linux-kernel - [PATCH] spi: axi-spi-engine: don't emit XFER

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Message-ID: <20240723-spi-axi-spi-engine-opt-bpw-v1-1-2625ba4c4387@baylibre.com>
Date: Tue, 23 Jul 2024 13:36:47 -0500
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>
Cc: David Lechner <dlechner@...libre.com>,
	Michael Hennerich <michael.hennerich@...log.com>,
	Nuno Sá <nuno.sa@...log.com>,
	linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] spi: axi-spi-engine: don't emit XFER_BITS for empty xfer

This adds a check on xfer->len to avoid emitting an XFER_BITS
instruction for empty transfers in the AXI SPI Engine driver. This
avoids unnecessary delays caused by executing an instruction that has
no effect on the actual SPI transfer.

Signed-off-by: David Lechner <dlechner@...libre.com>
---
 drivers/spi/spi-axi-spi-engine.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-engine.c
index 447e5a962dee..cb3fdcbca2be 100644
--- a/drivers/spi/spi-axi-spi-engine.c
+++ b/drivers/spi/spi-axi-spi-engine.c
@@ -258,7 +258,7 @@ static void spi_engine_compile_message(struct spi_message *msg, bool dry,
 					clk_div - 1));
 		}
 
-		if (bits_per_word != xfer->bits_per_word) {
+		if (bits_per_word != xfer->bits_per_word && xfer->len) {
 			bits_per_word = xfer->bits_per_word;
 			spi_engine_program_add_cmd(p, dry,
 				SPI_ENGINE_CMD_WRITE(SPI_ENGINE_CMD_REG_XFER_BITS,

---
base-commit: 67e899c7df7dd8507ab61a2e71fe6c8299afd427
change-id: 20240723-spi-axi-spi-engine-opt-bpw-e801253aa43a