Re: [PATCH 15/33] arm_mpam: Add helpers for managing the locking around the mon_sel registers

[Gavin Shan]

On 11/7/25 10:34 PM, Ben Horgan wrote:
> From: James Morse <james.morse@xxxxxxx>
>
> The MSC MON_SEL register needs to be accessed from hardirq for the overflow
> interrupt, and when taking an IPI to access these registers on platforms
> where MSC are not accessible from every CPU. This makes an irqsave
> spinlock the obvious lock to protect these registers. On systems with SCMI
> or PCC mailboxes it must be able to sleep, meaning a mutex must be used.
> The SCMI or PCC platforms can't support an overflow interrupt, and
> can't access the registers from hardirq context.
>
> Clearly these two can't exist for one MSC at the same time.
>
> Add helpers for the MON_SEL locking. For now, use a irqsave spinlock and
> only support 'real' MMIO platforms.
>
> In the future this lock will be split in two allowing SCMI/PCC platforms
> to take a mutex. Because there are contexts where the SCMI/PCC platforms
> can't make an access, mpam_mon_sel_lock() needs to be able to fail. Do
> this now, so that all the error handling on these paths is present. This
> allows the relevant paths to fail if they are needed on a platform where
> this isn't possible, instead of having to make explicit checks of the
> interface type.
>
> Tested-by: Fenghua Yu <fenghuay@xxxxxxxxxx>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> Tested-by: Peter Newman <peternewman@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
> ---
> Changes since v3:
> use devm_mutex_init()
> include tiying
> stray comma (Jonathan)
> ---
>   drivers/resctrl/mpam_devices.c  |  2 ++
>   drivers/resctrl/mpam_internal.h | 39 +++++++++++++++++++++++++++++++++
>   2 files changed, 41 insertions(+)

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>