On Mon, Apr 01, 2019 at 11:05:04AM -0700, Evan Green wrote: > The PMC driver performs a 32-bit read on the sleep s0 residency counter, > followed by a hard-coded multiplication to convert into microseconds. > The maximum value this counter could have would be 0xffffffff*0x64 > microseconds, which by my calculations is about 4.9 days. This is well > within a reasonable time period to observe an overflow. > > Usermode consumers watching slp_s0_residency_usec need to be aware of > overflows, but have no idea what the maximum value of this counter is, > given the hardcoded multiply of a 32-bit value by > SPT_PMC_SLP_S0_RES_COUNTER_STEP. This register is a 32 bit register untill ICL generation and a recent patch from Rajat fixed the overflow https://patchwork.kernel.org/patch/10816103/ already so i am not sure how this will help userspace. I think the userspace can still take care of any overflow concerns based on the information available about this register in EDS so i feel exposing a new debugfs entry just for the sake of knowing range is probably not needed. > > Expose a slp_s0_residency_usec_range to usermode as well, which returns > the maximum value this counter could have. Consumers can use this to > manage rollovers. > > Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx> > > --- > > Note: I also looked at a similar bit of functionality in > intel_pmc_s0ix_counter_read(), but noticed it's doing a 64-bit register > access. Is the counter being read here in pmc_core_dev_state_get() > (weird name btw) actually 64-bits long? If so, we can abandon this change > and just create a fix to return the full extended value. > > --- > drivers/platform/x86/intel_pmc_core.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c > index f2c621b55f49..bec54be9be93 100644 > --- a/drivers/platform/x86/intel_pmc_core.c > +++ b/drivers/platform/x86/intel_pmc_core.c > @@ -396,6 +396,14 @@ static int pmc_core_dev_state_get(void *data, u64 *val) > > DEFINE_DEBUGFS_ATTRIBUTE(pmc_core_dev_state, pmc_core_dev_state_get, NULL, "%llu\n"); > > +static int pmc_core_slp_s0_range_get(void *data, u64 *val) > +{ > + *val = pmc_core_adjust_slp_s0_step(0xffffffff); > + return 0; > +} > + > +DEFINE_DEBUGFS_ATTRIBUTE(pmc_core_slp_s0_range, pmc_core_slp_s0_range_get, NULL, "%llu\n"); > + > static int pmc_core_check_read_lock_bit(void) > { > struct pmc_dev *pmcdev = &pmc; > @@ -764,6 +772,9 @@ static int pmc_core_dbgfs_register(struct pmc_dev *pmcdev) > debugfs_create_file("slp_s0_residency_usec", 0444, dir, pmcdev, > &pmc_core_dev_state); > > + debugfs_create_file("slp_s0_residency_usec_range", 0444, dir, pmcdev, > + &pmc_core_slp_s0_range); > + > debugfs_create_file("pch_ip_power_gating_status", 0444, dir, pmcdev, > &pmc_core_ppfear_fops); > > -- > 2.20.1 > -- Best Regards, Rajneesh
