Re: [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@xxxxxxxxxxxxxx> 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?