Date: Mon, 18 Dec 2017 14:13:29 +0530
From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, huntbag@linux.vnet.ibm.com,
        Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        linux-pm@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [v3 PATCH 3/3] powernv-cpufreq: Treat pstates as opaque 8-bit
 values
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Hi Balbir,

On Sun, Dec 17, 2017 at 02:17:02PM +1100, Balbir Singh wrote:
> On Wed, Dec 13, 2017 at 5:57 PM, Gautham R. Shenoy
[..snip..]
> >
> > -static inline int extract_pstate(u64 pmsr_val, unsigned int shift)
> > +static inline u8 extract_pstate(u64 pmsr_val, unsigned int shift)
> >  {
> > -       int ret = ((pmsr_val >> shift) & 0xFF);
> > -
> > -       if (!ret)
> > -               return ret;
> > -
> > -       return (pstate_sign_prefix | ret);
> > +       return ((pmsr_val >> shift) & 0xFF);
> >  }
> 
> So we just added this and moved from an int to u8. I was going to ask
> if we still need an int in patch1, but I thought the driver dealt with
> just integers because of the larger framework.

The larger framework is with respect to the device tree which defines
pstates as 32-bit integers (I am not aware of the reasons for this
choice, but perhaps device-tree doesn't have a s8/u8 type?!). The
driver still knows that pstates are only 8-bits wide because of the
PMSR,PMCR definitions. Before this patch, the driver was still doing
the conversions from 8-bit to int and vice-versa every time. With this
patch, we do it only once, i.e at the initialization. After that we
treat pstates as 8-bit integers. 


> 
> Balbir Singh.
>