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

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Date:   Tue, 8 Sep 2020 16:58:28 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     rjw@...ysocki.net, robh+dt@...nel.org, agross@...nel.org,
        bjorn.andersson@...aro.org, amitk@...nel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dmitry.baryshkov@...aro.org, tdas@...eaurora.org
Subject: Re: [PATCH 5/7] cpufreq: qcom-hw: Use regmap for accessing hardware
 registers

On 0908, Viresh Kumar 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.
> 
> > Moreover it handles the proper locking for us in the core (spinlock vs mutex).
> 
> What locking do you need here ?
> 

I was just referring the case where if we need the locking in future, regmap
handles it nicely in the core.

> > I've seen many subsystem maintainers prefer regmap over plain readl/writel
> > calls. I'll add the reason in commit log.
> 
> I am not sure if it is worth it here.
> 

Hmm, I thought it is recommended to use regmap for MMIO access as well. I can
drop the patch if you want but let's wait for Bjorn/Amit to get their views.

Thanks,
Mani

> -- 
> viresh