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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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