[PATCH] spi: spi-sun4i: fix early activation

[PATCH] spi: spi-sun4i: fix early activation

[Alessandro Grassi]

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@mailbox.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 f89826d7dc49..aa92fd5a35a9 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -264,6 +264,9 @@ static int sun4i_spi_transfer_one(struct spi_controller *host,
 	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 */
@@ -404,7 +407,7 @@ 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;
 
-- 
2.47.2

Re: [PATCH] spi: spi-sun4i: fix early activation

[Mark Brown]

On Fri, 02 May 2025 11:55:20 +0200, Alessandro Grassi wrote:
> 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.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: spi-sun4i: fix early activation
      commit: fb98bd0a13de2c9d96cb5c00c81b5ca118ac9d71

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

[PATCH] spi: spi-sun4i: fix early activation

[Alessandro Grassi]

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@mailbox.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 fcbe864c9b7d..4b070377e3d1 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -264,6 +264,9 @@ static int sun4i_spi_transfer_one(struct spi_controller *host,
 	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 */
@@ -404,7 +407,7 @@ 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;
 
-- 
2.45.2