[PATCH] spi: move split xfers for CS_WORD emulation

[PATCH] spi: move split xfers for CS_WORD emulation

[David Lechner]

This moves splitting transfers for CS_WORD software emulation to the
same place where we split transfers for controller-specific reasons.

This fixes a few subtle bugs.

The calculation for maxsize was wrong for bit sizes between 17 and 24.
This is fixed by making use of spi_split_transfers_maxwords() which
already has the correct calculation.

Also, since this indirectly calls spi_res_alloc(), to avoid leaking
resources, spi_finalize_current_message() would need to be called
on all error paths in __spi_validate() and callers of __spi_validate()
would need to do the same. This is fixed by moving the call to
__spi_pump_transfer_message() where it is already splitting transfers
for other reasons and correctly releases resources in the subsequent
error paths.

Fixes: cbaa62e0094a ("spi: add software implementation for SPI_CS_WORD")
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 drivers/spi/spi.c | 63 +++++++++++++++++++++++------------------------
 1 file changed, 31 insertions(+), 32 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 53c25a351dab..a8b8474abc74 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1747,13 +1747,37 @@ static int __spi_pump_transfer_message(struct spi_controller *ctlr,
 
 	trace_spi_message_start(msg);
 
-	ret = spi_split_transfers_maxsize(ctlr, msg,
-					  spi_max_transfer_size(msg->spi),
-					  GFP_KERNEL | GFP_DMA);
-	if (ret) {
-		msg->status = ret;
-		spi_finalize_current_message(ctlr);
-		return ret;
+	/*
+	 * If an SPI controller does not support toggling the CS line on each
+	 * transfer (indicated by the SPI_CS_WORD flag) or we are using a GPIO
+	 * for the CS line, we can emulate the CS-per-word hardware function by
+	 * splitting transfers into one-word transfers and ensuring that
+	 * cs_change is set for each transfer.
+	 */
+	if ((msg->spi->mode & SPI_CS_WORD) && (!(ctlr->mode_bits & SPI_CS_WORD) ||
+					       spi_is_csgpiod(msg->spi))) {
+		ret = spi_split_transfers_maxwords(ctlr, msg, 1, GFP_KERNEL);
+		if (ret) {
+			msg->status = ret;
+			spi_finalize_current_message(ctlr);
+			return ret;
+		}
+
+		list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+			/* Don't change cs_change on the last entry in the list */
+			if (list_is_last(&xfer->transfer_list, &msg->transfers))
+				break;
+			xfer->cs_change = 1;
+		}
+	} else {
+		ret = spi_split_transfers_maxsize(ctlr, msg,
+						  spi_max_transfer_size(msg->spi),
+						  GFP_KERNEL | GFP_DMA);
+		if (ret) {
+			msg->status = ret;
+			spi_finalize_current_message(ctlr);
+			return ret;
+		}
 	}
 
 	if (ctlr->prepare_message) {
@@ -4065,31 +4089,6 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 
 	message->spi = spi;
 
-	/*
-	 * If an SPI controller does not support toggling the CS line on each
-	 * transfer (indicated by the SPI_CS_WORD flag) or we are using a GPIO
-	 * for the CS line, we can emulate the CS-per-word hardware function by
-	 * splitting transfers into one-word transfers and ensuring that
-	 * cs_change is set for each transfer.
-	 */
-	if ((spi->mode & SPI_CS_WORD) && (!(ctlr->mode_bits & SPI_CS_WORD) ||
-					  spi_is_csgpiod(spi))) {
-		size_t maxsize = BITS_TO_BYTES(spi->bits_per_word);
-		int ret;
-
-		ret = spi_split_transfers_maxsize(ctlr, message, maxsize,
-						  GFP_KERNEL);
-		if (ret)
-			return ret;
-
-		list_for_each_entry(xfer, &message->transfers, transfer_list) {
-			/* Don't change cs_change on the last entry in the list */
-			if (list_is_last(&xfer->transfer_list, &message->transfers))
-				break;
-			xfer->cs_change = 1;
-		}
-	}
-
 	/*
 	 * Half-duplex links include original MicroWire, and ones with
 	 * only one data pin like SPI_3WIRE (switches direction) or where
-- 
2.43.0

Re: [PATCH] spi: move split xfers for CS_WORD emulation

[Mark Brown]

On Fri, 26 Jan 2024 15:23:57 -0600, David Lechner wrote:
> This moves splitting transfers for CS_WORD software emulation to the
> same place where we split transfers for controller-specific reasons.
> 
> This fixes a few subtle bugs.
> 
> The calculation for maxsize was wrong for bit sizes between 17 and 24.
> This is fixed by making use of spi_split_transfers_maxwords() which
> already has the correct calculation.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: move split xfers for CS_WORD emulation
      commit: c8bec3355f08ddb887d5c13b7095dfa79e6db108

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark