linux-kernel - [PATCH v2 2/2] spi: fsl-spi: Implement trailing bits

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Date:   Mon, 28 Feb 2022 16:15:46 +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 v2 2/2] spi: fsl-spi: Implement trailing bits

In order to support IDT 801034 QUAD PCM CODEC, implement
trailing clock for the amount of requested bits.

On fsl SPI, the minimum we can implement is a 4 bits shot.
If the requested number is greated than 8, use 16.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 drivers/spi/spi-fsl-spi.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
index bdf94cc7be1a..aefaea439672 100644
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -424,13 +424,30 @@ 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->trailing_bits) {
+		struct spi_transfer t = {
+			.len = 1,
+			.tx_buf = empty_zero_page,
+		};
+
+		if (spi->trailing_bits < 4)
+			t.bits_per_word = 4;
+		else if (spi->trailing_bits > 8)
+			t.bits_per_word = 16;
+		else
+			t.bits_per_word = spi->trailing_bits;
+
+		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