linux-kernel - Re: [PATCH] cpufreq: don't print value of .driver

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Date:	Thu, 27 Mar 2014 16:56:03 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"ego@...ux.vnet.ibm.com" <ego@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH] cpufreq: don't print value of .driver_data from core

On Thu, Mar 27, 2014 at 04:29:37PM +0530, Viresh Kumar wrote:
> On 27 March 2014 16:18, Gautham R Shenoy <ego@...ux.vnet.ibm.com> wrote:
> > So after this patch, driver_data is only going to be used by drivers
> > which want an "unsigned int" value to be saved along with the
> > frequency in the frequency_table and for those who want to overload
> > its interpretation to indicate BOOST.
> >
> > From the core's stand point, it is useful only for determining whether
> > a frequency is BOOST frequency or not.
> 
> Yes.
> 
> > So, wouldn't it be logical to allow drivers maintain their own driver
> > data since the core is anyway not interested in it, and change this
> > .driver_data to "flags" or some such which can indicate boost ?
> 
> We can add another field .flags in case Rafael doesn't accept the
> other proposal I sent for fixing BOOST issue.

Even with that patch, the .driver_data won't be opaque. And that's not
good. Because, while some driver might not be explicitly setting the
value of .driver_data to 0xABABABAB, it might want to store the value
obtained at runtime into this field. And it could so happen
that at runtime this value is 0xABABABAB.

> 
> But the point behind keeping .driver_data field here was: many drivers
> have some information attached to each frequency and they are closely
> bound to each other. And so it made more sense to keep them together.
> This is still used by many drivers and I wouldn't like them to maintain
> separate arrays for keeping this information. They are so much bound
> to the frequencies at the same index, that keeping them separately
> wouldn't be a good idea.

I understand this part. However there might be more data than an
"unsigned int" that the drivers would like to be bound at the same
index. Voltage information, for instance.

> 
--
Thanks and Regards
gautham.

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