[PATCH] arm64: zynqmp: Support semhosting boot method

[Michal Simek]

On 2/15/24 18:19, Sean Anderson wrote:
> Currently, when we boot from JTAG we try to boot U-Boot from RAM.
> However, this is a bit tricky to time, since the debugger has to wait
> for SPL to initialize RAM before it can load U-Boot. This can result in
> long waits, since occasionally initializing RAM (and other things in
> psu_init) takes a long time to complete and the debugger must wait for
> this worst case.
> 
> Support semihosting if it is enabled, as it lets U-Boot tell the
> debugger when we are ready for the image. This means we don't have to
> wait any more than necessary. We don't change the default config to
> ensure we don't break compatibility with existing debuggers that don't
> expect us to hit semihosting breakpoints.
> 
> Signed-off-by: Sean Anderson <sean.anderson at seco.com>
> ---
> 
>   arch/arm/mach-zynqmp/spl.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mach-zynqmp/spl.c b/arch/arm/mach-zynqmp/spl.c
> index a0f35f36faa..5af735aa5ce 100644
> --- a/arch/arm/mach-zynqmp/spl.c
> +++ b/arch/arm/mach-zynqmp/spl.c
> @@ -9,6 +9,7 @@
>   #include <image.h>
>   #include <init.h>
>   #include <log.h>
> +#include <semihosting.h>
>   #include <spl.h>
>   #include <linux/delay.h>
> 
> @@ -66,6 +67,11 @@ void spl_board_init(void)
>   }
>   #endif
> 
> +static u32 jtag_boot_device(void)
> +{
> +       return semihosting_enabled() ? BOOT_DEVICE_SMH : BOOT_DEVICE_RAM;
> +}
> +
>   void board_boot_order(u32 *spl_boot_list)
>   {
>          spl_boot_list[0] = spl_boot_device();
> @@ -75,7 +81,7 @@ void board_boot_order(u32 *spl_boot_list)
>          if (spl_boot_list[0] == BOOT_DEVICE_MMC2)
>                  spl_boot_list[1] = BOOT_DEVICE_MMC1;
> 
> -       spl_boot_list[2] = BOOT_DEVICE_RAM;
> +       spl_boot_list[2] = jtag_boot_device();
>   }
> 
>   u32 spl_boot_device(void)
> @@ -97,7 +103,7 @@ u32 spl_boot_device(void)
> 
>          switch (bootmode) {
>          case JTAG_MODE:
> -               return BOOT_DEVICE_RAM;
> +               return jtag_boot_device();
>   #ifdef CONFIG_SPL_MMC
>          case SD_MODE1:
>          case SD1_LSHFT_MODE: /* not working on silicon v1 */

Good timing. Can you please tell me how to test this? What's the setup?
Which debugger are you using?

Also curious if semihosting serial can be used in your setup.

Thanks,
Michal