linux-kernel - Re: [PATCH 1/4] ARM: rockchip: rk3288: Switch to use the proper PWM IP

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Date:	Thu, 21 Aug 2014 08:39:43 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Caesar Wang <caesar.wang@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Olof Johansson <olof@...om.net>,
	Eddie Cai <eddie.cai@...k-chips.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] ARM: rockchip: rk3288: Switch to use the proper PWM IP

Thierry and Heiko

On Wed, Aug 20, 2014 at 11:24 PM, Thierry Reding
<thierry.reding@...il.com> wrote:
> On Wed, Aug 20, 2014 at 08:55:09AM -0700, Doug Anderson wrote:
>> On Wed, Aug 20, 2014 at 8:38 AM, Thierry Reding <thierry.reding@...il.com> wrote:
> [...]
>> > Looking at the register offsets in the device tree that seems likely. At
>> > least PWMs 0 and 1 as well as 2 and 3 seem like they could be in the
>> > same IP block. Their placement in the register map is somewhat strange:
>> >
>> >         pwm0: pwm@...30000 {
>> >                 ...
>> >                 reg = <0x20030000 0x10>;
>> >                 ...
>> >                 clocks = <&cru PCLK_PWM01>;
>> >                 ...
>> >         };
>> >
>> >         pwm1: pwm@...30010 {
>> >                 ...
>> >                 reg = <0x20030010 0x10>;
>> >                 ...
>> >                 clocks = <&cru PCLK_PWM01>;
>> >                 ...
>> >         };
>> >
>> >         ...
>> >
>> >         pwm2: pwm@...50020 {
>> >                 ...
>> >                 reg = <0x20050020 0x10>;
>> >                 ...
>> >                 clocks = <&cru PCLK_PWM23>;
>> >                 ...
>> >         };
>> >
>> >         pwm3: pwm@...50030 {
>> >                 ...
>> >                 reg = <0x20050030 0x10>;
>> >                 ...
>> >                 clocks = <&cru PCLK_PWM23>;
>> >                 ...
>> >         };
>>
>> Ah, you're looking at "rk3xxx.dtsi".  That doesn't apply to rk3288
>> (the downsides of trying to guess ahead of time what SoC vendors will
>> name new models).
>>
>> In rk3288 they have the same clocks.  See patch #3 in this series.
>>
>>
>> > The clocks would also indicate that there are actually two blocks. I
>> > seem to remember a discussion about whether to handle them as a single
>> > block or two/four, but I can't seem to find a reference to it. Maybe I'm
>> > confusing it with another driver.
>>
>> At this point it seems like the choice has already been made to handle
>> them as separate PWMs.  I can change this choice if you want...
>
> Well, looking at patch 3/4 this really does seem to be one single block
> providing four PWM channels, so the right thing to do would be to
> represent it in one device tree node. But I'll leave it up to Heiko to
> decide how he wants to handle this.
>
> One downside of describing it as one device is that it would make the
> pinmux handling slightly more difficult, since presumably you'd only
> want to apply the pinmux settings when a channel is actually being used.
> Currently the pinmux doesn't apply as long as the device remains
> disabled in device tree (though enabling it doesn't necessarily mean
> that it's being used).
>
> Like I said, it's up to Heiko to decide whether it's worth making this
> change (and it'd make sense to apply it to existing DTS files
> retroactively) or better to keep what we have.

Please let me know if you'd like me to spin.  Otherwise I'll assume
this is OK as is.

-Doug
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