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

[Pierre-Louis Bossart]

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 at codeaurora.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?