From: Claudio Jeker <cjeker@diehard.n-r-g.com>
Subject: Re: mwx: implement RSSI
To: Benjamin Lee McQueen <mcq@disroot.org>
Cc: Tech <tech@openbsd.org>
Date: Sat, 2 May 2026 13:31:47 +0200

On Fri, May 01, 2026 at 05:00:48PM -0500, Benjamin Lee McQueen wrote:
> hi tech@,
> 
> attached is a diff that implements RSSI for the MediaTek MT7921 network
> card.
> 
> tested on a MT7921.
> 
> -ben

> --- sys/dev/pci/if_mwx.c	Fri Aug  1 08:37:06 2025
> +++ /usr/src/sys/dev/pci/if_mwx.c	Mon Mar  9 18:45:35 2026
> @@ -1019,7 +1019,7 @@
>  		    htole16(ic->ic_channels[rxi.rxi_chan].ic_freq);
>  		tap->wr_chan_flags =
>  		    ic->ic_channels[rxi.rxi_chan].ic_flags;
> -		tap->wr_dbm_antsignal = 0;
> +		tap->wr_dbm_antsignal = rxi.rxi_rssi;
>  		bpf_mtap_hdr(sc->sc_drvbpf, tap, sc->sc_rxtap_len, m,
>  		    BPF_DIRECTION_IN);
>  	}
> @@ -1029,7 +1029,6 @@
>  	ni = ieee80211_find_rxnode(ic, wh);
>  
>  	/* send the frame to the 802.11 layer */
> -	/* TODO MAYBE rxi.rxi_rssi = rssi; */
>  	ieee80211_inputm(ifp, m, ni, &rxi, ml);
>  
>  	/* node is no longer needed */
> @@ -4225,11 +4224,13 @@
>      struct ieee80211_rxinfo *rxi)
>  {
>  	struct ieee80211com *ic = &sc->sc_ic;
> -	uint32_t *rxd, rxd0, rxd1, rxd2, rxd3, rxd4;
> +	uint32_t *rxd, *rxv = NULL;
> +	uint32_t rxd0, rxd1, rxd2, rxd3, rxd4;
>  //	uint32_t mode = 0;
>  	uint16_t hdr_gap /*, seq_ctrl = 0, fc = 0 */;
>  	uint8_t chfnum, remove_pad /*, qos_ctl = 0, amsdu_info */;
>  	int idx, unicast, num_rxd = 6;
> +	int i;
>  //	bool insert_ccmp_hdr = false;
>  
>  	if (m->m_len < num_rxd * sizeof(uint32_t))
> @@ -4308,16 +4309,53 @@
>  
>  	rxd += 6;
>  
> -	if (rxd1 & MT_RXD1_NORMAL_GROUP_4)
> +	if (rxd1 & MT_RXD1_NORMAL_GROUP_4) {
>  		num_rxd += 4;
> -	if (rxd1 & MT_RXD1_NORMAL_GROUP_1)
> +		rxd += 4;
> +	}
> +	if (rxd1 & MT_RXD1_NORMAL_GROUP_1) {
>  		num_rxd += 4;
> -	if (rxd1 & MT_RXD1_NORMAL_GROUP_2)
> +		rxd += 4;
> +	}
> +	if (rxd1 & MT_RXD1_NORMAL_GROUP_2) {
>  		num_rxd += 2;
> -	if (rxd1 & MT_RXD1_NORMAL_GROUP_3)
> +		rxd += 2;
> +	}
> +	if (rxd1 & MT_RXD1_NORMAL_GROUP_3) {	
> +		uint32_t v0, v1;
> +		int8_t chain[4], signal;
> +
> +		rxv = rxd;
>  		num_rxd += 2;
> -	if (rxd1 & MT_RXD1_NORMAL_GROUP_5)
> -		num_rxd += 18;
> +		rxd += 2;
> +
> +		v0 = le32toh(rxv[0]); /* XXX not implemented yet */ 
> +		v1 = le32toh(rxv[1]);
> +
> +		if (rxd1 & MT_RXD1_NORMAL_GROUP_5) {
> +			num_rxd += 18;
> +			rxd += 6;
> +			rxv = rxd;
> +			v1 = le32toh(rxv[0]); 
> +			rxd += 12;
> +		}
> +	
> +
> +		chain[0] = rcpi_to_rssi(MT_PRXV_RCPI0, v1);
> +		chain[1] = rcpi_to_rssi(MT_PRXV_RCPI1, v1);
> +		chain[2] = rcpi_to_rssi(MT_PRXV_RCPI2, v1);
> +		chain[3] = rcpi_to_rssi(MT_PRXV_RCPI3, v1);
> +
> +		signal = -128;
> +		for (i = 0; i < sc->sc_capa.num_streams; i++) {
> +			if (!(sc->sc_capa.antenna_mask & BIT(i)))
> +				continue;	
> +			if (chain[i] >= 0)
> +				continue;
> +			signal = MAX(signal, chain[i]);
> +		}
> +		rxi->rxi_rssi = signal;
> +	}
>  
>  	if (m->m_len < num_rxd * sizeof(uint32_t))
>  		return -1;
> --- sys/dev/pci/if_mwxreg.h	Wed May 22 02:38:57 2024
> +++ /usr/src/sys/dev/pci/if_mwxreg.h	Mon Mar  9 18:40:42 2026
> @@ -16,6 +16,11 @@
>   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
>   */
>  
> +/* FROM LINUX */
> +#define BIT(x)				(1 << (x))
> +#define FIELD_GET(mask, reg)		(((reg) & (mask)) >> (__builtin_ctz(mask)))
> +#define GENMASK(h, l)			(((~0U) >> (31 - (h))) & (~0U << (l)))
> +
>  /* MCU WFDMA1 */
>  #define	MT_MCU_WFDMA1_BASE		0x3000
>  
> @@ -1401,6 +1406,12 @@
>  #define	PHY_TYPE_BIT_HT			(1U << 4)
>  #define	PHY_TYPE_BIT_VHT		(1U << 5)
>  #define	PHY_TYPE_BIT_HE			(1U << 6)
> +
> +/* P-RXV DW0 */
> +#define MT_PRXV_RCPI3			GENMASK(31, 24)
> +#define MT_PRXV_RCPI2			GENMASK(23, 16)
> +#define MT_PRXV_RCPI1			GENMASK(15, 8)
> +#define MT_PRXV_RCPI0			GENMASK(7, 0)
>  
>  #define	rssi_to_rcpi(rssi)		(2 * (rssi) + 220)
>  #define	rcpi_to_rssi(field, rxv)	((FIELD_GET(field, rxv) - 220) / 2)

Please do not introduce BIT, FIELD_GET and GENMASK and instead replace
them similar to how it is done in other places. You normally want a
XY_MASK and XY_SHIFT value.
I know that I have not converted all values yet in the header but I really
don't want those macros.

-- 
:wq Claudio