On 10/16/18 3:04 PM, Thierry Reding wrote:

On Tue, Oct 16, 2018 at 10:31:42AM -0700, Paul Walmsley wrote:

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On 10/16/18 4:01 AM, Thierry Reding wrote:

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On Mon, Oct 15, 2018 at 03:57:35PM -0700, Atish Patra wrote:

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On 10/10/18 6:49 AM, Thierry Reding wrote:

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On Tue, Oct 09, 2018 at 11:51:22AM -0700, Atish Patra wrote:

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+Required properties:
+- compatible: should be one of
+	"sifive,fu540-c000-pwm0","sifive,pwm0".

What's the '0' in here? A version number?

I think yes. Since fu540 is the first Linux capable RISC-V core, SiFive Guys
decided mark it as version 0.

@Wesly: Please correct me if I am wrong.

It seems fairly superfluous to me to have a version number in additon to
the fu540-c000, which already seems to be the core plus some sort of
part number. Do you really expect there to be any changes in the SoC
that would require a different compatible string at this point? If the
SoC has taped out, how will you ever get a different version of the PWM
IP in it?

I would expect any improvements or changes to the PWM IP to show up in a
different SoC generation, at which point it would be something like
"sifive,fu640-c000" maybe, or perhaps "sifive,fu540-d000", or whatever
the numbering is.

The "0" suffix refers to a revision number for the underlying PWM IP block.

It's certainly important to keep that version number on the "sifive,pwm0"
compatible string that doesn't have the chip name associated with it.

Isn't the hardware identified by "sifive,pwm0" and "sifive,fu540-c000"
effectively identical? 

Yes.

Is there a need to have two compatible strings

that refer to the exact same hardware?

The DT in the hardware has only sifive,pwm0. I have added 
"sifive,fu540-c000" as that was concluded as the correct compatible 
string from platform level interrupt controller patch(PLIC) discussion.

(http://lists.infradead.org/pipermail/linux-riscv/2018-August/001135.html)

"sifive,pwm0" is required to until all the Unleashed SoC gets an updated 
firmware with correct compatible string "sifive,fu540-c000". I agree 
this is a mess. But we have to carry it until all every DT(corresponding 
to each driver) is finalized. I guess SiFive will release a firmware 
update that contains all the updated DT once that is done. We can get 
rid of all the redundant compatible strings at that time.

Regards,
Atish

quoted

As to whether there could ever be a FU540-C000 part with different IP block
versions on it: FU540-C000 is ultimately a marketing name.  While
theoretically we shouldn't have another "FU540-C000" chip with different
peripheral IP block versions on it, I don't think any engineer can guarantee
that it won't happen.

I would argue that if at some point there was indeed a chip with the
same name but a different IP block version in it, we can figure out what
to call it. Sure there are no guarantees, but it's still fairly unlikely
in my opinion, so I personally wouldn't worry about this up front.

Anyway, I don't feel strongly either way, I'm just pointing out that
this is somewhat unusual. If you want to keep it, feel free to.

Thierry