[PATCH] net: ipa: compute proper aggregation limit

[Alex Elder <elder@linaro.org>]

commit c5794097b269f15961ed78f7f27b50e51766dec9 upstream.

The aggregation byte limit for an endpoint is currently computed
based on the endpoint's receive buffer size.

However, some bytes at the front of each receive buffer are reserved
on the assumption that--as with SKBs--it might be useful to insert
data (such as headers) before what lands in the buffer.

The aggregation byte limit currently doesn't take into account that
reserved space, and as a result, aggregation could require space
past that which is available in the buffer.

Fix this by reducing the size used to compute the aggregation byte
limit by the NET_SKB_PAD offset reserved for each receive buffer.

Cc: <stable@vger.kernel.org>    # 5.15.x
Cc: <stable@vger.kernel.org>    # 5.17.x
Fixes: 84f9bd12d46db ("soc: qcom: ipa: IPA endpoints");
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
The original commit doesn't cherry-pick cleanly to v5.15.44 or v5.17.12  -Alex

 drivers/net/ipa/ipa_endpoint.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
index 87e42db1b61e6..477eb4051bed7 100644
--- a/drivers/net/ipa/ipa_endpoint.c
+++ b/drivers/net/ipa/ipa_endpoint.c
@@ -722,13 +722,15 @@ static void ipa_endpoint_init_aggr(struct ipa_endpoint *endpoint)
 
 	if (endpoint->data->aggregation) {
 		if (!endpoint->toward_ipa) {
+			u32 buffer_size;
 			bool close_eof;
 			u32 limit;
 
 			val |= u32_encode_bits(IPA_ENABLE_AGGR, AGGR_EN_FMASK);
 			val |= u32_encode_bits(IPA_GENERIC, AGGR_TYPE_FMASK);
 
-			limit = ipa_aggr_size_kb(IPA_RX_BUFFER_SIZE);
+			buffer_size = IPA_RX_BUFFER_SIZE - NET_SKB_PAD;
+			limit = ipa_aggr_size_kb(buffer_size);
 			val |= aggr_byte_limit_encoded(version, limit);
 
 			limit = IPA_AGGR_TIME_LIMIT;
-- 
2.32.0