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    SubjectRe: [PATCH] cpufreq: set value of CPUFREQ_BOOST_FREQ to 0xABABABAB
    On Mon, Mar 24, 2014 at 12:18:14PM +0530, Viresh Kumar wrote:
    > Ideally, .driver_data field of struct cpufreq_frequency_table must not be used
    > by core at all. But during a recent change if its value is same as
    > CPUFREQ_BOOST_FREQ macro, then it is treated specially by core.
    >
    > The value of this macro was set to ~2 earlier, i.e. 0xFFFFFFFD. In case some
    > driver is using this field for its own data and sets this field to -3, then with
    > two's complement that value will also become 0xFFFFFFFD.
    >
    > To fix this issue, lets change value of this flag to a very uncommon value which
    > shouldn't be used by any driver unless they want to use BOOST
    > feature
    >
    > Along with this update comments to make this more clear.
    >
    > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
    > ---
    >
    > Gautham/Vaidy: I hope this fixes the problem we discussed for your
    > patchset.

    Since the type of .driver_data is "unsigned int", the cpufreq core
    seems to be assuming that the value cannot be -ve. So, drivers should
    be storing -ve values in these fields at their own risk. Because apart
    from determining whether the corresponding frequency is a boost
    frequency or not, the cpufreq core seems to be using the .driver_data
    field in pr_debugs(). The value of .driver_data formatted as "%u" is
    not useful in these pr_debugs, if the driver stores -ve value in this
    field.

    On the other hand, if we change the type of .driver_data to "int" then
    restricting the driver to not use specific values is unreasonable
    since .driver_data field is supposed to be private to the driver and
    the core is not supposed to intepret it. In which case we should
    be having a separate field for determining if the frequency is a BOOST
    frequency or not.

    So while it fixes the problem for us, I don't think this patch fixes
    the problem in general for the reasons mentioned above.

    --
    Thanks and Regards
    gautham.

    >
    > include/linux/cpufreq.h | 10 ++++++++--
    > 1 file changed, 8 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
    > index c48e595..9f25d9d 100644
    > --- a/include/linux/cpufreq.h
    > +++ b/include/linux/cpufreq.h
    > @@ -455,12 +455,18 @@ extern struct cpufreq_governor cpufreq_gov_conservative;
    > * FREQUENCY TABLE HELPERS *
    > *********************************************************************/
    >
    > +/* Special Values of .frequency field */
    > #define CPUFREQ_ENTRY_INVALID ~0
    > #define CPUFREQ_TABLE_END ~1
    > -#define CPUFREQ_BOOST_FREQ ~2
    > +/* Special Values of .driver_data field */
    > +#define CPUFREQ_BOOST_FREQ 0xABABABAB
    >
    > struct cpufreq_frequency_table {
    > - unsigned int driver_data; /* driver specific data, not used by core */
    > + /*
    > + * driver specific data, not used by core unless it is set to
    > + * CPUFREQ_BOOST_FREQ.
    > + */
    > + unsigned int driver_data;
    > unsigned int frequency; /* kHz - doesn't need to be in ascending
    > * order */
    > };
    > --
    > 1.7.12.rc2.18.g61b472e
    >



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