Hardware CS control in SPI

[y.kim]

By the help in this forum, I can put a small delay between packets in the SPI communication.

The test code sends 35 16-bit packets with 8-clock delay between them.

This is the patch I made:

---
 .../t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi    | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi b/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi
index 2b81267506b0..cc6c2305e688 100644
--- a/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi
+++ b/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi
@@ -416,6 +416,8 @@
 
 	spi@3210000{ /* SPI1 in 40 pin conn */
 		status = "okay";
+		num-cs = <1>;
+		cs-gpios = <&tegra_main_gpio TEGRA194_MAIN_GPIO(Z, 6) GPIO_ACTIVE_LOW>; /* from Jetson_Xavier_Nx_Pinmux_Configuration */
 		spi@0 { /* chip select 0 */
 			compatible = "spidev";
 			reg = <0x0>;
@@ -424,6 +426,7 @@
 				nvidia,enable-hw-based-cs;
 				nvidia,rx-clk-tap-delay = <0x10>;
 				nvidia,tx-clk-tap-delay = <0x0>;
+				nvidia,cs-inactive-cycles = <0x08>;
 			};
 		};
 		spi@1 { /* chip select 1 */

What I want to do is to put the CS high(inactive) during the delay between packets.

Here is the desired CS pattern in the red line:

I read SPI_CS_TIMING2 in tegra_spi_start_transfer_one function.
It reports 0x8 because it uses CS0 only. The CS doesn’t go high during the delay even I set it to 0x28. It doesn’t make any change if I set CS_ACTIVE_BETWEEN_PACKETS_0 to 0 or 1:

[DaneLLL]

Hi,
Do you use Jetpack 4 or Jetpack 5?

[y.kim]

Hi Dane,

I should have mentioned this. I am using Yocto dunfell. The kernel version is 4.9.201-rt134-l4t-r32.5. This is the last commit from linux-tegra:

commit bae75202eec6c39328a3626615f68b9f0de74ed9 (origin/oe4t-patches-l4t-r32.5, oe4t-patches-l4t-r32.5)
Author: Derrick T. Woolworth <dwoolworth@gmail.com>
Date:   Wed Mar 10 14:40:31 2021 -0600

    iscsi_tcp: fix compilation warnings with NVIDIA downstream kernel
    
    Commit 28ef6f8081ae6d2206185a627652427ce8e83462 changed the types of
    some fields in scatterlist.h, which require corresponding changes in iscsi_tcp.

And we have added some custom commits that are not related to spi-tegra driver, on top of that.
Please advise me if you are still lack of information about my environment.

[y.kim]

SPI_COMMAND_0 is 0xf3c0182f just before the return of tegra_spi_start_transfer_one function. It looks good for me.

[y.kim]

I found the answer. I shouldn’t use num-cs and cs-gpios:

 	spi@3210000{ /* SPI1 in 40 pin conn */
 		status = "okay";
+		num-cs = <1>;
+		cs-gpios = <&tegra_main_gpio TEGRA194_MAIN_GPIO(Z, 6) GPIO_ACTIVE_LOW>; /* from Jetson_Xavier_Nx_Pinmux_Configuration */
 		spi@0 { /* chip select 0 */
 			compatible = "spidev";
 			reg = <0x0>;