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

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Date:   Fri, 15 Jun 2018 14:27:15 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Amit Kucheria <amit.kucheria@...durent.com>,
        Taniya Das <tdas@...eaurora.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Saravana Kannan <skannan@...eaurora.org>
Subject: Re: [PATCH v4 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ FW
 bindings



On 15/06/18 12:59, Amit Kucheria wrote:
> On Thu, Jun 14, 2018 at 9:24 PM, Taniya Das <tdas@...eaurora.org> wrote:
> 

[...]

>>
>> Yes I do understand the intent of mapping the whole register space, but as
>> per the HW specs these 3 registers would be the only ones required for now.
>> I do not think this hardware engine has any information on the power
>> numbers.
> 
> "For now" - I think this is exactly the point that Sudeep is trying to make.
> 
> 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_OFFSET               0x0
> #define LUT_OFFSET                      0x110
> #define PERF_DESIRED_OFFSET 0x920
> 
> This will allow you add any new registers in the future w/o modifying
> the DT binding and reduce qcom_cpu_resources_init() to a handful of
> lines since you no longer need so many OF string matches, and
> devm_ioremap()s.
> 

Thanks Amit for such nice and detailed explanation. I was lazy to write
in such details, but was hoping Taniya to understand the point. Anyways
thanks again for doing this.

-- 
Regards,
Sudeep