linux-kernel - [PATCH v2] spi: sun4i: Prevent chip-select from being activated twice before a transfer

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Date:	Tue,  5 Jan 2016 21:46:20 +0100
From:	Marcus Weseloh <mweseloh42@...il.com>
To:	linux-sunxi@...glegroups.com
Cc:	Marcus Weseloh <mweseloh42@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] spi: sun4i: Prevent chip-select from being activated twice before a transfer

The SPI core calls set_cs before a transfer, but the SUN4I_CTL_CS_MANUAL
flag is only set in transfer_one. This leads to the following pattern on
the chip-select line (with runtime power-management on every transfer,
without it only on the first one):

activate, deactivate, activate, transfer, deactivate

Moving the configuration of the SUN4I_CTL_CS_MANUAL flag from transfer_one
to set_cs removes the double activation.

Signed-off-by: Marcus Weseloh <mweseloh42@...il.com>
Acked-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
---

Changes from v1:
- Added Maximes Acked-by

---

 drivers/spi/spi-sun4i.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index fbb0a4d..a6d936c 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -140,6 +140,9 @@ static void sun4i_spi_set_cs(struct spi_device *spi, bool enable)
 	reg &= ~SUN4I_CTL_CS_MASK;
 	reg |= SUN4I_CTL_CS(spi->chip_select);
 
+	/* We want to control the chip select manually */
+	reg |= SUN4I_CTL_CS_MANUAL;
+
 	if (enable)
 		reg |= SUN4I_CTL_CS_LEVEL;
 	else
@@ -222,9 +225,6 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	else
 		reg |= SUN4I_CTL_DHB;
 
-	/* We want to control the chip select manually */
-	reg |= SUN4I_CTL_CS_MANUAL;
-
 	sun4i_spi_write(sspi, SUN4I_CTL_REG, reg);
 
 	/* Ensure that we have a parent clock fast enough */
-- 
1.9.1

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