spi: Add option to keep the MOSI line low, when it is idle.

[PATCH] spi: Add option to keep the MOSI line low, when it is idle.

Posted by Boerge Struempfel 2 years, 9 months ago

By default, the imx spi controller uses a high mosi line, whenever it is
idle. This may not be desired in all use cases. For example neopixel
leds can get confused and flicker due to misinterpreting the idle state.
Therefore, we introduce a new spi-mode bit, with which the idle behaviour
can be overwritten on a per device basis.

Signed-off-by: Boerge Struempfel <bstruempfel@ultratronik.de>
---
 drivers/spi/spi-imx.c        | 9 ++++++++-
 drivers/spi/spi.c            | 2 ++
 include/uapi/linux/spi/spi.h | 3 ++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index 34e5f81ec431e..6acab2b4ffaa5 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -281,6 +281,7 @@ static bool spi_imx_can_dma(struct spi_controller *controller, struct spi_device
 #define MX51_ECSPI_CONFIG_SCLKPOL(cs)	(1 << ((cs & 3) +  4))
 #define MX51_ECSPI_CONFIG_SBBCTRL(cs)	(1 << ((cs & 3) +  8))
 #define MX51_ECSPI_CONFIG_SSBPOL(cs)	(1 << ((cs & 3) + 12))
+#define MX51_ECSPI_CONFIG_DATACTL(cs)	(1 << ((cs & 3) + 16))
 #define MX51_ECSPI_CONFIG_SCLKCTL(cs)	(1 << ((cs & 3) + 20))
 
 #define MX51_ECSPI_INT		0x10
@@ -573,6 +574,11 @@ static int mx51_ecspi_prepare_message(struct spi_imx_data *spi_imx,
 		cfg &= ~MX51_ECSPI_CONFIG_SCLKCTL(spi_get_chipselect(spi, 0));
 	}
 
+	if (spi->mode & SPI_MOSI_IDLE_LOW)
+		cfg |= MX51_ECSPI_CONFIG_DATACTL(spi->chip_select);
+	else
+		cfg &= ~MX51_ECSPI_CONFIG_DATACTL(spi->chip_select);
+
 	if (spi->mode & SPI_CS_HIGH)
 		cfg |= MX51_ECSPI_CONFIG_SSBPOL(spi_get_chipselect(spi, 0));
 	else
@@ -1743,7 +1749,8 @@ static int spi_imx_probe(struct platform_device *pdev)
 	spi_imx->controller->prepare_message = spi_imx_prepare_message;
 	spi_imx->controller->unprepare_message = spi_imx_unprepare_message;
 	spi_imx->controller->slave_abort = spi_imx_slave_abort;
-	spi_imx->controller->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_NO_CS;
+	spi_imx->controller->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_NO_CS |
+					 SPI_MOSI_IDLE_LOW;
 
 	if (is_imx35_cspi(spi_imx) || is_imx51_ecspi(spi_imx) ||
 	    is_imx53_ecspi(spi_imx))
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9291b2a0e8871..3ad538b317a84 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2260,6 +2260,8 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 		spi->mode |= SPI_LSB_FIRST;
 	if (of_property_read_bool(nc, "spi-cs-high"))
 		spi->mode |= SPI_CS_HIGH;
+	if (of_property_read_bool(nc, "spi-mosi-idle-low"))
+		spi->mode |= SPI_MOSI_IDLE_LOW;
 
 	/* Device DUAL/QUAD mode */
 	if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index 9d5f580597039..ca56e477d1619 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -28,6 +28,7 @@
 #define	SPI_RX_OCTAL		_BITUL(14)	/* receive with 8 wires */
 #define	SPI_3WIRE_HIZ		_BITUL(15)	/* high impedance turnaround */
 #define	SPI_RX_CPHA_FLIP	_BITUL(16)	/* flip CPHA on Rx only xfer */
+#define SPI_MOSI_IDLE_LOW	_BITUL(17)	/* leave mosi line low when idle */
 
