ath9k: detect more kinds of invalid descriptors

If AR_CRCErr, AR_PHYErr, AR_DecryptCRCErr or AR_MichaelErr is indicated
in the rx status word, but AR_RxFrameOK is also set, the descriptor
contents are typically invalid. This can show up as a warning about
invalid MCS rates in a frame. Even with those checks in place, a
descriptor with invalid MCS rates can still sometimes make it through to
the driver (mostly on older hardware like AR91xx).

Detect such errors in the last descriptor of a frame and discard the
whole frame if present.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/mac.c b/drivers/net/wireless/ath/ath9k/mac.c
index 811007e..498fee0 100644
--- a/drivers/net/wireless/ath/ath9k/mac.c
+++ b/drivers/net/wireless/ath/ath9k/mac.c
@@ -615,6 +615,14 @@
 			rs->rs_status |= ATH9K_RXERR_DECRYPT;
 		else if (ads.ds_rxstatus8 & AR_MichaelErr)
 			rs->rs_status |= ATH9K_RXERR_MIC;
+	} else {
+		if (ads.ds_rxstatus8 &
+		    (AR_CRCErr | AR_PHYErr | AR_DecryptCRCErr | AR_MichaelErr))
+			rs->rs_status |= ATH9K_RXERR_CORRUPT_DESC;
+
+		/* Only up to MCS16 supported, everything above is invalid */
+		if (rs->rs_rate >= 0x90)
+			rs->rs_status |= ATH9K_RXERR_CORRUPT_DESC;
 	}
 
 	if (ads.ds_rxstatus8 & AR_KeyMiss)