spi: imx: only do necessary changes to ECSPIx_CONFIGREG

From: Knut Wohlrab <[email protected]>

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.

---

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(-)

index e7a19be..b79d70d 100644
@@ -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

The patch does the right thing, so:

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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Am 03/17/2016 um 08:59 AM schrieb Sascha Hauer:

"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

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: Knut Wohlrab <knut.wohlrab-V5te9oGctAVWk0Htik3J/[email protected]>
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.

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

index e7a19be87c38..b79d70d6dabf 100644
@@ -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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