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From:   greearb@candelatech.com
To:     linux-wireless@vger.kernel.org
Cc:     Ben Greear <greearb@candelatech.com>
Subject: [PATCH 01/15] mt76: mt7915:  add comments about rx descriptor parsing
Date:   Wed, 11 Aug 2021 14:44:25 -0700
Message-Id: <20210811214439.17458-2-greearb@candelatech.com>
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From: Ben Greear <greearb@candelatech.com>

This is a tricky beast to understand, so add some notes for
next time someone is looking at this code and trying to compare
against documents.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 .../net/wireless/mediatek/mt76/mt7915/mac.c   | 23 +++++++++++++++----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
index 2c5b47766949..d836c665ddaf 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
@@ -410,6 +410,7 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 	__le32 *rxd = (__le32 *)skb->data;
 	__le32 *rxv = NULL;
 	u32 mode = 0;
+	/* table "PP -> HOST / X-CPU"  RX Format */
 	u32 rxd0 = le32_to_cpu(rxd[0]);
 	u32 rxd1 = le32_to_cpu(rxd[1]);
 	u32 rxd2 = le32_to_cpu(rxd[2]);
@@ -489,7 +490,7 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 
 	rxd += 6;
 	if (rxd1 & MT_RXD1_NORMAL_GROUP_4) {
-		u32 v0 = le32_to_cpu(rxd[0]);
+		u32 v0 = le32_to_cpu(rxd[0]); /* DW6 */
 		u32 v2 = le32_to_cpu(rxd[2]);
 
 		fc = cpu_to_le16(FIELD_GET(MT_RXD6_FRAME_CONTROL, v0));
@@ -502,6 +503,7 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 	}
 
 	if (rxd1 & MT_RXD1_NORMAL_GROUP_1) {
+		/* DW10, assuming Group-4 enabled */
 		u8 *data = (u8 *)rxd;
 
 		if (status->flag & RX_FLAG_DECRYPTED) {
@@ -533,6 +535,7 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 	}
 
 	if (rxd1 & MT_RXD1_NORMAL_GROUP_2) {
+		/* DW14, assuming group-1,4 */
 		status->timestamp = le32_to_cpu(rxd[0]);
 		status->flag |= RX_FLAG_MACTIME_START;
 
@@ -558,18 +561,22 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 	if (rxd1 & MT_RXD1_NORMAL_GROUP_3) {
 		u32 v0, v1, v2;
 
-		rxv = rxd;
+		rxv = rxd; /* DW16 assuming group 1,2,3,4 */
 		rxd += 2;
 		if ((u8 *)rxd - skb->data >= skb->len)
 			return -EINVAL;
 
-		v0 = le32_to_cpu(rxv[0]);
+		v0 = le32_to_cpu(rxv[0]);  /* DW16, P-VEC1 31:0 */
+		/* DW17, RX_RCPI copied over P-VEC 64:32 Per RX Format doc. */
 		v1 = le32_to_cpu(rxv[1]);
-		v2 = le32_to_cpu(rxv[2]);
+		v2 = le32_to_cpu(rxv[2]); /* first DW of group-5, C-RXV */
 
 		if (v0 & MT_PRXV_HT_AD_CODE)
 			status->enc_flags |= RX_ENC_FLAG_LDPC;
 
+		/* TODO:  When group-5 is enabled, use nss (and stbc) to
+		 * calculate chains properly for this particular skb.
+		 */
 		status->chains = mphy->antenna_mask;
 		status->chain_signal[0] = to_rssi(MT_PRXV_RCPI0, v1);
 		status->chain_signal[1] = to_rssi(MT_PRXV_RCPI1, v1);
@@ -581,12 +588,18 @@ mt7915_mac_fill_rx(struct mt7915_dev *dev, struct sk_buff *skb)
 			if (!(status->chains & BIT(i)))
 				continue;
 
+			/* TODO:  Use db sum logic instead of max. */
 			status->signal = max(status->signal,
 					     status->chain_signal[i]);
 		}
 
-		/* RXD Group 5 - C-RXV */
+		/* RXD Group 5 - C-RXV.
+		 * Group 5 Not currently enabled for 7915 except in
+		 * monitor mode.
+		 *   See MT_DMA_DCR0_RXD_G5_EN
+		 */
 		if (rxd1 & MT_RXD1_NORMAL_GROUP_5) {
+			/* See RXV document ... */
 			u8 stbc = FIELD_GET(MT_CRXV_HT_STBC, v2);
 			u8 gi = FIELD_GET(MT_CRXV_HT_SHORT_GI, v2);
 			bool cck = false;
-- 
2.20.1