arm64: zynqmp: Support semihosting boot method

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@linux.dev>
Link: https://lore.kernel.org/r/20240222200512.2679830-1-sean.anderson@linux.dev
Signed-off-by: Michal Simek <michal.simek@amd.com>

diff --git a/arch/arm/mach-zynqmp/spl.c b/arch/arm/mach-zynqmp/spl.c
index a0f35f36faaced6a28648bc12a5cdf87f5e4d885..5af735aa5cef0224d4fadbe1d9c63e206029cef4 100644 (file)
--- 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 */