From: Matthew Fortune <matthew.fortune@mips.com>

Added very very basic nanoMIPS boot code but this is hacked in
unconditionally currently.

Signed-off-by: Yongbok Kim <yongbok.kim@mips.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Stefan Markovic <smarkovic@wavecomp.com>
---
 hw/mips/mips_malta.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 69 insertions(+), 6 deletions(-)

diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
index 3467451..4bc9036 100644
--- a/hw/mips/mips_malta.c
+++ b/hw/mips/mips_malta.c
@@ -620,6 +620,58 @@ static void network_init(PCIBus *pci_bus)
      a2 - 32-bit address of the environment variables table
      a3 - RAM size in bytes
 */
+static void write_bootloader_nanomips(uint8_t *base, int64_t run_addr,
+                                      int64_t kernel_entry)
+{
+    uint16_t *p;
+
+    /* Small bootloader */
+    p = (uint16_t *)base;
+
+#define NM_HI1(VAL) (((VAL) >> 16) & 0x1f)
+#define NM_HI2(VAL) \
+            (((VAL) & 0xf000) | (((VAL) >> 19) & 0xffc) | (((VAL) >> 31) & 0x1))
+#define NM_LO(VAL)  ((VAL) & 0xfff)
+
+    stw_p(p++, 0x2800); stw_p(p++, 0x001c); /* bc to_here */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+    stw_p(p++, 0x8000); stw_p(p++, 0xc000); /* nop */
+
+    /* to_here: */
+    stw_p(p++, 0x0080); stw_p(p++, 0x0002); /* li a0,2 */
+    stw_p(p++, 0xe3a0 | NM_HI1(ENVP_ADDR - 64));
+    stw_p(p++, NM_HI2(ENVP_ADDR - 64));
+                                /* lui sp,%hi(ENVP_ADDR - 64) */
+    stw_p(p++, 0x83bd); stw_p(p++, NM_LO(ENVP_ADDR - 64));
+                                /* ori sp,sp,%lo(ENVP_ADDR - 64) */
+    stw_p(p++, 0xe0a0 | NM_HI1(ENVP_ADDR));
+    stw_p(p++, NM_HI2(ENVP_ADDR));
+                                /* lui a1,%hi(ENVP_ADDR) */
+    stw_p(p++, 0x80a5); stw_p(p++, NM_LO(ENVP_ADDR));
+                                /* ori a1,a1,%lo(ENVP_ADDR) */
+    stw_p(p++, 0xe0c0 | NM_HI1(ENVP_ADDR + 8));
+    stw_p(p++, NM_HI2(ENVP_ADDR + 8));
+                                /* lui a2,%hi(ENVP_ADDR + 8) */
+    stw_p(p++, 0x80c6); stw_p(p++, NM_LO(ENVP_ADDR + 8));
+                                /* ori a2,a2,%lo(ENVP_ADDR + 8) */
+    stw_p(p++, 0xe0e0 | NM_HI1(loaderparams.ram_low_size));
+    stw_p(p++, NM_HI2(loaderparams.ram_low_size));
+                                /* lui a3,%hi(loaderparams.ram_low_size) */
+    stw_p(p++, 0x80e7); stw_p(p++, NM_LO(loaderparams.ram_low_size));
+                                /* ori a3,a3,%lo(loaderparams.ram_low_size) */
+    stw_p(p++, 0xe320 | NM_HI1(kernel_entry));
+    stw_p(p++, NM_HI2(kernel_entry));
+                                /* lui t9,%hi(kernel_entry) */
+    stw_p(p++, 0x8339); stw_p(p++, NM_LO(kernel_entry));
+                                /* ori t9,t9,%lo(kernel_entry) */
+    stw_p(p++, 0x4bf9); stw_p(p++, 0x0000);
+                                /* jalrc   t8 */
+}
 
