Re: [PATCH v4 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ FW bindings

[Taniya Das]

On 6/18/2018 2:51 PM, Sudeep Holla wrote:
> On 15/06/18 18:40, Taniya Das wrote:
> > On 6/15/2018 5:29 PM, Amit Kucheria wrote:
>
> [...]
>
> > > A future version of the HW engine, or more likely, a firmware
> > > revision, will make more functionality available. Say, this needs
> > > access to another register or two. This will require changing the DT
> > > bindings. Instead, if you map the entire address space, you can just
> > > add offsets to the new registers.
> > >
> > > So in this case, I think you should define the following addresses
> > > (size 0x1400) for the two frequency domains
> > >
> > > 0x17d43000, 0x1400 (power cluster)
> > > 0x17d45800, 0x1400 (perf cluster)
> > >
> > > And in the driver simply add offsets as follows:
> > >
> > > #define ENABLE_OFFSETÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 0x0
> > > #define LUT_OFFSETÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 0x110
> > > #define PERF_DESIRED_OFFSET 0x920
> >
> > The offsets could vary across versions of this IP and that is the reason
> > to provide them through the DT and not define any such offsets.
>
> Just get compatibles to identify the version of the hardware if it can't
> be probed and detected. Please don't use DT to get the addresses of each
> register you use in the driver. That's neither scalable nor nice
> solution to the problem.
> Hello Sudeep and Amit,

Thanks for the comments, I am consolidating the understanding from the 
other emails in a single one.

I understand that you are looking for this IP to map the full region and 
define offsets according to access them.

But I still not sure how do you want this common driver to scale in the 
cases where the offsets could vary across version change.

 DT
====
  freq-node {
	reg = < X x_size>;   Where X is the start of the IP address.
  }

Driver code (The below representation is just for example).
=============

V1
#define ENABLE	0x0
#define LUT_V1	0x110
#define PERF_V1	0x920

V2
#define LUT_V2	0x150
#define PERF_V2	0x980

V3
#define LUT_V3	0x120
....

Do you want me to use "compatible" flag to

if (compatible == v1)
 enable =  readl_relaxed(X + LUT_V1);
else if (compatible == v2)
 enable = readl_relaxed(X + LUT_V2);
else if (compatible == v3)
 enable = readl_relaxed(X + LUT_V2);

With the current design I do not need such compatible checks and unmap 
the ones which are not required after probe. Please let me know your 
comments.

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