[PATCH] spi: imx: only do necessary changes to ECSPIx_CONFIGREG

[PATCH] spi: imx: only do necessary changes to ECSPIx_CONFIGREG

[Dirk Behme]

From: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>

If the SPI chip select (CS) for a dedicated channel is done manually by
the used higher device driver, the CS may be active while writing to
ECSPIx_CONFIGREG. To prevent unwanted clock edges when selecting
the clock mode,  only do the necessary changes to the i.MX SPI
configuration register and leave not selected channels untouched.

To prevent unwanted clock edges on first use, an empty dummy
transmission shall be done by the initialization procedure of the device
driver of this channel. This will set the clock mode to the correct state.

Signed-off-by: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Dirk Behme <dirk.behme-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
---

This is regarding the discussion in

http://www.spinics.net/lists/arm-kernel/msg489107.html

and the revert

https://git.kernel.org/cgit/linux/kernel/git/broonie/spi.git/commit/drivers/spi/spi-imx.c?h=for-linus&id=c34de7168cd201ab757b11bfc7899953948d7753

This version is mainly the same like the reverted one, but making sure
that the cfg variable isn't just 0.

This patch is against

https://git.kernel.org/cgit/linux/kernel/git/broonie/spi.git/log/?h=for-linus

commit d00de215041f706

 drivers/spi/spi-imx.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index e7a19be..b79d70d 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -333,8 +333,9 @@ static void __maybe_unused mx51_ecspi_trigger(struct spi_imx_data *spi_imx)
 static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
 		struct spi_imx_config *config)
 {
-	u32 ctrl = MX51_ECSPI_CTRL_ENABLE, cfg = 0;
+	u32 ctrl = MX51_ECSPI_CTRL_ENABLE;
 	u32 clk = config->speed_hz, delay, reg;
+	u32 cfg = readl(spi_imx->base + MX51_ECSPI_CONFIG);
 
 	/*
 	 * The hardware seems to have a race condition when changing modes. The
@@ -358,13 +359,20 @@ static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
 
 	if (config->mode & SPI_CPHA)
 		cfg |= MX51_ECSPI_CONFIG_SCLKPHA(config->cs);
+	else
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKPHA(config->cs);
 
 	if (config->mode & SPI_CPOL) {
 		cfg |= MX51_ECSPI_CONFIG_SCLKPOL(config->cs);
 		cfg |= MX51_ECSPI_CONFIG_SCLKCTL(config->cs);
+	} else {
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKPOL(config->cs);
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKCTL(config->cs);
 	}
 	if (config->mode & SPI_CS_HIGH)
 		cfg |= MX51_ECSPI_CONFIG_SSBPOL(config->cs);
+	else
+		cfg &= ~MX51_ECSPI_CONFIG_SSBPOL(config->cs);
 
 	if (spi_imx->usedma)
 		ctrl |= MX51_ECSPI_CTRL_SMC;
-- 
2.5.0

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Re: [PATCH] spi: imx: only do necessary changes to ECSPIx_CONFIGREG

[Sascha Hauer]

On Tue, Mar 15, 2016 at 02:24:36PM +0100, Dirk Behme wrote:
> From: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
> 
> If the SPI chip select (CS) for a dedicated channel is done manually by
> the used higher device driver, the CS may be active while writing to
> ECSPIx_CONFIGREG. To prevent unwanted clock edges when selecting
> the clock mode,  only do the necessary changes to the i.MX SPI
> configuration register and leave not selected channels untouched.
> 
> To prevent unwanted clock edges on first use, an empty dummy
> transmission shall be done by the initialization procedure of the device
> driver of this channel. This will set the clock mode to the correct state.

The patch does the right thing, so:

Acked-by: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>

Only the above sentence is not clear to me. By device driver you mean
the SPI slave driver (flash, PMIC), right? Isn't this what
bitbang->setup_transfer(spi, NULL), called from spi_bitbang_setup() already
does? spi_bitbang_setup should be called while adding a new SPI slave
device and the setup_transfer with an empty message should setup the
config register correctly without involing the slave device driver.

