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

From: Doug Anderson <dianders@chromium.org>
To: Shawn Lin <shawn.lin@rock-chips.com>
Cc: 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: Mon, 13 Jun 2016 19:13:43 -0700	[thread overview]
Message-ID: <CAD=FV=WGwiQqRNMSSX9OR6nAOwuu7CbULuz7BcNp-S=duqpLLQ@mail.gmail.com> (raw)
In-Reply-To: <da1c9ae9-71d9-6e9d-7b9f-08485ee9178e@rock-chips.com>

Shawn,

On Mon, Jun 13, 2016 at 5:59 PM, Shawn Lin <shawn.lin@rock-chips.com> wrote:
>> 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? :)

Could we wait until there exists a SoC that needs to provide
baseclkfreq in its sdhci_arasan_soc_ctl_map table and that needs this
value copied from register[15:8]?

AKA:

A) If you have a SoC where clk_get_rate() is right and software needs
to set baseclkfreq manualy, then you should include "baseclkfreq" in
your sdhci_arasan_soc_ctl_map table.  This is like rk3399.  Note that
if _both_ clk_get_rate() and register[15:8] are right, that's fine.
We can still use clk_get_rate() since it will be exactly the same as
register[15:8].

B) If you have a SoC that doesn't even expose corecfg_baseclkfreq to
software control, just don't include "baseclkfreq" in your
sdhci_arasan_soc_ctl_map table.  Easy.  This is how my patch treats
anyone using the current "generic" bindings, but you could easily just
specify an offset of "-1" for baseclkfreq if you didn't want to use
the generic bindings but couldn't control baseclkfreq.

C) If you have a SoC that provides a valid value in register[15:8] and
clk_get_rate() is wrong and software is required to copy the value
from register[15:8] to baseclkfreq, technically we should fix
clk_get_rate() anyway.  It's good when common clock framework provides
correct values.  NOTE: It seems very unlikely to me that
register[15:8] would be right AND that software would be required to
copy this value to baseclkfreq, but I suppose there are some pretty
crazy hardware designs out there.

D) If you have a SoC that provides a valid value in register[15:8] and
clk_get_rate() is wrong and can't be fixed (REALLY?) and software is
required to copy the value from register[15:8] to baseclkfreq, we will
need to add new code.  My assertion is that such a SoC doesn't exist
and is unlikely to ever exist, so I am hesitant to add extra code to
support this SoC.

With my patch, A) and B) are certainly handled.  I think C) is
unlikely to exist, but if it did exist then I'd say we should fix
clk_get_rate().  I think D) is VERY unlikely to exist.  If I'm shown
proof of D) existing, I'm happy to submit a patch for it.  Until we
see proof of D)'s existence, I don't think we should clutter the code
with support for it.

-Doug