RE: [PATCH 2/2] dt-bindings: arm: Document RZ/A2 SoC DT bindings

From: Chris Brandt <Chris.Brandt@renesas.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Simon Horman <horms@verge.net.au>,
	Magnus Damm <magnus.damm@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>
Subject: RE: [PATCH 2/2] dt-bindings: arm: Document RZ/A2 SoC DT bindings
Date: Thu, 12 Jul 2018 13:15:24 +0000	[thread overview]
Message-ID: <TY1PR01MB15621B11047F645DE25485E68A590@TY1PR01MB1562.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <CAMuHMdXuXJdvtmEu3WYVSgwd0xfCpQcWQeL+FA9vUMxiA7h=VQ@mail.gmail.com>

Hi Geert,

On Thursday, July 12, 2018, Geert Uytterhoeven wrote:
> > +  - RZ/A2 (R7S9210)
> > +    compatible = "renesas,r7s9210"
> 
> There seems to be a difference between the r7s92104x and the r7s92105x
> parts (with "x" just denoting a different packaging)?
> Do we need one more digit?

From an "architecture" standpoint all the hardware in the RZ/A2 
(R7S9210xx series) will be the same. So from a device driver standpoint, 
CONFIG_ARCH_R7S9210 would cover everything.

The rest of the numbers are just for package and number of HW channels.

Of course, sometimes when they make smaller packages, they also make 
smaller silicon to make it cheaper. But in that case, they just simply 
remove HW or the number of channels for the hardware. (you don't need as 
many peripherals if you don't have as many pins anymore). But, they never 
change the functionality of the hardware.

Take for example RZ/A1
 RZ/A1H  R7S72100x
 RZ/A1M  R7S72101x
 RZ/A1L  R7S72102x
 RZ/A1LU R7S72103x

These parts all had the same hardware, but different package options And
the "L" parts were cheaper because they reduced the die size by 
removing HW.
But the same drivers worked on all of them because the IP was all 
exactly the same.
So I would have suggested CONFIG_ARCH_R7S7210 for the RZ/A1 series. 
(well, until I found about the R-Car part that took the same part number in 
this series)

As for the r7s92104x vs r7s92105x, that is for a HW feature that will 
have nothing to do with Linux, so we can ignore that number.

But even if we did make a tiny cut-down version of the device, say a 
R7S92106x, all HW IP would be the same, just less of it. So in my mind, the
architecture (from a CONFIG_ARCH perspective) is still the same. Maybe 
just a different .dtsi.

What do you think?

Chris