linux-kernel - [PATCH AUTOSEL 5.10 5/6] spi: spi-sun4i: fix early activation

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Message-Id: <20250519212320.1986749-5-sashal@kernel.org>
Date: Mon, 19 May 2025 17:23:19 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Alessandro Grassi <alessandro.grassi@...lbox.org>,
	Mark Brown <broonie@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	mripard@...nel.org,
	wens@...e.org,
	linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 5/6] spi: spi-sun4i: fix early activation

From: Alessandro Grassi <alessandro.grassi@...lbox.org>

[ Upstream commit fb98bd0a13de2c9d96cb5c00c81b5ca118ac9d71 ]

The SPI interface is activated before the CPOL setting is applied. In
that moment, the clock idles high and CS goes low. After a short delay,
CPOL and other settings are applied, which may cause the clock to change
state and idle low. This transition is not part of a clock cycle, and it
can confuse the receiving device.

To prevent this unexpected transition, activate the interface while CPOL
and the other settings are being applied.

Signed-off-by: Alessandro Grassi <alessandro.grassi@...lbox.org>
Link: https://patch.msgid.link/20250502095520.13825-1-alessandro.grassi@mailbox.org
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/spi/spi-sun4i.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 1fdfc6e6691d2..a8fba310d7004 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -263,6 +263,9 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	else
 		reg |= SUN4I_CTL_DHB;
 
+	/* Now that the settings are correct, enable the interface */
+	reg |= SUN4I_CTL_ENABLE;
+
 	sun4i_spi_write(sspi, SUN4I_CTL_REG, reg);
 
 	/* Ensure that we have a parent clock fast enough */
@@ -403,7 +406,7 @@ static int sun4i_spi_runtime_resume(struct device *dev)
 	}
 
 	sun4i_spi_write(sspi, SUN4I_CTL_REG,
-			SUN4I_CTL_ENABLE | SUN4I_CTL_MASTER | SUN4I_CTL_TP);
+			SUN4I_CTL_MASTER | SUN4I_CTL_TP);
 
 	return 0;
 
-- 
2.39.5