 static void write_bootloader(uint8_t *base, int64_t run_addr,
                              int64_t kernel_entry)
@@ -813,10 +865,16 @@ static int64_t load_kernel (void)
                            NULL, (uint64_t *)&kernel_entry, NULL,
                            (uint64_t *)&kernel_high, big_endian, EM_MIPS, 1, 0);
     if (kernel_size < 0) {
-        error_report("could not load kernel '%s': %s",
-                     loaderparams.kernel_filename,
-                     load_elf_strerror(kernel_size));
-        exit(1);
+        kernel_size = load_elf(loaderparams.kernel_filename,
+                    cpu_mips_kseg0_to_phys, NULL,
+                    (uint64_t *)&kernel_entry, NULL,
+                    (uint64_t *)&kernel_high, big_endian, EM_NANOMIPS, 1, 0);
+        if (kernel_size < 0) {
+            error_report("could not load kernel '%s': %s",
+                         loaderparams.kernel_filename,
+                         load_elf_strerror(kernel_size));
+            exit(1);
+        }
     }
 
     /* Check where the kernel has been linked */
@@ -1096,8 +1154,13 @@ void mips_malta_init(MachineState *machine)
         loaderparams.initrd_filename = initrd_filename;
         kernel_entry = load_kernel();
 
-        write_bootloader(memory_region_get_ram_ptr(bios),
-                         bootloader_run_addr, kernel_entry);
+        if (!cpu_supports_isa(machine->cpu_type, ISA_NANOMIPS32)) {
+            write_bootloader(memory_region_get_ram_ptr(bios),
+                             bootloader_run_addr, kernel_entry);
+        } else {
+            write_bootloader_nanomips(memory_region_get_ram_ptr(bios),
+                                      bootloader_run_addr, kernel_entry);
+        }
         if (kvm_enabled()) {
             /* Write the bootloader code @ the end of RAM, 1MB reserved */
             write_bootloader(memory_region_get_ram_ptr(ram_low_preio) +
-- 
2.7.4

> From: Aleksandar Markovic <aleksandar.markovic@rt-rk.com>
> Sent: Monday, August 6, 2018 7:00 PM
> Subject: [PATCH v7 56/80] mips_malta: Add basic nanoMIPS boot code for MIPS' Malta
> 
> From: Matthew Fortune <matthew.fortune@mips.com>
> 
> Added very very basic nanoMIPS boot code but this is hacked in
> unconditionally currently.
> 
> Signed-off-by: Yongbok Kim <yongbok.kim@mips.com>
> Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
> Signed-off-by: Stefan Markovic <smarkovic@wavecomp.com>
> ---
>  hw/mips/mips_malta.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 69 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> 
> @@ -813,10 +865,16 @@ static int64_t load_kernel (void)
>                             NULL, (uint64_t *)&kernel_entry, NULL,
>                             (uint64_t *)&kernel_high, big_endian, EM_MIPS, 1, 0);
>      if (kernel_size < 0) {
> -        error_report("could not load kernel '%s': %s",
> -                     loaderparams.kernel_filename,
> -                     load_elf_strerror(kernel_size));
> -        exit(1);
> +        kernel_size = load_elf(loaderparams.kernel_filename,
> +                    cpu_mips_kseg0_to_phys, NULL,
> +                    (uint64_t *)&kernel_entry, NULL,
> +                    (uint64_t *)&kernel_high, big_endian, EM_NANOMIPS, 1, 0);
> +        if (kernel_size < 0) {
> +            error_report("could not load kernel '%s': %s",
> +                         loaderparams.kernel_filename,
> +                         load_elf_strerror(kernel_size));
> +            exit(1);
> +        }
>      }
> 

Instead of invoking load_elf() twice, in load_elf32 (aka glue(load_elf, SZ)), there should be something like this:

        case EM_MIPS:
        case EM_NANOMIPS:
            if ((ehdr.e_machine != EM_MIPS) &&
                (ehdr.e_machine != EM_NANOMIPS)) {
                    ret = ELF_LOAD_WRONG_ARCH;
                    goto fail;
                }
            }
            break;

In any case, Malta board should work with both EM_MIPS and EM_NANOMIPS. Please make sure both cases are well understood and tested.