HDP Linux driver




1 Article purpose[edit]

This article introduces the Hardware Debug Port which allows the observation of internal signals. By using multiplexers, up to 16 signals of each of 8-bit output can be observed. The article explains:

  • How to configure, use and debug the driver
  • The driver structure, and where the source code can be found.

2 Short description[edit]

  • 8 output signals
  • One of 16 internal signals with individual control
  • 8 software-programmable signals for pinout agnostic code debugging
  • Output disabling by security signal
Alternate text
HDP Block Diagram

3 Configuration[edit]

3.1 Kernel configuration[edit]

The HDP is enabled and ready to be used in all STM32MPU Embedded Software Distributions, via the Linux® kernel configuration CONFIG_STM32_HDP, set to disabled by default.

Symbol: STM32_HDP
Location:
  Device Drivers
  [*] SOC (System On Chip) specific Drivers
    [*] STMicroelectronics STM32MP157 Hardware Debug Port (HDP) pin control 

Please refer to the Menuconfig or how to configure kernel article for instructions on modifying the configuration, and recompiling the Linux kernel image in the Distribution Package context.

3.2 Device tree[edit]

Refer to the HDP device tree configuration article when configuring the HDP Linux kernel driver.

4 How to trace and debug[edit]

4.1 How to monitor[edit]

4.1.1 How to monitor with debugfs[edit]

sysfs entry can be used to browse HDP registers.

 Board $> /sys/kernel/debug/hdp# ls
  ctrl  gpoclr  gposet  gpoval  mux  val

See the HDP chapter in the reference manual [1] for further register details.

5 Source code location[edit]

The HDP Linux driver source code is composed of:

  • “<Linux kernel directory>/drivers/soc/st/stm32_hdp.c” to handle common resources: registers, clock.
Info.png Please note that the upstreaming of the HDP Linux driver source code is in progress

6 References[edit]

Hardware Debug Port

Debug File System (See https://en.wikipedia.org/wiki/Debugfs for more details)

System File System (See https://en.wikipedia.org/wiki/Sysfs for more details)

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