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

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Date:   Wed, 21 Dec 2016 19:07:00 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        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 12/21/16 5:05 PM, Stephen Boyd wrote:
> On 12/19, Pierre-Louis Bossart wrote:
>> 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.
>
> Ok, by clkdev design if a device is passed but there isn't a
> match in the lookup table it allows it to match based solely on
> the connection id. Given that the connection id is globally
> unique this will work.
>
> Hopefully we don't have two of these devices with pmc_plt_clk_<n>
> signals in a single system though. Then having the device name
> would help differentiate between the two. And then it may make
> sense to have some sort of ACPI lookup system, similar to how we
> have lookups for clks in DT.

So in short we keep the existing solution for now and will only use the 
device name if and when the pmc_plt_clk_<n> identifier is no longer 
unique due to hardware changes. Did I get this right?