[PATCH 2/3] spi: Parse the rx-sample-delay-ns peripheral property in the core

[Frieder Schrempf <frieder@fris.de>]

From: Frieder Schrempf <frieder.schrempf@kontron.de>

"rx-sample-delay-ns" is documented in spi-peripheral-props.yaml as a
generic SPI peripheral property, but the core never looks at it. Only
spi-dw reads it from the peripheral node as the binding describes, and
any other driver wanting to act on it would have to duplicate that.

Add spi_device.rx_sample_delay_ns and parse the property once, in
__spi_add_device(), which covers every way a device can be instantiated
and runs before ->setup().

Use device_property_read_u32() rather than adding this to
of_spi_parse_dt(). spi-dw already uses the fwnode accessor, so the
property works today on ACPI and software node platforms such as the
ones served by spi-dw-pci, and parsing it only in the device tree path
would quietly drop it there.

No functional change, since nothing reads the new field yet.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
---
 drivers/spi/spi.c       | 9 +++++++++
 include/linux/spi/spi.h | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 5b5b3bc5f0d8..9e3c24ed8f9f 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -929,6 +929,15 @@ static int __spi_add_device(struct spi_device *spi, struct spi_device *parent)
 		}
 	}
 
+	/*
+	 * Peripheral properties the core handles on behalf of controller
+	 * drivers are parsed here, rather than in the firmware specific
+	 * instantiation paths, so that device tree, ACPI and software nodes
+	 * are covered alike, and early enough for ->setup() to act on them.
+	 */
+	device_property_read_u32(&spi->dev, "rx-sample-delay-ns",
+				 &spi->rx_sample_delay_ns);
+
 	/*
 	 * Drivers may modify this initial i/o setup, but will
 	 * normally rely on the device being setup.  Devices
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 88d17fce02dc..fb4baa0d3398 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -169,6 +169,12 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
  * @cs_inactive: delay to be introduced by the controller after CS is
  *	deasserted. If @cs_change_delay is used from @spi_transfer, then the
  *	two delays will be added up.
+ * @rx_sample_delay_ns: Delay in nanoseconds by which the controller should
+ *	postpone sampling the incoming data, relative to the sampling point it
+ *	uses by default. Describes the board rather than the device, namely the
+ *	flight time of the clock and data signals between controller and
+ *	device, and comes from the "rx-sample-delay-ns" property. Zero when the
+ *	property is absent.
  * @chip_select: Array of physical chipselect, spi->chipselect[i] gives
  *	the corresponding physical CS for logical CS i.
  * @num_chipselect: Number of physical chipselects used.
@@ -235,6 +241,9 @@ struct spi_device {
 	struct spi_delay	cs_hold;
 	struct spi_delay	cs_inactive;
 
+	/* Additional delay before the incoming data is sampled, in ns */
+	u32			rx_sample_delay_ns;
+
 	u8			chip_select[SPI_DEVICE_CS_CNT_MAX];
 	u8			num_chipselect;
 

-- 
2.55.0