcBsqQDOU0BrruXOF7yGh5xg@mail.gmail.com>

在 2016/6/14 8:43, Doug Anderson 写道:
> Hi,
>
> On Mon, Jun 13, 2016 at 5:14 PM, Shawn Lin <shawn.lin@rock-chips.com> wrote:
>>>> It's broken when reading capabilities reg on RK3399 platform
>>>> which means you should get it via clk framework. But you should consider
>>>> the non-broken case.
>>>
>>>
>>> I'm afraid I don't understand.  Can you elaborate?  Are you saying if
>>> things weren't broken then we wouldn't have to ask the common clock
>>> framework for this?  Where would we get this value?
>>
>>
>>
>> I mean bascially we should get baseclk from capabilities register[15:8]
>> (offset 0x40@sdhci), namely EMMCCORE_CAP on TRM. Only when you get 0x0
>> from there, can you consider to get it from clock framework.
>
> Ah, got it!
>
> I guess I would be super surprised if an SoC implemented
> register[15:8] but still then required you to manually copy that value
> to corecfg_baseclkfreq.  Presumably nobody would be crazy enough to
> try to measure the clock rate in the SDHCI driver, so this would
> probably only be non-zero where the SDHCI clock is totally fixed.
> ...in that case probably the SoC designer would also put a default
> value in corecfg_baseclkfreq that matched (and maybe even make
> corecfg_baseclkfreq read-only?).

yes, you could see some others similar capabilities case like
timeoutclkfreq or preset value, etc. SDHCI hope Soc designer to
implement them within the controller but not mandatory.

>
> Even in the case that an SoC designer didn't put a value into
> corecfg_baseclkfreq that matched register[15:8], it seems very likely
> that the rate returned from the clk_get_rate() would match.
>
> I guess what I'm saying is that, to me, it seems like my patch isn't
> broken in any real systems.  If we ever find a system that needs this
> behavior in the future, we can add it.  Until then, it seems like my
> patch would be fine.  Do you agree?

I agree. But from the code itself, we should still use
SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN to see if we could get
it from internal register in case of some platforms don't
provide the clk stuff.. Sounds sane? :)

>
> Note: right now we only provide a register map for rk3399, so
> certainly we can't be breaking any other SoCs with our current method.
>
>
>> I don't see a reason to check the return code here.  Specifically:
>>>
>>> * If this is a SoC where you don't need to write corecfg_baseclkfreq
>>> then we need do nothing about this error.
>>>
>>> * If the regmap write failed (which would be terribly unexpected for a
>>> memory mapped register) then we've already printed an error (in
>>> sdhci_arasan_syscon_write).  Best course of action seems to keep going
>>> and try anyway.
>>>
>>>
>>> I don't think a retry is likely to help anything.
>>
>>
>> Well, I saw you add a return value for sdhci_arasan_syscon_write, so
>> should we remove it?
>
> It was presuming that there might be future callers who might want to
> write other corecfg registers and might need to know whether the write
> worked or not.  Since having the return value doesn't hurt anything
> I'd rather leave it in.  If you really want me to remove it, though, I
> will.  Just let me know.

Ahh, it's trivial, so keep it if you want.

>
>
> -Doug
>
>
>

-- 
Best Regards
Shawn Lin