[PATCH net 4/5] net: ipa: header pad field only valid for AP->modem endpoint

From: Alex Elder <elder@linaro.org>
To: davem@davemloft.net, kuba@kernel.org
Cc: evgreen@chromium.org, subashab@codeaurora.org,
	cpratapa@codeaurora.org, bjorn.andersson@linaro.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net 4/5] net: ipa: header pad field only valid for AP->modem endpoint
Date: Wed, 10 Jun 2020 14:53:31 -0500	[thread overview]
Message-ID: <20200610195332.2612233-5-elder@linaro.org> (raw)
In-Reply-To: <20200610195332.2612233-1-elder@linaro.org>

Only QMAP endpoints should be configured to find a pad size field
within packet headers.  They are found in the first byte of the QMAP
header (and the hardware fills only the 6 bits in that byte that
constitute the pad_len field).

The RMNet driver assumes the pad_len field is valid for received
packets, so we want to ensure the pad_len field is filled in that
case.  That driver also assumes the length in the QMAP header
includes the pad bytes.

The RMNet driver does *not* pad the packets it sends, so the pad_len
field can be ignored.

Fix ipa_endpoint_init_hdr_ext() so it only marks the pad field
offset valid for QMAP RX endpoints, and in that case indicates
that the length field in the header includes the pad bytes.

Signed-off-by: Alex Elder <elder@linaro.org>
---
 drivers/net/ipa/ipa_endpoint.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
index 59313ced7036..b35e027003b3 100644
--- a/drivers/net/ipa/ipa_endpoint.c
+++ b/drivers/net/ipa/ipa_endpoint.c
@@ -467,7 +467,7 @@ void ipa_endpoint_init_hdr(struct ipa_endpoint *endpoint)
 			header_size += sizeof(struct rmnet_map_ul_csum_header);
 		val |= u32_encode_bits(header_size, HDR_LEN_FMASK);
 
-		/* Define how to fill mux_id in a received QMAP header */
+		/* Define how to fill fields in a received QMAP header */
 		if (!endpoint->toward_ipa) {
 			u32 off;	/* Field offset within header */
 
@@ -499,10 +499,21 @@ static void ipa_endpoint_init_hdr_ext(struct ipa_endpoint *endpoint)
 	u32 val = 0;
 
 	val |= HDR_ENDIANNESS_FMASK;		/* big endian */
-	val |= HDR_TOTAL_LEN_OR_PAD_VALID_FMASK;
-	/* HDR_TOTAL_LEN_OR_PAD is 0 (pad, not total_len) */
+
+	/* A QMAP header contains a 6 bit pad field at offset 0.  The RMNet
+	 * driver assumes this field is meaningful in packets it receives,
+	 * and assumes the header's payload length includes that padding.
+	 * The RMNet driver does *not* pad packets it sends, however, so
+	 * the pad field (although 0) should be ignored.
+	 */
+	if (endpoint->data->qmap && !endpoint->toward_ipa) {
+		val |= HDR_TOTAL_LEN_OR_PAD_VALID_FMASK;
+		/* HDR_TOTAL_LEN_OR_PAD is 0 (pad, not total_len) */
+		val |= HDR_PAYLOAD_LEN_INC_PADDING_FMASK;
+		/* HDR_TOTAL_LEN_OR_PAD_OFFSET is 0 */
+	}
+
 	/* HDR_PAYLOAD_LEN_INC_PADDING is 0 */
-	/* HDR_TOTAL_LEN_OR_PAD_OFFSET is 0 */
 	if (!endpoint->toward_ipa)
 		val |= u32_encode_bits(pad_align, HDR_PAD_TO_ALIGNMENT_FMASK);
 
-- 
2.25.1

