linux-kernel - Re: [PATCH 5/7] cpufreq: qcom-hw: Use regmap for accessing hardware registers

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Date:   Tue, 8 Sep 2020 15:08:51 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Amit Kucheria <amitk@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Taniya Das <tdas@...eaurora.org>
Subject: Re: [PATCH 5/7] cpufreq: qcom-hw: Use regmap for accessing hardware
 registers

On Tue, Sep 08, 2020 at 05:18:35PM +0530, Amit Kucheria wrote:
> On Tue, Sep 8, 2020 at 4:48 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 08-09-20, 16:41, Manivannan Sadhasivam wrote:
> > > On 0908, Viresh Kumar wrote:
> > > > On 08-09-20, 13:27, Manivannan Sadhasivam wrote:
> > > > > Use regmap for accessing cpufreq registers in hardware.
> > > >
> > > > Why ? Please mention why a change is required in the log.
> > > >
> > >
> > > Only because it is recommended to use regmap for abstracting the hw access.
> >
> > Yes it can be very useful in abstracting the hw access in case of
> > busses like SPI/I2C, others, but in this case there is only one way of
> > doing it with the exact same registers. I am not sure it is worth it
> > here. FWIW, I have never played with regmaps personally, and so every
> > chance I can be wrong here.
> 
> One could handle the reg offsets through a struct initialisation, but
> then you end up with lots of #defines for bitmasks and bits for each
> version of the IP. And the core code becomes a bit convoluted IMO,
> trying to handle the differences.
> 
> regmap hides the differences of the bit positions and register offsets
> between several IP versions.
> 
> > > Moreover it handles the proper locking for us in the core (spinlock vs mutex).
> >
> > What locking do you need here ?
> 
> Right, locking isn't the main reason here.

If that is the case, IMO it is better to set disable_lock or something
in config especially as this regmap_write is used in qcom_cpufreq_hw_fast_switch

-- 
Regards,
Sudeep