linux-kernel - Re: [PATCH v3 2/5] ARM: OMAP2+: DRA7: Add hwmod entries for PWMSS

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Date:	Fri, 4 Mar 2016 06:25:50 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	"Franklin S Cooper Jr." <fcooper@...com>
cc:	Tony Lindgren <tony@...mide.com>, t-kristo@...com, vigneshr@...com,
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v3 2/5] ARM: OMAP2+: DRA7: Add hwmod entries for PWMSS

On Thu, 3 Mar 2016, Franklin S Cooper Jr. wrote:

> So I looked into this more and verified that the eCAP and
> ePWM doesn't have their own unique clock. The PWMSS receives
> a clock L4PER2_L3_GICLK/2 which is passed through to its
> sub-devices (ePWM, eCAP and eQEP). The PWMSS is responsible
> for handling its clock internally while the subdevices have
> no role in managing this clock. So this explains why we have
> hwmod entries for PWMSS and why we are planning on removing
> it from the various subdevices.

It's not whether they have their own unique clock, but whether the 
submodules have OCP integration registers, speak the idle/standby 
protocols, have direct L3/L4 ports, etc.

> Since ePWM, eCAP and eQEP are subdevices of PWMSS they
> shouldn't have their own concept of their "own" clock. The
> ePWM , eCAP and eQEP clocks are all shared and managed by
> their parent PWMSS. Once the PWMSS is enabled and has its
> clock running then ePWM, eCAP and eQEP from their main clock
> perspective have everything they need.
> 
> So my plan is to strip all references of clocks (including
> hwmod entries) for ePWM, eCAP and eQEP. The devm_clk_get
> calls made in the ePWM and eCAP will simply point to their
> parent's dev (PWMSS). I did a couple of quick test using
> this approach and it works. I have more testing to do but if
> that checks out are you ok with the above approach?

I don't know if that should be done or not.  I haven't stared at the code 
yet, but based on your description, it sounds to me that it probably 
shouldn't be done.  In any case, it's not what I meant...

> Also I'm not sure how simple-bus fits in this picture. The
> eCAP, eQEP and ePWM are all separate devices. The only thing
> that they share is a single clock from their parent. So it
> doesn't seem like the right approach. I'm basing this on the
> info in this thread
> https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg27979.html
> that talks about the usage of simple-bus. So if its outdated
> or I"m misinterpreting it incorrectly please let me know.

What I meant is that the ECAP*, EQEP*, EHRPWM* devices don't need to be 
registered through the hwmod code, due to the fact that they don't have 
the integration mentioned above.  Instead, I think those three subdevices 
should be listed as child nodes of epwmss* in the DT.

Looking at the DT data from Vignesh, it looks like he's already got 
ehrpwm1 as a child node of the epwmss1:

+               epwmss1: epwmss@...40000 {
+                       compatible = "ti,dra7xx-pwmss", "ti,am33xx-pwmss";
+                       reg = <0x48440000 0x30>;
+                       ti,hwmods = "epwmss1";
+                       #address-cells = <1>;
+                       #size-cells = <1>;
+                       status = "disabled";
+                       ranges = <0x48440100  0x48440100  0x80   /* ECAP */
+                                 0x48440180  0x48440180  0x80   /* EQEP */
+                                 0x48440200  0x48440200  0x80>; /* EHRPWM */
+
+                       ehrpwm1: ehrpwm@...40200 {
+                               compatible = "ti,dra7xx-ehrpwm",
+                                            "ti,am33xx-ehrpwm";
+                               #pwm-cells = <3>;
+                               reg = <0x48440200 0x80>;
+                               ti,hwmods = "ehrpwm1";

So, drop the above line, since the subdevices don't have corresponding 
hwmods any more.

+                               status = "disabled";
+                       };

Then, here, you'd add nodes similar to ehrpwm1 for ecap1 and eqep1.  I 
can't remember at the moment if adding "simple-bus" to the epwmss1 string 
would be sufficient to register the subdevices after the epwmss1 is 
probed.  If so, maybe that's all you need.

+               };

Then repeat for epwmss0, epwmss2.


- Paul