From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "ego@linux.vnet.ibm.com" <ego@linux.vnet.ibm.com>,
Linux PM list <linux-pm@vger.kernel.org>,
linuxppc-dev@ozlabs.org
Subject: Re: [PATCH v3 5/5] powernv:cpufreq: Implement the driver->get() method
Date: Fri, 21 Mar 2014 18:34:51 +0530 [thread overview]
Message-ID: <20140321130450.GD2493@in.ibm.com> (raw)
In-Reply-To: <CAKohpo=k-e1GLiLRNtJ3Xi3+NUWW1+gvtCNr_4Ag60j49dZvdQ@mail.gmail.com>
On Fri, Mar 21, 2014 at 05:15:34PM +0530, Viresh Kumar wrote:
> On 21 March 2014 16:34, Gautham R Shenoy <ego@linux.vnet.ibm.com> wrote:
> > Heh! Well, that wasn't the reason why this was sent out as a separate
> > patch, but never mind. Though I don't understand why it would be
> > difficult to review the patch though.
>
> Because the initial driver wasn't complete earlier. There were 2-3 patches
> after the first one which are changing what the first patch has added.
> Nothing else :)
>
> >> > +static void powernv_read_cpu_freq(void *ret_freq)
> >> > +{
> >> > + unsigned long pmspr_val;
> >> > + s8 local_pstate_id;
> >> > + int *cur_freq, freq, pstate_id;
> >> > +
> >> > + cur_freq = (int *)ret_freq;
> >>
> >> You don't need cur_freq variable at all..
> >
> > I don't like it either. But the compiler complains without this hack
> > :-(
>
> Why would the compiler warn for doing this?:
>
> *(int *)ret_freq = freq;
The compiler doesn't complain if I do this.
>
> >> > + pmspr_val = get_pmspr(SPRN_PMSR);
> >> > +
> >> > + /* The local pstate id corresponds bits 48..55 in the PMSR.
> >> > + * Note: Watch out for the sign! */
> >> > + local_pstate_id = (pmspr_val >> 48) & 0xFF;
> >> > + pstate_id = local_pstate_id;
> >>
> >> similarly local_pstate_id
> >
> > well, I am interested in the bits 48..55 of pmspr_val. That's the
> > pstate_id which can be negative. So I'll like to keep
> > local_pstate_id.
>
> Can you please explain at bit level how getting the value in a s8
> first and then into a s32 will help you here? Instead of getting it
> directly into s32.
Consider the case when pmspr = 0x00feffffffffffff;
We are interested in extracting the value 'fe'. And ensure that when
we store this value into an int, we get the sign extension right.
So the following doesn't work:
pstate_id = (pmspr_val >> 48) & 0xFFFFFFFF;
Since we get pstate_id = 0x000000fe, which is not the same as
0xfffffffe.
Of course, we could do the following, but I wasn't sure if
two levels of type casting helped on the readability front.
pstate_id = (int) ((s8)((pmspr_val >> 48) & 0xFF));
--
Thanks and Regards
gautham.
>
next prev parent reply other threads:[~2014-03-21 13:05 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-20 12:10 [PATCH v3 0/5] powernv: Enable Dynamic Frequency Gautham R. Shenoy
2014-03-20 12:10 ` [PATCH v3 1/5] powernv: cpufreq driver for powernv platform Gautham R. Shenoy
2014-03-21 8:41 ` Viresh Kumar
2014-03-21 10:43 ` Gautham R Shenoy
2014-03-21 10:54 ` Viresh Kumar
2014-03-21 11:40 ` Srivatsa S. Bhat
2014-03-21 13:23 ` Gautham R Shenoy
2014-03-21 13:34 ` Viresh Kumar
2014-03-21 14:54 ` Gautham R Shenoy
2014-03-22 3:43 ` Viresh Kumar
2014-03-21 14:48 ` Vaidyanathan Srinivasan
2014-03-22 3:43 ` Viresh Kumar
2014-03-21 11:45 ` Srivatsa S. Bhat
2014-03-21 11:47 ` Viresh Kumar
2014-03-20 12:10 ` [PATCH v3 2/5] powernv, cpufreq:Add per-core locking to serialize frequency transitions Gautham R. Shenoy
2014-03-21 6:24 ` Gautham R Shenoy
2014-03-21 8:42 ` Viresh Kumar
2014-03-21 9:56 ` Srivatsa S. Bhat
2014-03-20 12:10 ` [PATCH v3 3/5] powernv:cpufreq: Create pstate_id_to_freq() helper Gautham R. Shenoy
2014-03-21 6:24 ` Gautham R Shenoy
2014-03-20 12:10 ` [PATCH v3 4/5] powernv:cpufreq: Export nominal frequency via sysfs Gautham R. Shenoy
2014-03-21 8:47 ` Viresh Kumar
2014-03-21 9:55 ` Gautham R Shenoy
2014-03-21 9:57 ` Viresh Kumar
2014-03-20 12:11 ` [PATCH v3 5/5] powernv:cpufreq: Implement the driver->get() method Gautham R. Shenoy
2014-03-21 6:25 ` Gautham R Shenoy
2014-03-21 9:31 ` Viresh Kumar
2014-03-21 11:04 ` Gautham R Shenoy
2014-03-21 11:45 ` Viresh Kumar
2014-03-21 12:01 ` David Laight
2014-03-21 12:31 ` Gautham R Shenoy
2014-03-21 12:34 ` Viresh Kumar
2014-03-21 15:01 ` David Laight
2014-03-21 13:04 ` Gautham R Shenoy [this message]
2014-03-21 13:12 ` Viresh Kumar
2014-03-21 14:25 ` Gautham R Shenoy
2014-03-21 22:56 ` Benjamin Herrenschmidt
2014-03-22 7:53 ` Gautham R Shenoy
2014-03-21 7:46 ` [PATCH v3 0/5] powernv: Enable Dynamic Frequency Viresh Kumar
2014-03-21 8:19 ` Gautham R Shenoy
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