Date:	Tue, 18 Nov 2014 14:54:54 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Olliver Schinagl <oliver@...inagl.nl>
Cc:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Simon <longsleep@...il.com>, linux-pwm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv9 0/2] Add Allwinner SoCs PWM support

On Tue, Nov 18, 2014 at 02:47:33PM +0100, Olliver Schinagl wrote:
> Hey Alexandre,
> 
> On 05-11-14 16:15, Alexandre Belloni wrote:
> >Hi,
> >
> >This patch series adds support for the PWM controller found on the Allwinner
> >SoCs.
> >
> >The first patch adds the driver itself.
> >The second patch adds the DT binding documentation
> >
> >Changes in v8:
> >  - renamed the driver sun4i as the PWM IP is different in the next sunxi SoCs
> Why did you decide to rename it to sun4i? From your bindings document I
> understand you still support sun4i and sun7i, what happened to sun5i?
> 
> I went over the datasheets of sun4i, sun5i and sun7i and the disp_lcd.c from
> the latest linux-sunxi kernels and have to agree, they are all 4
> inconsistent and messy, but I'm not sure what you mean with PWM IP is
> different in next sunxi soc's. is sun5i different to sun4i? is sun7i
> different? or is sun6i (A31), sun8i (a80) and sun9i (A23) different?
> 
> What I get from the datasheet is, that sun4i and sun5i are exactly the same,
> with the exception that sun5i only has 1 PWM (~exposed~). I belive that is
> easily solved with the bindings by having allwinner-sun4i and allwinner
> sun5i bindings if I'm not mistaken.
> 
> As for sun7i compared to the other ones, according to disp_lcd.c sun5i and
> sun7i should behave exactly the same. This is contradicting to the
> datasheet, where sun4i and sun5i are the same.
> 
> So what are the major differences that I can see between the 3? sun4i
> defines the PWM prescaler register value 0b1111 as being undefined, and
> sun5i and sun7i as /1? Did you verify this (I haven't I admit, i bumped into
> this while looking for your patch ;-) )? I wouldn't be supprised if it where
> a typo on allwinners end in the datasheet ... disp_lcd.c stops at 72000 for
> the last entry. We should just check sun4i, sun5i and sun7i hardware to see
> if it behaves the same with a prescaler of 0b1111, which I would not be
> totally surprised if it did.
> 
> The other difference I notice is that sun7i and sun5i use 16bit period
> register where sun4i uses a 8bit register. This is probably the only reason
> why they put a #ifdef in disp_lcd.c, calculations turn out differently. I
> don't recognize this behavior at all in your driver however. I do think they
> that there is a difference here, since they did split up the original driver
> here because of this difference.
> 
> The pre-scaler bypass bit and pwm ready bit you all ready take care of :)

A31 and later are using a different IP, that is not supported by this
driver.

This driver only support the controller introduced with the A10, that
only saw minor differences between SoCs, like you have shown.

> Finally, though I'm sure I should have replied to it inline in the actual
> code, but hoping i can let it slip through here is that you define your
> local data as:
> 
> + static const struct sun4i_pwm_data sun4i_pwm_data_a20 = {
> 
> which looks really strange to me, since there is no a20 using the sun4i
> architecture :) I know it's just nitpicking, it just looks really odd. Maybe
> the compatible naming works just as well? sun4i_pwm_data; sun7i_pwm_data
> (and sun5i_pwm_data if you want to take care of only pwm0, only pwm1 (if we
> ever encounter such a configuration, disabled pwm0, enabled pwm1) or both to
> be used?)

This driver is name sun4i_pwm, hence the prefix.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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