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