From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: mcx: remove MCX_MAX_QUEUES
To: Jonathan Matthew <jonathan@d14n.org>
Cc: tech@openbsd.org
Date: Tue, 18 Nov 2025 19:52:57 +0100

On Tue, Nov 18, 2025 at 05:02:49PM +1000, Jonathan Matthew wrote:
> Now that we have IF_MAX_VECTORS as a limit on the number of queues an
> interface will set up, MCX_MAX_QUEUES is kind of pointless - the
> relevant limits are the size of the msi-x table and the maximum number of
> event queues the nic will let us create.
> 
> This diff removes MCX_MAX_QUEUES, using IF_MAX_VECTORS instead where
> appropriate, and adds the EQ limit to the calculation.  The EQ limit
> might not ever be the limiting factor as generally the msi-x table is
> smaller, but it's easy to account for it here.
> 
> ok?

OK bluhm@

> Index: if_mcx.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pci/if_mcx.c,v
> diff -u -p -r1.120 if_mcx.c
> --- if_mcx.c	11 Nov 2025 17:43:18 -0000	1.120
> +++ if_mcx.c	18 Nov 2025 06:20:34 -0000
> @@ -90,8 +90,6 @@ enum mcx_cmdq_slot {
>  #define MCX_LOG_RQ_SIZE			10
>  #define MCX_LOG_SQ_SIZE			11
>  
> -#define MCX_MAX_QUEUES			16
> -
>  /* completion event moderation - about 10khz, or 90% of the cq */
>  #define MCX_CQ_MOD_PERIOD		50
>  #define MCX_CQ_MOD_COUNTER		\
> @@ -121,8 +119,8 @@ CTASSERT(ETHER_HDR_LEN + ETHER_VLAN_ENCA
>  #define MCX_WQ_DOORBELL_BASE		MCX_PAGE_SIZE/2
>  #define MCX_WQ_DOORBELL_STRIDE		64
>  /* make sure the doorbells fit */
> -CTASSERT(MCX_MAX_QUEUES * MCX_CQ_DOORBELL_STRIDE < MCX_WQ_DOORBELL_BASE);
> -CTASSERT(MCX_MAX_QUEUES * MCX_WQ_DOORBELL_STRIDE <
> +CTASSERT(IF_MAX_VECTORS * MCX_CQ_DOORBELL_STRIDE < MCX_WQ_DOORBELL_BASE);
> +CTASSERT(IF_MAX_VECTORS * MCX_WQ_DOORBELL_STRIDE <
>      MCX_DOORBELL_AREA_SIZE - MCX_WQ_DOORBELL_BASE);
>  
>  #define MCX_WQ_DOORBELL_MASK		0xffff
> @@ -2482,6 +2480,7 @@ struct mcx_softc {
>  
>  	struct mcx_dmamem	 sc_doorbell_mem;
>  
> +	int			 sc_max_eqs;
>  	struct mcx_eq		 sc_admin_eq;
>  	struct mcx_eq		 sc_queue_eq;
>  
> @@ -2934,7 +2933,7 @@ mcx_attach(struct device *parent, struct
>  
>  	msix--; /* admin ops took one */
>  	sc->sc_intrmap = intrmap_create(&sc->sc_dev, msix,
> -	    MIN(MCX_MAX_QUEUES, IF_MAX_VECTORS), INTRMAP_POWEROF2);
> +	    MIN(sc->sc_max_eqs, IF_MAX_VECTORS), INTRMAP_POWEROF2);
>  	if (sc->sc_intrmap == NULL) {
>  		printf(": unable to create interrupt map\n");
>  		goto teardown;
> @@ -4046,6 +4045,8 @@ mcx_hca_max_caps(struct mcx_softc *sc)
>  	sc->sc_mhz = bemtoh32(&hca->device_frequency_mhz);
>  	sc->sc_khz = bemtoh32(&hca->device_frequency_khz);
>  
> +	sc->sc_max_eqs = 1 << (hca->log_max_eq & MCX_CAP_DEVICE_LOG_MAX_EQ);
> +
>  free:
>  	mcx_dmamem_free(sc, &mxm);
>  
> @@ -7303,7 +7304,7 @@ mcx_up(struct mcx_softc *sc)
>  	struct mcx_flow_match match_crit;
>  	struct mcx_rss_rule *rss;
>  	uint32_t dest;
> -	int rqns[MCX_MAX_QUEUES];
> +	int rqns[IF_MAX_VECTORS];
>  
>  	if (mcx_create_tis(sc, &sc->sc_tis) != 0)
>  		goto down;