linux-kernel - Re: [PATCH 1/8] perf/arm-cmn: Refactor node ID handling. Again.

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Message-ID: <ab1b89c7-7bf-78d2-50ca-3411e511ec33@os.amperecomputing.com>
Date: Fri, 23 Aug 2024 18:00:33 -0700 (PDT)
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Robin Murphy <robin.murphy@....com>
cc: will@...nel.org, mark.rutland@....com, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
    ilkka@...amperecomputing.com
Subject: Re: [PATCH 1/8] perf/arm-cmn: Refactor node ID handling. Again.



On Fri, 9 Aug 2024, Robin Murphy wrote:
> It transpires that despite the explicit example to the contrary in the
> CMN-700 TRM, the "extra device ports" config is in fact a per-XP thing
> rather than a global one. To that end, rework node IDs yet again to
> carry around the additional data necessary to decode them properly. At
> this point the notion of fully decomposing an ID becomes more
> impractical than it's worth, so unabstracting the XY mesh coordinates
> (where 2/3 users were just debug anyway) ends up leaving things a bit
> simpler overall.
>
> Fixes: 60d1504070c2 ("perf/arm-cmn: Support new IP features")
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> drivers/perf/arm-cmn.c | 94 ++++++++++++++++++------------------------
> 1 file changed, 40 insertions(+), 54 deletions(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index c932d9d355cf..fd2122a37f22 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c

> @@ -357,49 +352,33 @@ struct arm_cmn {
> static int arm_cmn_hp_state;
>
> struct arm_cmn_nodeid {
> -	u8 x;
> -	u8 y;
> 	u8 port;
> 	u8 dev;
> };
>
> static int arm_cmn_xyidbits(const struct arm_cmn *cmn)
> {
> -	return fls((cmn->mesh_x - 1) | (cmn->mesh_y - 1) | 2);
> +	return fls((cmn->mesh_x - 1) | (cmn->mesh_y - 1));
> }
>
> -static struct arm_cmn_nodeid arm_cmn_nid(const struct arm_cmn *cmn, u16 id)
> +static struct arm_cmn_nodeid arm_cmn_nid(const struct arm_cmn_node *dn)
> {
> 	struct arm_cmn_nodeid nid;
>
> -	if (cmn->num_xps == 1) {
> -		nid.x = 0;
> -		nid.y = 0;
> -		nid.port = CMN_NODEID_1x1_PID(id);
> -		nid.dev = CMN_NODEID_DEVID(id);
> -	} else {
> -		int bits = arm_cmn_xyidbits(cmn);
> -
> -		nid.x = CMN_NODEID_X(id, bits);
> -		nid.y = CMN_NODEID_Y(id, bits);
> -		if (cmn->ports_used & 0xc) {
> -			nid.port = CMN_NODEID_EXT_PID(id);
> -			nid.dev = CMN_NODEID_EXT_DEVID(id);
> -		} else {
> -			nid.port = CMN_NODEID_PID(id);
> -			nid.dev = CMN_NODEID_DEVID(id);
> -		}
> -	}
> +	nid.dev = dn->id & ((1U << dn->deviceid_bits) - 1);
> +	nid.port = (dn->id >> dn->deviceid_bits) & ((1U << dn->portid_bits) - 1);
> 	return nid;
> }
>
> static struct arm_cmn_node *arm_cmn_node_to_xp(const struct arm_cmn *cmn,
> 					       const struct arm_cmn_node *dn)
> {
> -	struct arm_cmn_nodeid nid = arm_cmn_nid(cmn, dn->id);
> -	int xp_idx = cmn->mesh_x * nid.y + nid.x;
> +	int id = dn->id >> (dn->portid_bits + dn->deviceid_bits);
> +	int bits = arm_cmn_xyidbits(cmn);
> +	int x = id > bits;
                   ^^^

Instead of comparison, shouldn't that be bit shift?

Cheers, Ilkka

> +	int y = id & ((1U << bits) - 1);
>
> -	return cmn->xps + xp_idx;
> +	return cmn->xps + cmn->mesh_x * y + x;
> }
> static struct arm_cmn_node *arm_cmn_node(const struct arm_cmn *cmn,
> 					 enum cmn_node_type type)
>