[PATCH] arm_mpam: Warn when firmware leaves PARTIDs disabled

[Ben Horgan]

Hi Ping,

On 27/10/2026 08:35, Ping Li wrote:
> MPAMF_IDR.HAS_ENDIS indicates the MSC supports the MPAMCFG_EN_FLAGS
> PARTID enable/disable feature. Firmware is required to enable all
> PARTIDs at boot before handing over to software that is unaware of
> these registers. A PARTID left disabled silently ignores all resctrl
> schemata changes, as its traffic is treated as having no resources.
> 
> Debugging an IP that implements HAS_ENDIS but had no visible effect
> from resctrl took a while to root cause. The fix belongs in firmware,

I can see how this would be frustrating. In general, we can't rely on firmware to do the reset
correctly e.g. after a kexec. Hence, I'd rather enable all the PARTID as part of the mpam driver
initialization in the same way that we set all the controls to be non-throttling.

I do have a preliminary patch but there seems to be some contradictions in the specification so I
haven't posted it yet.

There are three points of confusion I'm aware of. Firstly, R-CSLHH says the enabled status is not
affected by narrowing and so just applies to the reqPARTID but the descriptions of MPAMCFG_EN and
MPAMCFG_EN_FLAGS indicate that it effects the intPARTID. Secondly, what happens if MPAMCFG_EN.PARTID
and PARTID_SEL are different? Thirdly, is ENDIS RIS-sensitive or a global setting for the MSC.

For the last one, the conclusion seems to be that it is a global insensitive setting but this is
still not fully reflected in the specification.

I'm not aware of how other ENDIS implementations behave. I have asked for internal clarification on
the points above but perhaps you could raise it with support at arm.com so that the architects are
aware this affects your design.

Thanks,

Ben

> but warn during probe so this misconfiguration is reported loudly
> instead of silently.
> 
> Signed-off-by: Ping Li <leeonion.muyu at gmail.com>
> ---
>  drivers/resctrl/mpam_devices.c  | 16 ++++++++++++++++
>  drivers/resctrl/mpam_internal.h |  2 ++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 48adc49b833c..f03aa40faa0a 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1159,6 +1159,7 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>  {
>  	int ret;
>  	u64 idr;
> +	u32 en_flags;
>  	u16 partid_max;
>  	u8 ris_idx, pmg_max;
>  	struct mpam_msc_ris *ris;
> @@ -1199,6 +1200,21 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>  			ret = mpam_msc_read_idr(msc, &idr);
>  			if (ret)
>  				return ret;
> +
> +			/*
> +			 * Firmware must enable all PARTIDs before handing the
> +			 * system to software that is unaware of EN_FLAGS, so
> +			 * a disabled PARTID here means resctrl schemata
> +			 * changes silently have no effect.
> +			 */
> +			if (FIELD_GET(MPAMF_IDR_HAS_ENDIS, idr)) {
> +				u32 en_mask = GENMASK(FIELD_GET(MPAMF_IDR_PARTID_MAX, idr) % 32, 0);
> +
> +				ret = __mpam_read_reg(msc, MPAMCFG_EN_FLAGS, &en_flags);
> +				if (!ret && (en_flags & en_mask) != en_mask)
> +					dev_err_once(dev,
> +						     "firmware left PARTIDs disabled, schemata changes will not take effect\n");
> +			}
>  		}
>  
>  		partid_max = FIELD_GET(MPAMF_IDR_PARTID_MAX, idr);
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 1f86cc158100..008dc4e10f38 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -574,6 +574,7 @@ int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
>  #define MPAMCFG_MBW_MIN		0x0200  /* min mem-bw config */
>  #define MPAMCFG_MBW_MAX		0x0208  /* max mem-bw config */
>  #define MPAMCFG_MBW_WINWD	0x0220  /* mem-bw accounting window config */
> +#define MPAMCFG_EN_FLAGS	0x0320  /* partid enable flags config */
>  #define MPAMCFG_MBW_PBM		0x2000  /* mem-bw portion bitmap config */
>  #define MPAMCFG_PRI		0x0400  /* priority partitioning config */
>  #define MPAMCFG_MBW_PROP	0x0500  /* mem-bw stride config */
> @@ -608,6 +609,7 @@ int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
>  #define MPAMF_IDR_HAS_RIS		BIT(32)
>  #define MPAMF_IDR_HAS_EXTD_ESR		BIT(38)
>  #define MPAMF_IDR_HAS_ESR		BIT(39)
> +#define MPAMF_IDR_HAS_ENDIS		BIT(42)
>  #define MPAMF_IDR_RIS_MAX		GENMASK(59, 56)
>  
>  /* MPAMF_MSMON_IDR - MPAM performance monitoring ID register */