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

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Date:   Wed, 9 Sep 2020 10:05:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Amit Kucheria <amitk@...nel.org>
Cc:     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>,
        Taniya Das <tdas@...eaurora.org>
Subject: Re: [PATCH 5/7] cpufreq: qcom-hw: Use regmap for accessing hardware
 registers

On 08-09-20, 17:38, Amit Kucheria wrote:
> On Tue, Sep 8, 2020 at 5:18 PM Amit Kucheria <amitk@...nel.org> 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.

Right and I agree that is another useful aspect of it which I missed
mentioning.

> > > > 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.
> 
> Having said this, perhaps this patch can be held back for now, since
> we're not yet using some of the features of regmap to abstract away
> bit fields and such.
> 
> We don't strictly need it for just different register offsets.

Right, I just didn't understood why it was required currently as it
wasn't all that complex at all.

-- 
viresh