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

[Heiko Stübner]

Am Mittwoch, 20. August 2014, 09:27:02 schrieb Doug Anderson:
> Heiko,
> 
> On Wed, Aug 20, 2014 at 9:20 AM, Heiko Stübner <heiko@xxxxxxxxx> wrote:
> > Am Mittwoch, 20. August 2014, 08:55:09 schrieb Doug Anderson:
> >> Thierry,
> >> 
> >> On Wed, Aug 20, 2014 at 8:38 AM, Thierry Reding
> >> 
> >> <thierry.reding@xxxxxxxxx> wrote:
> >> > On Wed, Aug 20, 2014 at 08:20:53AM -0700, Doug Anderson wrote:
> >> >> Thierry,
> >> >> 
> >> >> On Tue, Aug 19, 2014 at 11:08 PM, Thierry Reding
> >> >> 
> >> >> <thierry.reding@xxxxxxxxx> wrote:
> >> >> > On Tue, Aug 19, 2014 at 08:18:54AM -0700, Doug Anderson wrote:
> >> >> >> Thierry,
> >> >> >> 
> >> >> >> On Tue, Aug 19, 2014 at 12:10 AM, Thierry Reding
> >> >> >> 
> >> >> >> <thierry.reding@xxxxxxxxx> wrote:
> >> >> >> > On Mon, Aug 18, 2014 at 10:09:06AM -0700, Doug Anderson wrote:
> >> >> >> >> The rk3288 SoC has an option to switch all of the PWMs in the
> >> >> >> >> system
> >> >> >> >> between the old IP block and the new IP block.  The new IP block
> >> >> >> >> is
> >> >> >> >> working and tested and the suggested PWM to use, so setup the
> >> >> >> >> SoC
> >> >> >> >> to
> >> >> >> >> use it and then we can pretend that the other IP block doesn't
> >> >> >> >> exist.
> >> >> > 
> >> >> > A few more questions as to how this actually works. Does it mean
> >> >> > there
> >> >> > are two physically separate blocks (with different physical
> >> >> > addresses)
> >> >> > to control the same PWM? And this register simply causes some of the
> >> >> > pins to be routed to one or another? As far as I recall there are a
> >> >> > number of instances of the PWM block, so the above would need to
> >> >> > count
> >> >> > for all of them. Or are there separate bits for each of them?
> >> >> 
> >> >> All I have is the TRM (technical reference manual) which doesn't give
> >> >> me much more info than I've provided you.  But I can answer some of
> >> >> your questoins:
> >> >> 
> >> >> 1. If there are two physically separate blocks then the "old" block is
> >> >> not documented in my TRM.
> >> >> 
> >> >> 1a) It's entirely possible it's located at some memory address that is
> >> >> marked "Reserved" in the TRM, but I have no idea.
> >> >> 
> >> >> 1b) It's entirely possible that the old IP block and the new IP block
> >> >> are supposed to be "compatible" but that the old block is broken and
> >> >> thus isn't behaving properly.
> >> >> 
> >> >> 1c) It's entirely possible that the old IP block and the new IP block
> >> >> are located at the same physical addresses but somehow work
> >> >> differently.  If so, the old IP block isn't documented.
> >> >> 
> >> >> 
> >> >> 2. As per the patch description, there is a single bit that controls
> >> >> all of the PWMs.  My guess is that there's actually a single IP block
> >> >> that implements all 4 PWMs.
> >> > 
> >> > 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@20030000 {
> >> >         
> >> >                 ...
> >> >                 reg = <0x20030000 0x10>;
> >> >                 ...
> >> >                 clocks = <&cru PCLK_PWM01>;
> >> >                 ...
> >> >         
> >> >         };
> >> >         
> >> >         pwm1: pwm@20030010 {
> >> >         
> >> >                 ...
> >> >                 reg = <0x20030010 0x10>;
> >> >                 ...
> >> >                 clocks = <&cru PCLK_PWM01>;
> >> >                 ...
> >> >         
> >> >         };
> >> >         
> >> >         ...
> >> >         
> >> >         pwm2: pwm@20050020 {
> >> >         
> >> >                 ...
> >> >                 reg = <0x20050020 0x10>;
> >> >                 ...
> >> >                 clocks = <&cru PCLK_PWM23>;
> >> >                 ...
> >> >         
> >> >         };
> >> >         
> >> >         pwm3: pwm@20050030 {
> >> >         
> >> >                 ...
> >> >                 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).
> > 
> > It did sound like a nice idea at the time to hold the common stuff of
> > rk3066/rk3188 and all their derivatives and I assumed a SoC that changed
> > dramatically (including the core) would be called 4xxx or so :-) .
> 
> Yes, I've fallen into the same trap.  Now I jump on the bandwagon and
> name things arbitrarily by the first machine that had them.  It's
> confusing, but sorta less confusing too.

the problem was in this case, that there also is rk3066-specific material which 
made it all the more difficult.

I guess rk3066-common would have been a possibility but still sounds somewhat 
strange, or something else entirely.

I'm not sure but don't think dtsi file-naming counts as API, so we can rename 
the rk3xxx.dtsi file if this gets to confusing in the future.


Heiko
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