[PATCH v2 mvebu + mvebu/dt64 3/6] firmware: turris-mox-rwtm: fail probing when firmware does not support hwrng

[Pali Rohár]

When Marvell's rWTM firmware, which does not support the GET_RANDOM
command, is used, kernel prints an error message
  hwrng: no data available
every 10 seconds.

Fail probing of this driver if the rWTM firmware does not support the
GET_RANDOM command.

This makes it possible to put this driver's compatible into generic
armada-37xx device tree, to be available for other Armada 3720 devices
besides Turris MOX. If they use the rWTM firmware from CZ.NIC, they will
have HWRNG available, and if not, the driver won't be complaining.

Signed-off-by: Pali Rohár <pali at kernel.org>
Fixes: 389711b37493 ("firmware: Add Turris Mox rWTM firmware driver")
Signed-off-by: Marek Behún <kabel at kernel.org>
---
 drivers/firmware/turris-mox-rwtm.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/firmware/turris-mox-rwtm.c b/drivers/firmware/turris-mox-rwtm.c
index d7e3489e4bf2..3ef9687dddca 100644
--- a/drivers/firmware/turris-mox-rwtm.c
+++ b/drivers/firmware/turris-mox-rwtm.c
@@ -260,6 +260,27 @@ static int mox_get_board_info(struct mox_rwtm *rwtm)
 	return 0;
 }
 
+static int check_get_random_support(struct mox_rwtm *rwtm)
+{
+	struct armada_37xx_rwtm_tx_msg msg;
+	int ret;
+
+	msg.command = MBOX_CMD_GET_RANDOM;
+	msg.args[0] = 1;
+	msg.args[1] = rwtm->buf_phys;
+	msg.args[2] = 4;
+
+	ret = mbox_send_message(rwtm->mbox, &msg);
+	if (ret < 0)
+		return ret;
+
+	ret = wait_for_completion_timeout(&rwtm->cmd_done, HZ / 2);
+	if (ret < 0)
+		return ret;
+
+	return mox_get_status(MBOX_CMD_GET_RANDOM, rwtm->reply.retval);
+}
+
 static int mox_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 {
 	struct mox_rwtm *rwtm = (struct mox_rwtm *) rng->priv;
@@ -497,6 +518,13 @@ static int turris_mox_rwtm_probe(struct platform_device *pdev)
 	if (ret < 0)
 		dev_warn(dev, "Cannot read board information: %i\n", ret);
 
+	ret = check_get_random_support(rwtm);
+	if (ret < 0) {
+		dev_notice(dev,
+			   "Firmware does not support the GET_RANDOM command\n");
+		goto free_channel;
+	}
+
 	rwtm->hwrng.name = DRIVER_NAME "_hwrng";
 	rwtm->hwrng.read = mox_hwrng_read;
 	rwtm->hwrng.priv = (unsigned long) rwtm;
-- 
2.20.1