sahara: Deal with QUD discarding the HELLO request

When running on modern platforms it's observed that the Qualcomm USB
Drivers will discard the HELLO request from the device, so we're forced
to speculatively send a HELLO response on an initial timeout.

In the event that the device is already in Firehose mode (from a
previous --skip-reset run), the HELLO response will result in a XML
parse error in the programmer, for which we catch the "<?xml" prefix and
return to Firehose mode.

Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>

Author: quic-bjorande

sahara.c

@@ -124,10 +124,23 @@ static void sahara_send_reset(struct qdl_device *qdl)
 	qdl_write(qdl, &resp, resp.length, SAHARA_CMD_TIMEOUT_MS);
 }
 
-static int sahara_hello(struct qdl_device *qdl, struct sahara_pkt *pkt)
+static int sahara_send_hello_resp(struct qdl_device *qdl, unsigned int mode)
 {
 	struct sahara_pkt resp = {};
 
+	resp.cmd = SAHARA_HELLO_RESP_CMD;
+	resp.length = SAHARA_HELLO_LENGTH;
+	resp.hello_resp.version = SAHARA_VERSION;
+	resp.hello_resp.compatible = 1;
+	resp.hello_resp.status = SAHARA_SUCCESS;
+	resp.hello_resp.mode = mode;
+
+	qdl_write(qdl, &resp, resp.length, SAHARA_CMD_TIMEOUT_MS);
+	return 0;
+}
+
+static int sahara_hello(struct qdl_device *qdl, struct sahara_pkt *pkt)
+{
 	if (pkt->length != SAHARA_HELLO_LENGTH) {
 		ux_err("unexpected HELLO packet length %u\n", pkt->length);
 		sahara_send_reset(qdl);
@@ -137,15 +150,7 @@ static int sahara_hello(struct qdl_device *qdl, struct sahara_pkt *pkt)
 	ux_debug("HELLO version: 0x%x compatible: 0x%x max_len: %d mode: %d\n",
 		 pkt->hello_req.version, pkt->hello_req.compatible, pkt->hello_req.max_len, pkt->hello_req.mode);
 
-	resp.cmd = SAHARA_HELLO_RESP_CMD;
-	resp.length = SAHARA_HELLO_LENGTH;
-	resp.hello_resp.version = SAHARA_VERSION;
-	resp.hello_resp.compatible = 1;
-	resp.hello_resp.status = SAHARA_SUCCESS;
-	resp.hello_resp.mode = pkt->hello_req.mode;
-
-	qdl_write(qdl, &resp, resp.length, SAHARA_CMD_TIMEOUT_MS);
-	return 0;
+	return sahara_send_hello_resp(qdl, pkt->hello_req.mode);
 }
 
 static int sahara_read(struct qdl_device *qdl, struct sahara_pkt *pkt,
@@ -538,6 +543,19 @@ int sahara_run(struct qdl_device *qdl, const struct sahara_image *images,
 		n = qdl_read(qdl, buf, sizeof(buf), SAHARA_CMD_TIMEOUT_MS);
 		if (n < 0) {
 			if (first_read && detect_firehose && n == -ETIMEDOUT) {
+				/*
+				 * The QUD driver will eat the HELLO request on
+				 * many modern targets, so send an unsolicited
+				 * HELLO response.
+				 * If the device is already in Firehose mode,
+				 * the programmer will fail to parse the "XML"
+				 * message and report an error, which will
+				 * trigger below detection of a <?xml response.
+				 */
+				if (qdl->dev_type == QDL_DEVICE_QUD || qdl->dev_type == QDL_DEVICE_AUTO) {
+					sahara_send_hello_resp(qdl, 0);
+					continue;
+				}
 				ux_info("no Sahara HELLO received; assuming Firehose programmer is already running\n");
 				return 0;
 			}