linux-kernel - [PATCH v1 2/2] spi: fsl-spi: Implement trailing clock mode

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Date:   Sun, 27 Feb 2022 11:00:35 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Mark Brown <broonie@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Pratyush Yadav <p.yadav@...com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: [PATCH v1 2/2] spi: fsl-spi: Implement trailing clock mode

In order to support IDT 801034 QUAD PCM CODEC, implement the
trailing clock mode.

On fsl SPI, the minimum we can implement is a 4 bits shot.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 drivers/spi/spi-fsl-lib.c |  2 +-
 drivers/spi/spi-fsl-spi.c | 15 +++++++++++++--
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-fsl-lib.c b/drivers/spi/spi-fsl-lib.c
index 76e1192eb025..a13f3b4db55f 100644
--- a/drivers/spi/spi-fsl-lib.c
+++ b/drivers/spi/spi-fsl-lib.c
@@ -88,7 +88,7 @@ void mpc8xxx_spi_probe(struct device *dev, struct resource *mem,
 
 	/* the spi->mode bits understood by this driver: */
 	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH
-			| SPI_LSB_FIRST | SPI_LOOP;
+			| SPI_LSB_FIRST | SPI_LOOP | SPI_TRAILING;
 
 	master->dev.of_node = dev->of_node;
 
diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
index bdf94cc7be1a..6a52955d9051 100644
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -424,13 +424,24 @@ static int fsl_spi_do_one_msg(struct spi_master *master,
 		}
 	}
 
-	m->status = status;
-
 	if (status || !cs_change) {
 		ndelay(nsecs);
 		fsl_spi_chipselect(spi, BITBANG_CS_INACTIVE);
 	}
 
+	if (!status && spi->mode & SPI_TRAILING) {
+		struct spi_transfer t = {
+			.len = 1,
+			.tx_buf = "",
+			.bits_per_word = 4
+		};
+
+		status = fsl_spi_setup_transfer(spi, &t);
+		if (!status)
+			status = fsl_spi_bufs(spi, &t, 0);
+	}
+	m->status = status;
+
 	fsl_spi_setup_transfer(spi, NULL);
 	spi_finalize_current_message(master);
 	return 0;
-- 
2.34.1