fpga manager: xilinx-spi: check INIT_B pin during write_init

The INIT_B pin reports the status during startup and after the end of the
programming process. However the current driver completely ignores it.

Check the pin status during startup to make sure programming is never
started too early and also to detect any hardware issues in the FPGA
connection.

This is optional for backward compatibility. If INIT_B is not passed by
device tree, just fallback to the old udelays.
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/xilinx-spi.c

@@ -23,6 +23,7 @@
 struct xilinx_spi_conf {
 	struct spi_device *spi;
 	struct gpio_desc *prog_b;
+	struct gpio_desc *init_b;
 	struct gpio_desc *done;
 };
 
@@ -36,11 +37,45 @@ static enum fpga_mgr_states xilinx_spi_state(struct fpga_manager *mgr)
 	return FPGA_MGR_STATE_UNKNOWN;
 }
 
+/**
+ * wait_for_init_b - wait for the INIT_B pin to have a given state, or wait
+ * a given delay if the pin is unavailable
+ *
+ * @mgr:        The FPGA manager object
+ * @value:      Value INIT_B to wait for (1 = asserted = low)
+ * @alt_udelay: Delay to wait if the INIT_B GPIO is not available
+ *
+ * Returns 0 when the INIT_B GPIO reached the given state or -ETIMEDOUT if
+ * too much time passed waiting for that. If no INIT_B GPIO is available
+ * then always return 0.
+ */
+static int wait_for_init_b(struct fpga_manager *mgr, int value,
+			   unsigned long alt_udelay)
+{
+	struct xilinx_spi_conf *conf = mgr->priv;
+	unsigned long timeout = jiffies + msecs_to_jiffies(1000);
+
+	if (conf->init_b) {
+		while (time_before(jiffies, timeout)) {
+			/* dump_state(conf, "wait for init_d .."); */
+			if (gpiod_get_value(conf->init_b) == value)
+				return 0;
+			usleep_range(100, 400);
+		}
+		return -ETIMEDOUT;
+	}
+
+	udelay(alt_udelay);
+
+	return 0;
+}
+
 static int xilinx_spi_write_init(struct fpga_manager *mgr,
 				 struct fpga_image_info *info,
 				 const char *buf, size_t count)
 {
 	struct xilinx_spi_conf *conf = mgr->priv;
+	int err;
 
 	if (info->flags & FPGA_MGR_PARTIAL_RECONFIG) {
 		dev_err(&mgr->dev, "Partial reconfiguration not supported.\n");
@@ -49,10 +84,21 @@ static int xilinx_spi_write_init(struct fpga_manager *mgr,
 
 	gpiod_set_value(conf->prog_b, 1);
 
-	udelay(1); /* min is 500 ns */
+	err = wait_for_init_b(mgr, 1, 1); /* min is 500 ns */
+	if (err) {
+		dev_err(&mgr->dev, "INIT_B pin did not go low\n");
+		gpiod_set_value(conf->prog_b, 0);
+		return err;
+	}
 
 	gpiod_set_value(conf->prog_b, 0);
 
+	err = wait_for_init_b(mgr, 0, 0);
+	if (err) {
+		dev_err(&mgr->dev, "INIT_B pin did not go high\n");
+		return err;
+	}
+
 	if (gpiod_get_value(conf->done)) {
 		dev_err(&mgr->dev, "Unexpected DONE pin state...\n");
 		return -EIO;
@@ -154,6 +200,13 @@ static int xilinx_spi_probe(struct spi_device *spi)
 		return PTR_ERR(conf->prog_b);
 	}
 
+	conf->init_b = devm_gpiod_get_optional(&spi->dev, "init-b", GPIOD_IN);
+	if (IS_ERR(conf->init_b)) {
+		dev_err(&spi->dev, "Failed to get INIT_B gpio: %ld\n",
+			PTR_ERR(conf->init_b));
+		return PTR_ERR(conf->init_b);
+	}
+
 	conf->done = devm_gpiod_get(&spi->dev, "done", GPIOD_IN);
 	if (IS_ERR(conf->done)) {
 		dev_err(&spi->dev, "Failed to get DONE gpio: %ld\n",