Sascha


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Applied "spi: imx: only do necessary changes to ECSPIx_CONFIGREG" to the spi tree

[Mark Brown]

The patch

   spi: imx: only do necessary changes to ECSPIx_CONFIGREG

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

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

>From 793c7f9212fdb7bea5e017427e750afa11217c29 Mon Sep 17 00:00:00 2001
From: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
Date: Tue, 15 Mar 2016 14:24:36 +0100
Subject: [PATCH] spi: imx: only do necessary changes to ECSPIx_CONFIGREG

If the SPI chip select (CS) for a dedicated channel is done manually by
the used higher device driver, the CS may be active while writing to
ECSPIx_CONFIGREG. To prevent unwanted clock edges when selecting
the clock mode,  only do the necessary changes to the i.MX SPI
configuration register and leave not selected channels untouched.

To prevent unwanted clock edges on first use, an empty dummy
transmission shall be done by the initialization procedure of the device
driver of this channel. This will set the clock mode to the correct state.

Signed-off-by: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Dirk Behme <dirk.behme-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
Acked-by: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
Signed-off-by: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 drivers/spi/spi-imx.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index e7a19be87c38..b79d70d6dabf 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -333,8 +333,9 @@ static void __maybe_unused mx51_ecspi_trigger(struct spi_imx_data *spi_imx)
 static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
 		struct spi_imx_config *config)
 {
-	u32 ctrl = MX51_ECSPI_CTRL_ENABLE, cfg = 0;
+	u32 ctrl = MX51_ECSPI_CTRL_ENABLE;
 	u32 clk = config->speed_hz, delay, reg;
+	u32 cfg = readl(spi_imx->base + MX51_ECSPI_CONFIG);
 
 	/*
 	 * The hardware seems to have a race condition when changing modes. The
@@ -358,13 +359,20 @@ static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
 
 	if (config->mode & SPI_CPHA)
 		cfg |= MX51_ECSPI_CONFIG_SCLKPHA(config->cs);
+	else
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKPHA(config->cs);
 
 	if (config->mode & SPI_CPOL) {
 		cfg |= MX51_ECSPI_CONFIG_SCLKPOL(config->cs);
 		cfg |= MX51_ECSPI_CONFIG_SCLKCTL(config->cs);
+	} else {
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKPOL(config->cs);
+		cfg &= ~MX51_ECSPI_CONFIG_SCLKCTL(config->cs);
 	}
 	if (config->mode & SPI_CS_HIGH)
 		cfg |= MX51_ECSPI_CONFIG_SSBPOL(config->cs);
+	else
+		cfg &= ~MX51_ECSPI_CONFIG_SSBPOL(config->cs);
 
 	if (spi_imx->usedma)
 		ctrl |= MX51_ECSPI_CTRL_SMC;
-- 
2.7.0

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Re: [PATCH] spi: imx: only do necessary changes to ECSPIx_CONFIGREG

[Knut Wohlrab]

Am 03/17/2016 um 08:59 AM schrieb Sascha Hauer:
> On Tue, Mar 15, 2016 at 02:24:36PM +0100, Dirk Behme wrote:
>> > From: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/w@public.gmane.org>
>> > 
>> > If the SPI chip select (CS) for a dedicated channel is done manually by
>> > the used higher device driver, the CS may be active while writing to
>> > ECSPIx_CONFIGREG. To prevent unwanted clock edges when selecting
>> > the clock mode,  only do the necessary changes to the i.MX SPI
>> > configuration register and leave not selected channels untouched.
>> > 
>> > To prevent unwanted clock edges on first use, an empty dummy
>> > transmission shall be done by the initialization procedure of the device
>> > driver of this channel. This will set the clock mode to the correct state.
> The patch does the right thing, so:
> 
> Acked-by: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
> 
> Only the above sentence is not clear to me. By device driver you mean
> the SPI slave driver (flash, PMIC), right? Isn't this what
> bitbang->setup_transfer(spi, NULL), called from spi_bitbang_setup() already
> does? spi_bitbang_setup should be called while adding a new SPI slave
> device and the setup_transfer with an empty message should setup the
> config register correctly without involing the slave device driver.
> 
> Sascha
> 
"Higher device driver" is a "historical" protocol stack to unify our
data transfer via several physical interfaces, here SPI. This driver
requires own control to the CS signal to start data transfer only if CS
is acknowledged by the external SPI slave device via GPIO/IRQ. Therefore
we can not rely on iMX6 SPI controller IP or kernel driver CS/RDY
functionality. The CS signal is active before the SPI driver is involved
and if the SPI driver changes the clock polarity, the unwanted clock
edge is destroying the data transfer.

Thanks and regards

Knut
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