SK-AM62A-LP: [SDK 10.00.00] SPI D0 and D1 pins assigned to MOSI and MISO

Hi Ramy,

Ramy Anous said:

The query here is how to identify whether D0 assigned to MOSI or MISO?

I was expecting D0 assigned to MOSI and D1 assigned to MISO.

By default, D0 is MISO, and D1 is MOSI. There is a device-tree property called ti,pindir-d0-out-d1-in that reverses the default order. Looking up the associated device tree node binding documentation always helps remembering what is what:

a0797059@jiji:~/git/linux (master)
$ git grep -A 5 ti,pindir-d0-out-d1-in\:
Documentation/devicetree/bindings/spi/omap-spi.yaml:  ti,pindir-d0-out-d1-in:
Documentation/devicetree/bindings/spi/omap-spi.yaml-    description:
Documentation/devicetree/bindings/spi/omap-spi.yaml-      Select the D0 pin as output and D1 as input. The default is D0
Documentation/devicetree/bindings/spi/omap-spi.yaml-      as input and D1 as output.
Documentation/devicetree/bindings/spi/omap-spi.yaml-    type: boolean
Documentation/devicetree/bindings/spi/omap-spi.yaml-

Ramy Anous said:

Another query, What If I want to use spidev to test SPI0 as a slave?

We don't officially support SPI slave operation with the Linux SDK/driver. While there's ways to make it work there are some constraints, and you would be better off using a different communication scheme (high-speed UART, for example -- but that really depends on your system).

Regards, Andreas

Hi Ramy,

Ramy Anous said:

Regarding the SPI slave, I get that it's not supported officially, But Do you have any guide/manual/steps on what changes need to be done to have SPI working as Slave?

In essence, you need to add DMA-related properties (dmas and dma-names) to the device tree node, and then also add spi-slave to the SPI peripheral device tree node, like this:

$ git show
commit 30253dd73e444c451cf352b2b005d32e03b080be (HEAD -> ti-linux-6.6.y-spi-slave-dev)
Author: Andreas Dannenberg <dannenberg@ti.com>
Date:   Wed Nov 13 15:15:04 2024 -0600

    arm64: dts: ti: k3-am62a: Configure SPI0 as Slave-Mode spidev Device

    Note that the SPI Slave in Linux doesn’t implement flow-control by default
    and custom flow control mechanism need to be implemented according to the
    application for deterministic performance.

    Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>

diff --git a/arch/arm64/boot/dts/ti/k3-am62a7-sk.dts b/arch/arm64/boot/dts/ti/k3-am62a7-sk.dts
index 3047586a6d9d..b582f08d1fe1 100644
--- a/arch/arm64/boot/dts/ti/k3-am62a7-sk.dts
+++ b/arch/arm64/boot/dts/ti/k3-am62a7-sk.dts
@@ -451,6 +451,15 @@ AM62AX_IOPAD(0x028, PIN_INPUT, 0) /* (J22) OSPI0_D7 */
                        AM62AX_IOPAD(0x008, PIN_INPUT, 0) /* (J24) OSPI0_DQS */
                >;
        };
+
+       main_spi0_pins_default: main-spi-pins-default {
+               pinctrl-single,pins = <
+                       AM62AX_IOPAD(0x01bc, PIN_INPUT, 0) /* (A17) SPI0_CLK */
+                       AM62AX_IOPAD(0x01b4, PIN_INPUT, 0) /* (D16) SPI0_CS0 */
+                       AM62AX_IOPAD(0x01c0, PIN_INPUT, 0) /* (B15) SPI0_D0 */
+                       AM62AX_IOPAD(0x01c4, PIN_INPUT, 0) /* (E15) SPI0_D1 */
+               >;
+       };
 };

 &mcu_pmx0 {
@@ -944,3 +953,25 @@ partition@7fc0000 {
                };
        };
 };
+
+&main_spi0 {
+               status = "okay";
+               #address-cells = <0>;
+               #size-cells = <0>;
+               pinctrl-names = "default";
+               pinctrl-0 = <&main_spi0_pins_default>;
+               ti,pindir-d0-out-d1-in = <1>;
+               spi-slave;
+               dmas = <&main_pktdma 0xc300 0>, <&main_pktdma 0x4300 0>;
+               dma-names = "tx0", "rx0";
+
+               slave {
+                               /*
+                                * Using spidev compatible is warned loudly,
+                                * thus use another equivalent compatible id
+                                * from spidev.
+                                */
+                               compatible = "rohm,dh2228fv";
+                               spi-max-frequency = <24000000>;
+               };
+};

Then when you boot, you can find the slave device here:

root@am62axx-evm:/opt/edgeai-gst-apps# ls -al /dev/spi*
crw------- 1 root root 153, 0 Jan  1 00:00 /dev/spidev1.0

root@am62axx-evm:/opt/edgeai-gst-apps# ls -al /sys/class/spi_slave/
total 0
drwxr-xr-x  2 root root 0 Jan  1 00:08 .
drwxr-xr-x 81 root root 0 Jan  1 00:08 ..
lrwxrwxrwx  1 root root 0 Jan  1 00:08 spi1 -> ../../devices/platform/bus@f0000/20100000.spi/spi_slave/spi1

And then you _should_ be able to try it like this using spidev_test. In my case it hangs because I don't have anything that's clocking in data...

root@am62axx-evm:/opt/edgeai-gst-apps# ./spidev_test -D /dev/spidev1.0 -v -p "12345678"
spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 kHz)

Here are some applicable E2E threads with additional information that might be helpful:

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1262607/am3351-linux-support-for-spi-as-a-slave-device/4780250

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1301459/tda4al-q1-regarding-mcu-spi-slave-mode-configuration-issues

Please let me know if you get it to work; it will be helpful for everybody if you can share your findings.

Thanks, Andreas

Hi Andreas,

I just wanted to update you that I've been able use SPI2 as a slave after updating the PSI-L thread ID.

Attaching the DTS changes below.

&main_spi2 {
	pinctrl-names = "default";
	pinctrl-0 = <&main_spi2_pins_default>;
    status = "okay";
	ti,pindir-d0-out-d1-in;
	spi-slave;
	dmas = <&main_pktdma 0xc308 0>, <&main_pktdma 0x4308 0>;
	dma-names = "tx0", "rx0";	

	slave {
                spi-max-frequency = <24000000>;
                compatible = "rohm,dh2228fv";
        };

};