linux-kernel - [PATCH RFC v2 4/8] spi: add offload xfer flags

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Message-ID: <20240510-dlech-mainline-spi-engine-offload-2-v2-4-8707a870c435@baylibre.com>
Date: Fri, 10 May 2024 19:44:27 -0500
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Nuno Sá <nuno.sa@...log.com>
Cc: David Lechner <dlechner@...libre.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	David Jander <david@...tonic.nl>,
	Martin Sperl <kernel@...tin.sperl.org>,
	linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org
Subject: [PATCH RFC v2 4/8] spi: add offload xfer flags

Most configuration of SPI offloads is handles opaquely using the ID
handle that is passed to the various offload functions. However, there
are some offload features that need to be controller on a per transfer
basis.

This patch adds a flags field to the spi_transfer structure to allow
specifying such features. The first feature to be added is the ability
to stream data to/from a hardware sink/source rather than using a tx or
rx buffer. Additional flags can be added in the future as needed.

A flags field is also added to the controller struct for controllers to
indicate which flags are supported. This allows for generic checking of
offload capabilities during __spi_validate() so that each controller
doesn't have to provide their own validation.

Signed-off-by: David Lechner <dlechner@...libre.com>
---

v2 changes:

This is also split out from "spi: add core support for controllers with
offload capabilities".

In the previous version, we were using (void *)-1 as a sentinel value
that could be assigned, e.g. to rx_buf. But this was naive since there
is core code that would try to dereference this pointer. So instead,
we've added a new flags field to the spi_transfer structure for this
sort of thing. This also has the advantage of being able to be used in
the future for other arbitrary features.
---
 drivers/spi/spi.c       | 10 ++++++++++
 include/linux/spi/spi.h | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9ad7b04c26a6..4d34ccf91fd4 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -4189,6 +4189,16 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 
 		if (_spi_xfer_word_delay_update(xfer, spi))
 			return -EINVAL;
+
+		/* make sure controller supports required offload features */
+		if (xfer->offload_flags) {
+			if (!message->offload)
+				return -EINVAL;
+
+			if ((xfer->offload_flags & ctlr->offload_xfer_flags)
+			    != xfer->offload_flags)
+				return -EINVAL;
+		}
 	}
 
 	message->status = -EINPROGRESS;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index ec8d875d31ff..42c39c17ba5a 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -501,6 +501,8 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  *	     This field is optional and should only be implemented if the
  *	     controller has native support for memory like operations.
  * @mem_caps: controller capabilities for the handling of memory operations.
+ * @offload_xfer_flags: flags supported by this controller for offloading
+ *	transfers. See struct spi_transfer for the list of flags.
  * @offload_ops: operations for controllers with offload support.
  * @unprepare_message: undo any work done by prepare_message().
  * @slave_abort: abort the ongoing transfer request on an SPI slave controller
@@ -751,6 +753,7 @@ struct spi_controller {
 	const struct spi_controller_mem_caps *mem_caps;
 
 	/* Operations for controllers with offload support. */
+	unsigned int offload_xfer_flags;
 	const struct spi_controller_offload_ops *offload_ops;
 
 	/* GPIO chip select */
@@ -991,6 +994,7 @@ struct spi_res {
  * @transfer_list: transfers are sequenced through @spi_message.transfers
  * @tx_sg: Scatterlist for transmit, currently not for client use
  * @rx_sg: Scatterlist for receive, currently not for client use
+ * @offload_flags: flags for xfers that use special hardware offload features
  * @ptp_sts_word_pre: The word (subject to bits_per_word semantics) offset
  *	within @tx_buf for which the SPI device is requesting that the time
  *	snapshot for this transfer begins. Upon completing the SPI transfer,
@@ -1107,6 +1111,12 @@ struct spi_transfer {
 
 	u32		effective_speed_hz;
 
+	unsigned int	offload_flags;
+/* this is write xfer but TX uses external data stream rather than tx_buf */
+#define SPI_OFFLOAD_XFER_TX_STREAM	BIT(0)
+/* this is read xfer but RX uses external data stream rather than rx_buf */
+#define SPI_OFFLOAD_XFER_RX_STREAM	BIT(1)
+
 	unsigned int	ptp_sts_word_pre;
 	unsigned int	ptp_sts_word_post;
 

-- 
2.43.2