 /*
  * All the bits defined above should be covered by SPI_MODE_USER_MASK.
@@ -37,6 +38,6 @@
  * These bits must not overlap. A static assert check should make sure of that.
  * If adding extra bits, make sure to increase the bit index below as well.
  */
-#define SPI_MODE_USER_MASK	(_BITUL(17) - 1)
+#define SPI_MODE_USER_MASK	(_BITUL(18) - 1)
 
 #endif /* _UAPI_SPI_H */
-- 
2.25.1

[PATCH v2 0/4] spi: Add option to keep the MOSI line low, when it is idle

Posted by Boerge Struempfel 2 years, 9 months ago

Some spi controller like the imx spi controller switch the mosi line to
high, whenever they are idle. This may not be desired in all use cases.
For example neopixel leds can get confused and flicker due to
misinterpreting the idle state. Therefore, we introduce a new spi-mode
bit, with which the idle behaviour can be overwritten on a per device
basis.

Changes from V1:
  - Added patch, introducing the new devicetree binding flag
  - Split the generic spi part of the patch from the imx-spi specific
    part
  - Replaced SPI_CPOL and SPI_CPHA by the combined SPI_MODE_X_MASK bit
    in the imx-spi.c modebits.
  - Added the SPI_MOSI_IDLE_LOW bit to spidev

Boerge Struempfel (4):
  spi: dt-bindings: Introduce spi-mosi-idle-low flag
  spi: add SPI_MOSI_IDLE_LOW mode bit
  spi: spi-imx: add support for SPI_MOSI_IDLE_LOW mode bit
  spi: spidev: add SPI_MOSI_IDLE_LOW mode bit

 .../devicetree/bindings/spi/spi-peripheral-props.yaml    | 6 ++++++
 drivers/spi/spi-imx.c                                    | 9 ++++++++-
 drivers/spi/spi.c                                        | 2 ++
 drivers/spi/spidev.c                                     | 2 +-
 include/uapi/linux/spi/spi.h                             | 3 ++-
 5 files changed, 19 insertions(+), 3 deletions(-)

-- 
2.25.1

Re: [PATCH v2 0/4] spi: Add option to keep the MOSI line low, when it is idle

Posted by Mark Brown 2 years, 9 months ago

On Fri, May 12, 2023 at 01:13:13AM +0200, Boerge Struempfel wrote:
> Some spi controller like the imx spi controller switch the mosi line to
> high, whenever they are idle. This may not be desired in all use cases.
> For example neopixel leds can get confused and flicker due to
> misinterpreting the idle state. Therefore, we introduce a new spi-mode
> bit, with which the idle behaviour can be overwritten on a per device
> basis.

Please don't send new patches in reply to old patches or serieses, this
makes it harder for both people and tools to understand what is going
on - it can bury things in mailboxes and make it difficult to keep track
of what current patches are, both for the new patches and the old ones.

[PATCH v2 1/4] spi: dt-bindings: Introduce spi-mosi-idle-low flag

Posted by Boerge Struempfel 2 years, 9 months ago

Some spi controller switch the mosi line to high, whenever they are
idle. This may not be desired in all use cases. For example neopixel
leds can get confused and flicker due to misinterpreting the idle state.
Therefore, we introduce a new spi-mode bit, with which the idle behaviour
can be overwritten on a per device basis.

Signed-off-by: Boerge Struempfel <bstruempfel@ultratronik.de>
---
 .../devicetree/bindings/spi/spi-peripheral-props.yaml       | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
index 782a014b63a76..46d5acc1fc232 100644
--- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
+++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
@@ -34,6 +34,12 @@ properties:
     description:
       The device requires the chip select active high.
 
+  spi-mosi-idle-low:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description:
+      The device requires the mosi line to be low when idle and the
+      chip select is asserted.
+
   spi-lsb-first:
     $ref: /schemas/types.yaml#/definitions/flag
     description:
-- 
2.25.1