Messages in this thread | | | Date | Tue, 24 Oct 2023 09:14:17 +0100 | Subject | Re: [PATCH v4 06/18] PM: EM: Check if the get_cost() callback is present in em_compute_costs() | From | Lukasz Luba <> |
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On 10/23/23 19:23, Daniel Lezcano wrote: > On 25/09/2023 10:11, Lukasz Luba wrote: >> The em_compute_cost() is going to be re-used in runtime modified EM >> code path. Thus, make sure that this common code is safe and won't >> try to use the NULL pointer. The former em_compute_cost() didn't have to >> care about runtime modification code path. The upcoming changes introduce >> such option, but with different callback. Those two paths which use >> get_cost() (during first EM registration) or update_power() (during >> runtime modification) need to be safely handled in em_compute_costs(). >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> kernel/power/energy_model.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c >> index 7ea882401833..35e07933b34a 100644 >> --- a/kernel/power/energy_model.c >> +++ b/kernel/power/energy_model.c >> @@ -116,7 +116,7 @@ static int em_compute_costs(struct device *dev, >> struct em_perf_state *table, >> for (i = nr_states - 1; i >= 0; i--) { >> unsigned long power_res, cost; >> - if (flags & EM_PERF_DOMAIN_ARTIFICIAL) { >> + if (flags & EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost) { >> ret = cb->get_cost(dev, table[i].frequency, &cost); >> if (ret || !cost || cost > EM_MAX_POWER) { >> dev_err(dev, "EM: invalid cost %lu %d\n", > > I do believe & operator has lower precedence than && operator, thus the > test is actually: > > (flags & (EM_PERF_DOMAIN_ARTIFICIAL && cb->get_cost)) > > but it should be > > ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) > > Right ? >
The bitwise '&' is stronger than logical '&&', so the code will work as in your 2nd example. Although, I will change it and add parentheses for better reading.
Thanks!
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