net: ipa: FLAVOR_0 register doesn't exist until IPA v3.5

The FLAVOR_0 version first appears in IPA v3.5, so avoid attempting
to read it for versions prior to that.

This register contains a concise definition of the number and
direction of endpoints supported by the hardware, and without it
we can't verify endpoint configuration in ipa_endpoint_config().
In this case, just indicate that any endpoint number is available
for use.

Originally proposed by AngeloGioacchino Del Regno.

Link: https://lore.kernel.org/netdev/20210211175015.200772-3-angelogioacchino.delregno@somainline.orgSigned-off-by: Alex Elder <elder@linaro.org>
Acked-by: AngeloGioacchino Del Regno
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipa/ipa_endpoint.c

@@ -1731,6 +1731,21 @@ int ipa_endpoint_config(struct ipa *ipa)
 	u32 max;
 	u32 val;
 
+	/* Prior to IPAv3.5, the FLAVOR_0 register was not supported.
+	 * Furthermore, the endpoints were not grouped such that TX
+	 * endpoint numbers started with 0 and RX endpoints had numbers
+	 * higher than all TX endpoints, so we can't do the simple
+	 * direction check used for newer hardware below.
+	 *
+	 * For hardware that doesn't support the FLAVOR_0 register,
+	 * just set the available mask to support any endpoint, and
+	 * assume the configuration is valid.
+	 */
+	if (ipa->version < IPA_VERSION_3_5) {
+		ipa->available = ~0;
+		return 0;
+	}
+
 	/* Find out about the endpoints supplied by the hardware, and ensure
 	 * the highest one doesn't exceed the number we support.
 	 */