Message-ID: <53de5f06-3ae4-0fdd-d930-aa04e74c0319@xilinx.com>
Date:   Thu, 24 Jun 2021 18:25:50 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Sean Anderson <sean.anderson@...o.com>,
        Michal Simek <michal.simek@...inx.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
CC:     <linux-pwm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Alvaro Gamez <alvaro.gamez@...ent.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>, <kernel@...gutronix.de>
Subject: Re: [PATCH v3 2/2] clocksource: Add support for Xilinx AXI Timer

Hi,

On 6/18/21 11:24 PM, Sean Anderson wrote:
> 
> 
> On 6/16/21 8:12 AM, Michal Simek wrote:
>> Hi Uwe,
>>
>> On 5/25/21 8:11 AM, Uwe Kleine-König wrote:
>>> Hello Sean, hello Michal,
>>>
>>> On Mon, May 24, 2021 at 09:00:51AM +0200, Michal Simek wrote:
>>>> On 5/20/21 10:13 PM, Sean Anderson wrote:
>>>>> On 5/19/21 3:24 AM, Michal Simek wrote:
>>>>>> On 5/18/21 12:15 AM, Sean Anderson wrote:
>>>>>>> This could be deprecated, but cannot be removed since existing
> device
>>>>>>> trees (e.g. qemu) have neither clocks nor clock-frequency
> properties.
>>>>>>
>>>>>> Rob: Do we have any obligation to keep properties for other projects?
>>>
>>> If a binding is in the wild and used to be documented, it has to stay.
>>>
>>>>>>>> 4. Make driver as module
>>>>>>>> 5. Do whatever changes you want before adding pwm support
>>>>>>>> 6. Extend DT binding doc for PWM support
>>>>>>>> 7. Add PWM support
>>>>>>>
>>>>>>> Frankly, I am inclined to just leave the microblaze timer as-is.
> The PWM
>>>>>>> driver is completely independent. I have already put too much
> effort into
>>>>>>> this driver, and I don't have the energy to continue working on the
>>>>>>> microblaze timer.
>>>>>>
>>>>>> I understand. I am actually using axi timer as pwm driver in one
> of my
>>>>>> project but never had time to upstream it because of couple of
> steps above.
>>>>>> We need to do it right based on steps listed above. If this is too
> much
>>>>>> work it will have to wait. I will NACK all attempts to add separate
>>>>>> driver for IP which we already support in the tree.
>>>>>
>>>>> 1. Many timers have separate clocksource and PWM drivers. E.g.
> samsung,
>>>>>     renesas TPU, etc. It is completely reasonable to keep separate
>>>>>     drivers for these purposes. There is no Linux requirement that
> each
>>>>>     device have only one driver, especially if it has multiple
> functions
>>>>>     or ways to be configured.
>>>>
>>>> It doesn't mean that it was done properly and correctly. Code
>>>> duplication is bad all the time.
>>>
>>> IMHO it's not so much about code duplication. Yes, code duplication is
>>> bad and should be prevented if possible. But it's more important to not
>>> introduce surprises. So I think it should be obvious from reading the
>>> device tree source which timer is used to provide the PWM. I don't care
>>> much if this is from an extra property (like xilinx,provide-pwm),
>>> overriding the compatible or some other explicit mechanism. IIUC in this
>>> suggested patch the selection is implicit and so this isn't so nice.
>>>
>>>>> 2. If you want to do work on a driver, I'm all for it. However, if you
>>>>>     have not yet submitted that work to the list, you should not gate
>>>>>     other work behind it. Saying that X feature must be gated behind Y
>>>>>     *even if X works completely independently of Y* is just stifling
>>>>>     development.
>>>>
>>>> I gave you guidance how I think this should be done. I am not gating
> you
>>>> from this work. Your patch is not working on Microblaze arch which is
>>>> what I maintain. And I don't want to go the route that we will have two
>>>> drivers for the same IP without integration. We were there in past and
>>>> it is just pain.
>>>> I am expecting that PWM guys will guide how this should be done
>>>> properly. I haven't heard any guidance on this yet.
>>>> Thierry/Uwe: Any comment?
>>>
>>> Not sure I can and want to provide guidance here. This is not Perl, but
>>> still TIMTOWTDI. If it was me who cared here, I'd look into the
>>> auxiliary bus (Documentation/driver-api/auxiliary_bus.rst) to check if
>>> it can help to solve this problem.
>>
>> I recently got patches for cadence TTC driver
>> (drivers/clocksource/timer-cadence-ttc.c) for PWM support too. It is the
>> second and very similar case. This driver is used on Zynq as clock
>> source and can be also use as PWM. I can't believe that there are no
>> other examples how to deal with these timers which are used for PWM
>> generation.
>>
> 
> The approach I took in v4 is that probe functions and driver callbacks
> live in drivers/timer and drivers/pwm, and common functions live in
> drivers/mfd (although I may move them to drivers/timer since Lee Jones
> doesn't like them there).
> 
> I would greatly appreciate if you could review v4. It has been on the
> list for three weeks now with no comments from either you or Uwe.

I will take a look at it next week.

Thanks,
Michal

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