[PATCH] wifi: brcmfmac: disable TX beamforming on BCM4364

[Andre Eikmeyer <dev@deq.rocks>]

With "txbf" enabled, the BCM4364 firmware (9.30.514.0.32.5.94, as shipped
by Apple for the MacBookPro15,1) transmits a single beamformed spatial
stream (nrate VHT MCS9 NSS1 TXBF) towards a two stream AP. With "txbf"
cleared it picks two streams (VHT MCS9 NSS2) on its own. The firmware
enables "txbf" by default, so the driver has to clear it.

Measured with iperf3 against a wired server on the same AP:

  0.5 m from the AP, -36 dBm:  351 -> 623 Mbit/s uplink
  -70 dBm:                      96-130 -> 149-175 Mbit/s uplink

Downlink and latency are unchanged. I did not notice any refression.

Tested-by: Yossef Osman <Yossef.Osman@proton.me>
Tested-by: Aditya Garg <aditya.garg@linux.dev>
Signed-off-by: Andre Eikmeyer <dev@deq.rocks>
---
The KaiT2en community runs this patch with its kernels, no regression
was reported.

 .../net/wireless/broadcom/brcm80211/brcmfmac/common.c    | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c
index b6027d83e6a..b09abd5fee3 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c
@@ -10,6 +10,7 @@
 #include <linux/firmware.h>
 #include <brcmu_wifi.h>
 #include <brcmu_utils.h>
+#include <brcm_hw_ids.h>
 #include "core.h"
 #include "bus.h"
 #include "debug.h"
@@ -450,8 +451,12 @@ int brcmf_c_preinit_dcmds(struct brcmf_if *ifp)
 		goto done;
 	}
 
-	/* Enable tx beamforming, errors can be ignored (not supported) */
-	(void)brcmf_fil_iovar_int_set(ifp, "txbf", 1);
+	/* Enable tx beamforming, errors can be ignored (not supported).
+	 * BCM4364 firmware enables it by default and then transmits a single
+	 * beamformed stream instead of two, halving its uplink throughput.
+	 */
+	(void)brcmf_fil_iovar_int_set(ifp, "txbf",
+				      drvr->bus_if->chip != BRCM_CC_4364_CHIP_ID);
 done:
 	return err;
 }

base-commit: 991a73f4909f1348ffb4b38765cdb522a775e4c2