Re: [PATCH v3 2/4] dt-bindings: nvmem: Add properties needed for blowing fuses

[Srinivas Kandagatla]

On 18/06/2020 18:25, Doug Anderson wrote:
> Hi,
>
> On Thu, Jun 18, 2020 at 9:55 AM Stephen Boyd <sboyd@xxxxxxxxxx> wrote:
> > Quoting Doug Anderson (2020-06-18 08:32:20)
> > > Hi,
> > >
> > > On Thu, Jun 18, 2020 at 7:01 AM Srinivas Kandagatla
> > > > On the other note:
> > > >
> > > > clock-names are not mandatory according to
> > > > Documentation/devicetree/bindings/clock/clock-bindings.txt
> > > >
> > > > For this particular case where clock-names = "sec" is totally used for
> > > > indexing and nothing else!
> > >
> > > So I guess in the one-clock case it's more optional and if you feel
> > > strongly I'll get rid of clk-names here.  ...but if we ever need
> > > another clock we probably will want to add it back and (I could be
> > > corrected) I believe it's convention to specify clk-names even with
> > > one clock.
> >
> > TL;DR: I suggest you call this "core" if you want to keep the
> > clock-name, or just drop it if there's only one clk and move on.
>
> Ah, true.  "core" sounds good.
>
>
> > It's not required to have clock-names with one clk, and indeed it's not
> > required to have clock-names at all. The multi clk scenario is a little
> > more difficult to handle because historically the clk_get() API has been
> > name based and not index based like platform resources. When there is
> > one clk the driver can pass NULL as the 'con_id' argument to clk_get()
> > and it will do the right thing. And when you have more than one clk you
> > can pass NULL still and get the first clk, that should be in the same
> > index, and then other clks by name.
> >
> > So far nobody has added clk_get_by_index() but I suppose if it was
> > important the API could be added. Working with only legacy clkdev
> > lookups would fail of course, but clock-names could be fully deprecated
> > and kernel images may be smaller because we're not storing piles of
> > strings and doing string comparisons. Given that it's been this way for
> > a long time and we have DT schema checking it doesn't seem very
> > important to mandate anything one way or the other though. I certainly
> > don't feel good when I see of_clk_*() APIs being used by platform
> > drivers, but sometimes it is required.
> >
> > To really put this into perspective, consider the fact that most drivers
> > have code that figures out what clk names to look for and then they pile
> > them into arrays and just turn them all on and off together. Providing
> > fine grained clk control here is a gigantic waste of time, and requiring
> > clock-names is just more hoops that driver authors feel they have to
> > jump through for $reasons. We have clk_bulk_get_all() for this, but that
> > doesn't solve the one rate changing clk among the sea of clk gates
> > problem. In general, driver authors don't care and we should probably be
> > providing a richer while simpler API to them that manages power state of
> > some handful of clks, regulators, and power domains for a device while
> > also letting them control various knobs like clk rate when necessary.
> >
> > BTW, on qcom platforms they usually name clks "core" and "iface" for the
> > core clk and the interface clk used to access the registers of a device.
> > Sometimes there are esoteric ones like "axi". In theory this cuts down
> > on the number of strings the kernel keeps around but I like that it
> > helps provide continuity across drivers and DTs for their SoCs. If you
> > ask the hardware engineer what the clk name is for the hardware block
> > they'll tell you the globally unique clk name like
> > "gcc_qupv3_uart9_core_clk", which is the worst name to use.
>
> OK, sounds about what I expected.  I suppose the path of least
> resistance would be to just drop clock-names.  I guess I'm just
> worried that down the road someone will want to specify the "iface"
> clock too.  If that ever happens, we're stuck with these options:
>
> 1. Be the first ones to require adding clk_get_by_index().
>
> 2. Use the frowned upon of_clk_get() API which allows getting by index.
>
> 3. Get the first clock with clk_get(NULL) and the second clock with
> clk_get("iface") and figure out how to specify this happily in the
> yaml.
>
> If we just define clock-names now then we pretty much match the
> pattern of everyone else.

Thanks to Stephen Boyd for his inputs and directions here!

I guess we have to live with "clock-names" for now for both consistency 
and reasons detailed by Boyd.

Am okay with the clock-names!

--srini
> Srinivas: reading all that if you still want me to drop clock-names
> then I will.  I'll use clk_get(NULL) to get the clock and if/when we
> ever need an "iface" clock (maybe we never will?) we can figure it out
> then.
>
>
> -Doug