Re: [PATCH v6 39/40] arm_mpam: Quirk CMN-650's CSU NRDY behaviour

[Gavin Shan]

On 3/14/26 12:46 AM, Ben Horgan wrote:
> From: James Morse <james.morse@xxxxxxx>
>
> CMN-650 is afflicted with an erratum where the CSU NRDY bit never clears.
> This tells us the monitor never finishes scanning the cache. The erratum
> document says to wait the maximum time, then ignore the field.
>
> Add a flag to indicate whether this is the final attempt to read the
> counter, and when this quirk is applied, ignore the NRDY field.
>
> This means accesses to this counter will always retry, even if the counter
> was previously programmed to the same values.
>
> The counter value is not expected to be stable, it drifts up and down with
> each allocation and eviction. The CSU register provides the value for a
> point in time.
>
> Reviewed-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
> ---
> Changes since v3:
> parentheses in macro
> ---
>   Documentation/arch/arm64/silicon-errata.rst |  3 +++
>   drivers/resctrl/mpam_devices.c              | 12 ++++++++++++
>   drivers/resctrl/mpam_internal.h             |  6 ++++++
>   3 files changed, 21 insertions(+)

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>