[PATCH v4 2/2] perf/arm-cmn: Add workarounds for CMN-S3 on Graviton5

[Robin Murphy]

On 2026-05-31 12:04 pm, Aviv Bakal wrote:
> Graviton5 uses a customised CMN-S3 implementation where certain
> discovery registers report zeroed fields. Add the following workarounds:
> 
>   - Introduce a dedicated ACPI HID to identify the Graviton5 CMN variant.
>   - Derive the DTC domain from the XP node ID, since the unit info
>     register reports it as zero.
>   - Set the DTC logical ID from the XP's logical ID, since the node info
>     register's logical ID field is also zeroed.

Reviewed-by: Robin Murphy <robin.murphy at arm.com>

> Signed-off-by: Aviv Bakal <avivb at amazon.com>
> ---
>   drivers/perf/arm-cmn.c | 32 +++++++++++++++++++++++++++++++-
>   1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index f1978a53d1c1..3fb71d9a57eb 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -31,7 +31,8 @@
>   #define CMN_CHILD_NODE_ADDR		GENMASK(29, 0)
>   #define CMN_CHILD_NODE_EXTERNAL		BIT(31)
>   
> -#define CMN_MAX_DIMENSION		12
> +/* Some implementations use a mesh larger than the architectural max of 12 */
> +#define CMN_MAX_DIMENSION		14
>   #define CMN_MAX_XPS			(CMN_MAX_DIMENSION * CMN_MAX_DIMENSION)
>   #define CMN_MAX_DTMS			(CMN_MAX_XPS + (CMN_MAX_DIMENSION - 1) * 4)
>   
> @@ -214,6 +215,8 @@ enum cmn_part {
>   	PART_CMN700 = 0x43c,
>   	PART_CI700 = 0x43a,
>   	PART_CMN_S3 = 0x43e,
> +	/* Synthetic part number, overridden to PART_CMN_S3 during discovery */
> +	PART_GRAVITON5 = 0xa5,
>   };
>   
>   /* CMN-600 r0px shouldn't exist in silicon, thankfully */
> @@ -2250,6 +2253,18 @@ static unsigned int arm_cmn_dtc_domain(struct arm_cmn *cmn, void __iomem *xp_reg
>   	return FIELD_GET(CMN_DTM_UNIT_INFO_DTC_DOMAIN, readl_relaxed(xp_region + offset));
>   }
>   
> +static unsigned int arm_cmn_graviton5_dtc_domain(u16 xp_id)
> +{
> +	unsigned int x = (xp_id >> 7) & 0xf;
> +	unsigned int y = (xp_id >> 3) & 0xf;
> +
> +	/*
> +	 * The unit info register reads as zero; derive the DTC domain from
> +	 * the XP's mesh coordinates over the 10x14 mesh.
> +	 */
> +	return (x / 5) + (y / 7) * 2;
> +}
> +
>   static void arm_cmn_init_node_info(struct arm_cmn *cmn, u32 offset, struct arm_cmn_node *node)
>   {
>   	int level;
> @@ -2295,6 +2310,7 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
>   	u64 reg;
>   	int i, j;
>   	size_t sz;
> +	bool graviton5_workaround = false;
>   
>   	arm_cmn_init_node_info(cmn, rgn_offset, &cfg);
>   	if (cfg.type != CMN_TYPE_CFG)
> @@ -2305,6 +2321,13 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
>   	reg = readq_relaxed(cfg_region + CMN_CFGM_PERIPH_ID_01);
>   	part = FIELD_GET(CMN_CFGM_PID0_PART_0, reg);
>   	part |= FIELD_GET(CMN_CFGM_PID1_PART_1, reg) << 8;
> +
> +	/* Graviton5 has a customised CMN-S3 which needs some fixups */
> +	if (cmn->part == PART_GRAVITON5) {
> +		cmn->part = PART_CMN_S3;
> +		graviton5_workaround = true;
> +	}
> +
>   	/* 600AE is close enough that it's not really worth more complexity */
>   	if (part == PART_CMN600AE)
>   		part = PART_CMN600;
> @@ -2394,6 +2417,8 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
>   
>   		if (cmn->part == PART_CMN600)
>   			xp->dtc = -1;
> +		else if (graviton5_workaround)
> +			xp->dtc = arm_cmn_graviton5_dtc_domain(xp->id);
>   		else
>   			xp->dtc = arm_cmn_dtc_domain(cmn, xp_region);
>   
> @@ -2472,6 +2497,10 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
>   
>   			switch (dn->type) {
>   			case CMN_TYPE_DTC:
> +				if (graviton5_workaround) {
> +					/* Node info logical ID is zeroed; use the XP's */
> +					dn->logid = xp->logid;
> +				}
>   				cmn->num_dtcs++;
>   				dn++;
>   				break;
> @@ -2687,6 +2716,7 @@ static const struct acpi_device_id arm_cmn_acpi_match[] = {
>   	{ "ARMHC650" },
>   	{ "ARMHC700" },
>   	{ "ARMHC003" },
> +	{ "AMZN0070", PART_GRAVITON5 },
>   	{}
>   };
>   MODULE_DEVICE_TABLE(acpi, arm_cmn_acpi_match);