Hi Gavin,
On 1/19/26 06:50, Gavin Shan wrote:
> Hi Ben,
>
> On 1/13/26 12:58 AM, Ben Horgan wrote:
>> From: James Morse <james.morse@arm.com>
>>
>> The MPAM system registers will be lost if the CPU is reset during PSCI's
>> CPU_SUSPEND.
>>
>> Add a PM notifier to restore them.
>>
>> mpam_thread_switch(current) can't be used as this won't make any
>> changes if
>> the in-memory copy says the register already has the correct value. In
>> reality the system register is UNKNOWN out of reset.
>>
>> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
>> ---
>> arch/arm64/kernel/mpam.c | 30 ++++++++++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>>
>
> One question below...
>
>> diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
>> index e6feff2324ac..dbe0a2d05abb 100644
>> --- a/arch/arm64/kernel/mpam.c
>> +++ b/arch/arm64/kernel/mpam.c
>> @@ -4,6 +4,7 @@
>> #include <asm/mpam.h>
>> #include <linux/arm_mpam.h>
>> +#include <linux/cpu_pm.h>
>> #include <linux/jump_label.h>
>> #include <linux/percpu.h>
>> @@ -13,12 +14,41 @@ DEFINE_PER_CPU(u64, arm64_mpam_current);
>> u64 arm64_mpam_global_default;
>> +static int mpam_pm_notifier(struct notifier_block *self,
>> + unsigned long cmd, void *v)
>> +{
>> + u64 regval;
>> + int cpu = smp_processor_id();
>> +
>> + switch (cmd) {
>> + case CPU_PM_EXIT:
>> + /*
>> + * Don't use mpam_thread_switch() as the system register
>> + * value has changed under our feet.
>> + */
>> + regval = READ_ONCE(per_cpu(arm64_mpam_current, cpu));
>> + write_sysreg_s(regval, SYS_MPAM1_EL1);
>> + isb();
>> +
>> + write_sysreg_s(regval, SYS_MPAM0_EL1);
>> +
>> + return NOTIFY_OK;
>> + default:
>> + return NOTIFY_DONE;
>> + }
>> +}
>> +
>> +static struct notifier_block mpam_pm_nb = {
>> + .notifier_call = mpam_pm_notifier,
>> +};
>> +
>> static int __init arm64_mpam_register_cpus(void)
>> {
>> u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
>> u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
>> u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);
>> + cpu_pm_register_notifier(&mpam_pm_nb);
>
> Need we ensure MPAM capability exists in the hardware before the
> notifier is registerred?
> Otherwise, mpam_pm_notifier() can accesses SYS_MPAM0_EL1 and
> SYS_MPAM1_EL1 system registers
> which may not supported by the hardware.
Ah yes, I'll add a system_supports_mpam() check here.
>
>> return mpam_register_requestor(partid_max, pmg_max);
>> }
>> /* Must occur before mpam_msc_driver_init() from subsys_initcall() */
>
> Thanks,
> Gavin
>
Thanks,
Ben