linux-kernel - Re: [alsa-devel] [PATCH v6 1/3] clk: x86: Add Atom PMC platform clocks

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Message-ID: <7f3d03dc-24fe-ec3f-4a3b-926c28f0ac86@linux.intel.com>
Date:   Mon, 19 Dec 2016 10:11:49 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Stephen Boyd <sboyd@...eaurora.org>
Cc:     ALSA Development Mailing List <alsa-devel@...a-project.org>,
        linux-clk@...r.kernel.org, Irina Tirdea <irina.tirdea@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Brown <broonie@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Takashi Iwai <tiwai@...e.com>,
        platform-driver-x86@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Len Brown <lenb@...nel.org>
Subject: Re: [alsa-devel] [PATCH v6 1/3] clk: x86: Add Atom PMC platform
 clocks

On 12/17/16 7:57 AM, Andy Shevchenko wrote:
> On Sat, Dec 17, 2016 at 3:33 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> On 12/15, Pierre-Louis Bossart wrote:
>
>>> Clients use devm_clk_get() with a "pmc_plt_clk_<n>"
>>> argument.
>>
>> This is the problem. Clients should be calling clk_get() like:
>>
>>         clk_get(dev, "signal name in datasheet")
>>
>> where the first argument is the device and the second argument is
>> some string that is meaningful to the device, not the system as a
>> whole. The way clkdev is intended is so that the dev argument's
>> dev_name() is combined with the con_id that matches some signale
>> name in the datasheet. This way when the same IP is put into some
>> other chip, the globally unique name doesn't need to change, just
>> the device name that's registered with the lookup. Obviously this
>> breaks down quite badly when dev_name() isn't stable. Is that
>> happening here?
>
> PMC Atom is a PCI device and thus each platform would have different
> dev_name(). Do you want to list all in each consumer if consumer wants
> to work on all of them or I missed something?
>
> So, the question is how clock getting will look like to work on
> currently both CherryTrail and BayTrail.

The name pmc_plt_clk_<n> follows the data sheet specification, where 
this convention is suggested:
   PLT_CLK[2:0] - Camera
   PLT_CLK[3] - Audio Codec
   PLT_CLK[4] -
   PLT_CLK[5] - COMMs

These clocks are not internal but are made available to external 
components through dedicated physical pins on the package, this external 
visibility limits the scope for confusions, variations. I have not seen 
any skews where these clocks and pins were changed at all.