Re: [PATCH v3 47/47] arm_mpam: Quirk CMN-650's CSU NRDY behaviour

[Gavin Shan <gshan@redhat.com>]

On 1/13/26 12:59 AM, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
> 
> 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.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
>   Documentation/arch/arm64/silicon-errata.rst |  3 +++
>   drivers/resctrl/mpam_devices.c              | 12 ++++++++++++
>   drivers/resctrl/mpam_internal.h             |  6 ++++++
>   3 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
> index e810b2a8f40e..3667650036fb 100644
> --- a/Documentation/arch/arm64/silicon-errata.rst
> +++ b/Documentation/arch/arm64/silicon-errata.rst
> @@ -213,6 +213,9 @@ stable kernels.
>   | ARM            | GIC-700         | #2941627        | ARM64_ERRATUM_2941627       |
>   +----------------+-----------------+-----------------+-----------------------------+
>   +----------------+-----------------+-----------------+-----------------------------+
> +| ARM            | CMN-650         | #3642720        | N/A                         |
> ++----------------+-----------------+-----------------+-----------------------------+
> ++----------------+-----------------+-----------------+-----------------------------+
>   | Broadcom       | Brahma-B53      | N/A             | ARM64_ERRATUM_845719        |
>   +----------------+-----------------+-----------------+-----------------------------+
>   | Broadcom       | Brahma-B53      | N/A             | ARM64_ERRATUM_843419        |
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 7409cb7edab4..e6c9ddaa60e2 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -691,6 +691,12 @@ static const struct mpam_quirk mpam_quirks[] = {
>   	.iidr_mask  = MPAM_IIDR_MATCH_ONE,
>   	.workaround = T241_MBW_COUNTER_SCALE_64,
>   	},
> +	{
> +	/* ARM CMN-650 CSU erratum 3642720 */
> +	.iidr       = MPAM_IIDR_ARM_CMN_650,
> +	.iidr_mask  = MPAM_IIDR_MATCH_ONE,
> +	.workaround = IGNORE_CSU_NRDY,
> +	},
>   	{ NULL } /* Sentinel */
>   };
>   
> @@ -1003,6 +1009,7 @@ struct mon_read {
>   	enum mpam_device_features	type;
>   	u64				*val;
>   	int				err;
> +	bool				waited_timeout;
>   };
>   
>   static bool mpam_ris_has_mbwu_long_counter(struct mpam_msc_ris *ris)
> @@ -1249,6 +1256,10 @@ static void __ris_msmon_read(void *arg)
>   		if (mpam_has_feature(mpam_feat_msmon_csu_hw_nrdy, rprops))
>   			nrdy = now & MSMON___NRDY;
>   		now = FIELD_GET(MSMON___VALUE, now);
> +
> +		if (mpam_has_quirk(IGNORE_CSU_NRDY, msc) && m->waited_timeout)
> +			nrdy = false;
> +
>   		break;
>   	case mpam_feat_msmon_mbwu_31counter:
>   	case mpam_feat_msmon_mbwu_44counter:
> @@ -1386,6 +1397,7 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
>   			.ctx = ctx,
>   			.type = type,
>   			.val = val,
> +			.waited_timeout = true,
>   		};
>   		*val = 0;
>   
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 1680d1036472..0bd323728b53 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -226,6 +226,7 @@ enum mpam_device_quirks {
>   	T241_SCRUB_SHADOW_REGS,
>   	T241_FORCE_MBW_MIN_TO_ONE,
>   	T241_MBW_COUNTER_SCALE_64,
> +	IGNORE_CSU_NRDY,
>   	MPAM_QUIRK_LAST
>   };
>   
> @@ -251,6 +252,11 @@ struct mpam_quirk {
>   				FIELD_PREP_CONST(MPAMF_IIDR_REVISION,    0)	| \
>   				FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0x36b)
>   
> +#define MPAM_IIDR_ARM_CMN_650	FIELD_PREP_CONST(MPAMF_IIDR_PRODUCTID,   0)	| \
> +				FIELD_PREP_CONST(MPAMF_IIDR_VARIANT,     0)	| \
> +				FIELD_PREP_CONST(MPAMF_IIDR_REVISION,    0)	| \
> +				FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0x43b)
> +

An error reported by checkpatch.pl as below.

ERROR: Macros with complex values should be enclosed in parentheses
#105: FILE: drivers/resctrl/mpam_internal.h:255:
+#define MPAM_IIDR_ARM_CMN_650	FIELD_PREP_CONST(MPAMF_IIDR_PRODUCTID,   0)	| \
+				FIELD_PREP_CONST(MPAMF_IIDR_VARIANT,     0)	| \
+				FIELD_PREP_CONST(MPAMF_IIDR_REVISION,    0)	| \
+				FIELD_PREP_CONST(MPAMF_IIDR_IMPLEMENTER, 0x43b)


>   /* The values for MSMON_CFG_MBWU_FLT.RWBW */
>   enum mon_filter_options {
>   	COUNT_BOTH	= 0,

Thanks,
Gavin