Re: [PATCH 4/7] dt-bindings: chosen: Add clocksource and clockevent selection

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Sudeep Holla <sudeep.holla@arm.com>
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Subject: Re: [PATCH 4/7] dt-bindings: chosen: Add clocksource and clockevent selection
Date: Tue, 10 Sep 2019 17:10:55 +0200	[thread overview]
Message-ID: <20190910151055.GX21254@piout.net> (raw)
In-Reply-To: <20190910150826.GA18308@e107533-lin.cambridge.arm.com>

On 10/09/2019 16:08:26+0100, Sudeep Holla wrote:
> On Tue, Sep 10, 2019 at 02:51:50PM +0000, Claudiu.Beznea@microchip.com wrote:
> > 
> > 
> > On 10.09.2019 17:32, Sudeep Holla wrote:
> > > External E-Mail
> > > 
> > > 
> > > On Tue, Sep 10, 2019 at 04:47:13PM +0300, Claudiu Beznea wrote:
> > >> From: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > >>
> > >> Some timer drivers may behave either as clocksource or clockevent
> > >> or both. Until now, in case of platforms with multiple hardware
> > >> resources of the same type, the drivers were chosing the first
> > >> registered hardware resource as clocksource/clockevent and the
> > >> next one as clockevent/clocksource. Other were using different
> > >> compatibles (one for each functionality, although its about the
> > >> same hardware). Add DT bindings to be able to choose the
> > >> functionality of a timer.
> > >>
> > > 
> > > Is the piece of hardware not capable of serving as both clocksource
> > > and clockevent or is it just the platform choice ?
> > 
> > In my case, the hardware is not capable of serving at the same time
> > a clocksource device and a clockevent device.
> > 
> > First, I published v1 for a hardware device having this behavior at
> > [1] requesting 1st probed hardware device to work as clocksource and
> > the 2nd one to work as clockevent. The discussion at [1] ended up with
> > the idea of having a mechanism to specify which hardware device behaves
> > as clocksource and which one behaves as clockevent.
> >
> 
> In that case, why can't we identify capability that with the compatibles
> for this timer IP ?
> 
> IOW, I don't like the proposal as it's hardware limitation.
> 

To be clear, bot timers are exactly the same but can't be clocksource
and clockevent at the same time. Why would we have different compatibles
for the exact same IP?

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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