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Subject: Re: [PATCH v4 1/3] dt-bindings: pwm: Add Xilinx AXI Timer
To:     Sean Anderson <sean.anderson@seco.com>,
        Michal Simek <monstr@monstr.eu>, <linux-pwm@vger.kernel.org>,
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From:   Michal Simek <michal.simek@xilinx.com>
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Date:   Fri, 2 Jul 2021 14:40:56 +0200
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On 7/1/21 5:32 PM, Sean Anderson wrote:
> 
> 
> On 6/30/21 9:47 AM, Michal Simek wrote:
>>
>>
>> On 5/28/21 11:45 PM, Sean Anderson wrote:
>>> This adds a binding for the Xilinx LogiCORE IP AXI Timer. This device is
>>> a "soft" block, so it has many parameters which would not be
>>> configurable in most hardware. This binding is usually automatically
>>> generated by Xilinx's tools, so the names and values of some properties
>>> must be kept as they are. Replacement properties have been provided for
>>> new device trees.
>>>
>>> Because we need to init timer devices so early in boot, the easiest way
>>> to configure things is to use a device tree property. For the moment
>>> this is 'xlnx,pwm', but this could be extended/renamed/etc. in the
>>> future if these is a need for a generic property.
>>>
>>> Signed-off-by: Sean Anderson <sean.anderson@seco.com>
>>> ---
>>>
>>> Changes in v4:
>>> - Remove references to generate polarity so this can get merged
>>> - Predicate PWM driver on the presence of #pwm-cells
>>> - Make some properties optional for clocksource drivers
>>>
>>> Changes in v3:
>>> - Mark all boolean-as-int properties as deprecated
>>> - Add xlnx,pwm and xlnx,gen?-active-low properties.
>>> - Make newer replacement properties mutually-exclusive with what they
>>>   replace
>>> - Add an example with non-deprecated properties only.
>>>
>>> Changes in v2:
>>> - Use 32-bit addresses for example binding
>>>
>>>  .../bindings/pwm/xlnx,axi-timer.yaml          | 85 +++++++++++++++++++
>>>  1 file changed, 85 insertions(+)
>>>  create mode 100644
> Documentation/devicetree/bindings/pwm/xlnx,axi-timer.yaml
>>>
>>> diff --git
> a/Documentation/devicetree/bindings/pwm/xlnx,axi-timer.yaml
> b/Documentation/devicetree/bindings/pwm/xlnx,axi-timer.yaml
>>> new file mode 100644
>>> index 000000000000..48a280f96e63
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/pwm/xlnx,axi-timer.yaml
>>
>> I don't think this is the right location for this.
>>
>> I have done some grepping and I think this should be done in a different
>> way. I pretty much like solution around "ti,omap3430-timer" which is
>> calling dmtimer_systimer_select_best() and later dmtimer_is_preferred()
>> which in this case would allow us to get rid of cases which are not
>> suitable for clocksource and clockevent.
>>
>> And there is drivers/pwm/pwm-omap-dmtimer.c which has link to timer
>> which is providing functions for it's functionality.
>>
>> I have also looked at
>> Documentation/devicetree/bindings/timer/nxp,tpm-timer.yaml which is also
>> the same device.
> 
> Ok, I will move this under bindings/timer.
> 
>>
>> And sort of curious if you look at
>>
> https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v2_0/pg079-axi-timer.pdf
> 
>> ( Figure 1-1)
>> that PWM is taking input from generate out 0 and generate out 1 which is
>> maybe can be modeled is any output and pwm driver can register inputs
>> for pwm driver.
> 
> I don't think that is a good model, since several bits (GENERATE, PWM,
> etc) need to be set in the TCSR, and we need to coordinate changes
> between timers closely to keep our contract for apply_state(). Although
> that is how the hardware is organized, the requirements of the
> clocksource and pwm subsystems are very different.

There is another upstream solution done by samsung. Where they use
samsung,pwm-outputs property to identify PWMs. I think that make sense
to consider to identify which timer should be clocksource/clockevent
because with MB SMP this has to be done to pair timer with cpu for
clockevents.

You can see drivers here.
drivers/clocksource/smasung_pwm_timer.c
drivers/pwm/pwm-samsung.c

Uwe: How does it sound to you?

Thanks,
Michal