[PATCH v2 3/5] spi: introduce SPI ancillary device with lanes

[Jonathan Santos <Jonathan.Santos@analog.com>]

The existing spi_new_ancillary_device() creates an ancillary SPI device
but does not consider the parent's lane map. In multi-device setups where
each sub-device's chip-select is bound to a dedicated data lane, there is
no way to bind an ancillary device to an arbitrary lane index.

Introduce spi_new_ancillary_device_with_lane() and
devm_spi_new_ancillary_device_with_lane(), which accept rx_lane_idx and
tx_lane_idx parameters to select a specific lane from the parent's
rx_lane_map and tx_lane_map respectively. The resulting ancillary device
is registered with a single RX and TX lane, keeping it independent from
the other sub-devices sharing the same controller.

Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
---
Changes in v2:
* New patch.
---
 drivers/spi/spi.c       | 102 ++++++++++++++++++++++++++++++++++++++++
 include/linux/spi/spi.h |   8 ++++
 2 files changed, 110 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 61423aee1525..d41c9392c04e 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2749,6 +2749,72 @@ struct spi_device *spi_new_ancillary_device(struct spi_device *spi,
 }
 EXPORT_SYMBOL_GPL(spi_new_ancillary_device);
 
+/**
+ * spi_new_ancillary_device_with_lane() - Register ancillary SPI device bound to specific lane
+ * @spi:          Pointer to the main SPI device registering the ancillary device
+ * @chip_select:  Chip Select of the ancillary device
+ * @rx_lane_idx:  Lane index within the parent's rx_lane_map
+ * @tx_lane_idx:  Lane index within the parent's tx_lane_map
+ *
+ * Like spi_new_ancillary_device(), but additionally binds the ancillary device
+ * to a single lane from the parent's lane map. Use this in multi-device setups
+ * where each sub-device is physically wired to a dedicated CS and a dedicated
+ * data lane.
+ *
+ * This may only be called from main SPI device's probe routine.
+ *
+ * Return: Pointer to new ancillary device on success; ERR_PTR on failure
+ */
+struct spi_device *spi_new_ancillary_device_with_lane(struct spi_device *spi,
+						      u8 chip_select,
+						      unsigned int rx_lane_idx,
+						      unsigned int tx_lane_idx)
+{
+	struct spi_controller *ctlr = spi->controller;
+	struct spi_device *ancillary;
+	int rc;
+
+	ancillary = spi_alloc_device(ctlr);
+	if (!ancillary) {
+		rc = -ENOMEM;
+		goto err_out;
+	}
+
+	strscpy(ancillary->modalias, "dummy", sizeof(ancillary->modalias));
+
+	spi_set_chipselect(ancillary, 0, chip_select);
+
+	ancillary->max_speed_hz = spi->max_speed_hz;
+	ancillary->mode = spi->mode;
+	ancillary->cs_index_mask = BIT(0);
+
+	if (rx_lane_idx >= spi->num_rx_lanes || tx_lane_idx >= spi->num_tx_lanes) {
+		rc = -EINVAL;
+		goto err_out;
+	}
+
+	ancillary->rx_lane_map[0] = spi->rx_lane_map[rx_lane_idx];
+	ancillary->num_rx_lanes = 1;
+	ancillary->tx_lane_map[0] = spi->tx_lane_map[tx_lane_idx];
+	ancillary->num_tx_lanes = 1;
+
+	WARN_ON(!mutex_is_locked(&ctlr->add_lock));
+
+	/* Register the new device, passing the parent to skip CS conflict check */
+	rc = __spi_add_device(ancillary, spi);
+	if (rc) {
+		dev_err(&spi->dev, "failed to register ancillary device\n");
+		goto err_out;
+	}
+
+	return ancillary;
+
+err_out:
+	spi_dev_put(ancillary);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(spi_new_ancillary_device_with_lane);
+
 static void devm_spi_unregister_device(void *spi)
 {
 	spi_unregister_device(spi);
@@ -2789,6 +2855,42 @@ struct spi_device *devm_spi_new_ancillary_device(struct spi_device *spi,
 }
 EXPORT_SYMBOL_GPL(devm_spi_new_ancillary_device);
 
+/**
+ * devm_spi_new_ancillary_device_with_lane() - Register managed ancillary SPI device bound to a lane
+ * @spi:         Pointer to the main SPI device registering the ancillary device
+ * @chip_select: Chip Select of the ancillary device
+ * @rx_lane_idx: Per-device lane index within the parent's rx_lane_map
+ * @tx_lane_idx: Per-device lane index within the parent's tx_lane_map
+ *
+ * Managed version of spi_new_ancillary_device_with_lane(). The ancillary device
+ * will be unregistered automatically when the parent SPI device is unregistered.
+ *
+ * This may only be called from main SPI device's probe routine.
+ *
+ * Return: Pointer to new ancillary device on success; ERR_PTR on failure
+ */
+struct spi_device *devm_spi_new_ancillary_device_with_lane(struct spi_device *spi,
+							   u8 chip_select,
+							   unsigned int rx_lane_idx,
+							   unsigned int tx_lane_idx)
+{
+	struct spi_device *ancillary;
+	int ret;
+
+	ancillary = spi_new_ancillary_device_with_lane(spi, chip_select,
+						       rx_lane_idx, tx_lane_idx);
+	if (IS_ERR(ancillary))
+		return ancillary;
+
+	ret = devm_add_action_or_reset(&spi->dev, devm_spi_unregister_device,
+				       ancillary);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return ancillary;
+}
+EXPORT_SYMBOL_GPL(devm_spi_new_ancillary_device_with_lane);
+
 #ifdef CONFIG_ACPI
 struct acpi_spi_lookup {
 	struct spi_controller 	*ctlr;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 4c285d3ede1d..91c9e2d2e7e3 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -385,6 +385,14 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
 
 extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 chip_select);
 extern struct spi_device *devm_spi_new_ancillary_device(struct spi_device *spi, u8 chip_select);
+extern struct spi_device *spi_new_ancillary_device_with_lane(struct spi_device *spi,
+							     u8 chip_select,
+							     unsigned int rx_lane_idx,
+							     unsigned int tx_lane_idx);
+extern struct spi_device *devm_spi_new_ancillary_device_with_lane(struct spi_device *spi,
+								  u8 chip_select,
+								  unsigned int rx_lane_idx,
+								  unsigned int tx_lane_idx);
 
 /* Use a define to avoid include chaining to get THIS_MODULE */
 #define spi_register_driver(driver) \
-- 
2.34.1