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

Am Mo., 15. Mai 2023 um 08:37 Uhr schrieb Mahapatra, Amit Kumar
[off-list ref]:

Hello,

quoted

-----Original Message-----
From: Boerge Struempfel <boerge.struempfel@gmail.com>
Sent: Thursday, May 11, 2023 7:27 PM
Cc: boerge.struempfel@gmail.com; bstruempfel@ultratronik.de; Mark
Brown [off-list ref]; Shawn Guo [off-list ref]; Sascha
Hauer [off-list ref]; Pengutronix Kernel Team
[off-list ref]; Fabio Estevam [off-list ref]; NXP
Linux Team [off-list ref]; linux-spi@vger.kernel.org; linux-arm-
kernel@lists.infradead.org; linux-kernel@vger.kernel.org
Subject: [PATCH] spi: Add option to keep the MOSI line low, when it is idle.

CAUTION: This message has originated from an External Source. Please use
proper judgment and caution when opening attachments, clicking links, or
responding to this email.


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 <redacted>
---
 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);

Kindly replace all occurrence of spi->chip_select with spi_get_chipselect(spi, 0)
https://github.com/torvalds/linux/commit/9e264f3f85a56cc109cc2d6010a48aa89d5c1ff1

Thank you very much for noticing this. I have changed it for the next
version of the patch.

quoted

+       else
+               cfg &= ~MX51_ECSPI_CONFIG_DATACTL(spi->chip_select);

quoted

+
        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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel