[SeaBIOS] [RFC 2/2] Add Linux boot code for the fw_cfg dma interface

[Marc Marí]

It's probably not good to override all the ROM options. Better ways can
be discussed.

Signed-off-by: Marc Marí <markmb at redhat.com>
---
 src/boot.c        | 14 +++++++++++-
 src/fw/paravirt.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/fw/paravirt.h |  1 +
 src/romlayout.S   | 20 ++++++++++++++++
 4 files changed, 102 insertions(+), 1 deletion(-)

diff --git a/src/boot.c b/src/boot.c
index e0f73a3..7d187c5 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -684,6 +684,14 @@ boot_rom(u32 vector)
     call_boot_entry(so, 0);
 }
 
+// Boot from a linuxboot ROM when QEMU cfg is in DMA mode
+static void
+boot_linux_cfg_dma(void)
+{
+    printf("Booting Linux from fw_cfg...\n");
+    qemu_cfg_dma_boot_linux();
+}
+
 // Unable to find bootable device - warn user and eventually retry.
 static void
 boot_fail(void)
@@ -732,7 +740,11 @@ do_boot(int seq_nr)
         boot_cbfs((void*)ie->vector);
         break;
     case IPL_TYPE_BEV:
-        boot_rom(ie->vector);
+        if (qemu_cfg_dma_enabled()) {
+            boot_linux_cfg_dma();
+        } else {
+            boot_rom(ie->vector);
+        }
         break;
     case IPL_TYPE_HALT:
         boot_fail();
diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
index b7ab169..ada8574 100644
--- a/src/fw/paravirt.c
+++ b/src/fw/paravirt.c
@@ -23,6 +23,8 @@
 #include "util.h" // pci_setup
 #include "x86.h" // cpuid
 #include "xen.h" // xen_biostable_setup
+#include "bregs.h" // struct bregs
+#include "stacks.h" // farcall16big
 
 // Amount of continuous ram under 4Gig
 u32 RamSize;
@@ -554,3 +556,69 @@ void qemu_cfg_init(void)
         dprintf(1, "Moving pm_base to 0x%x\n", acpi_pm_base);
     }
 }
+
+void qemu_cfg_dma_boot_linux(void)
+{
+    dprintf(1, "Loading kernel\n");
+    void *setup_addr;
+    u32 setup_size;
+    qemu_cfg_read_entry(&setup_addr, QEMU_CFG_SETUP_ADDR, 4);
+    qemu_cfg_read_entry(&setup_size, QEMU_CFG_SETUP_SIZE, 4);
+    qemu_cfg_read_entry(setup_addr, QEMU_CFG_SETUP_DATA, setup_size);
+
+    if (readl(setup_addr + 0x202) != 0x53726448) {
+        dprintf(1, "Not valid kernel\n");
+        return;
+    }
+
+    u16 protocol = readw(setup_addr + 0x206);
+    if (protocol < 0x203) {
+        dprintf(1, "Old kernel (v %x) not supported\n", protocol);
+        return;
+    }
+
+    void *kernel_addr;
+    u32 kernel_size;
+
+    qemu_cfg_read_entry(&kernel_addr, QEMU_CFG_KERNEL_ADDR, 4);
+    qemu_cfg_read_entry(&kernel_size, QEMU_CFG_KERNEL_SIZE, 4);
+    qemu_cfg_read_entry(kernel_addr, QEMU_CFG_KERNEL_DATA, kernel_size);
+
+    void *cmdline_addr;
+    u32 cmdline_size;
+    qemu_cfg_read_entry(&cmdline_addr, QEMU_CFG_CMDLINE_ADDR, 4);
+    qemu_cfg_read_entry(&cmdline_size, QEMU_CFG_CMDLINE_SIZE, 4);
+    if (cmdline_size) {
+        qemu_cfg_read_entry(cmdline_addr, QEMU_CFG_CMDLINE_DATA, cmdline_size);
+    }
+
+    void *initrd_addr;
+    u32 initrd_size;
+    qemu_cfg_read_entry(&initrd_addr, QEMU_CFG_INITRD_ADDR, 4);
+    qemu_cfg_read_entry(&initrd_size, QEMU_CFG_INITRD_SIZE, 4);
+    if (initrd_size) {
+        qemu_cfg_read_entry(initrd_addr, QEMU_CFG_INITRD_DATA, initrd_size);
+    }
+
+    // Last configurations
+    writel(setup_addr + 0x228, cmdline_addr);
+    writeb(setup_addr + 0x210, 0xB0);
+    writeb(setup_addr + 0x211, readb(setup_addr + 0x211) | 0x80);
+    writew(setup_addr + 0x224, cmdline_addr - setup_addr - 0x200);
+    writel(setup_addr + 0x218, initrd_addr);
+    writel(setup_addr + 0x21c, initrd_size);
+
+    dprintf(1, "Jumping to kernel %d@%x %d@%x %d@%x %d@%x\n"
+            , setup_size, (u32)setup_addr, cmdline_size, (u32)cmdline_addr
+            , kernel_size, (u32)kernel_addr, initrd_size, (u32)initrd_addr);
+    struct bregs br;
+    memset(&br, 0, sizeof(br));
+    extern void kernel_stub(void);
+    br.ebx = (u32)setup_addr >> 4;
+    br.edx = (u32)cmdline_addr - (u32)setup_addr - 16;
+    br.code = SEGOFF(SEG_BIOS, (u32)kernel_stub - BUILD_BIOS_ADDR);
+
+    outb(0xa, 0xf4);
+
+    farcall16big(&br);
+}
diff --git a/src/fw/paravirt.h b/src/fw/paravirt.h
index a5fe913..c6a97c4 100644
--- a/src/fw/paravirt.h
+++ b/src/fw/paravirt.h
@@ -82,5 +82,6 @@ int qemu_cfg_dma_enabled(void);
 void qemu_preinit(void);
 void qemu_platform_setup(void);
 void qemu_cfg_init(void);
+void qemu_cfg_dma_boot_linux();
 
 #endif
diff --git a/src/romlayout.S b/src/romlayout.S
index 7938e22..1c641c2 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -196,6 +196,26 @@ __farcall16:
         IRQ_TRAMPOLINE 1c
         IRQ_TRAMPOLINE 4a
 
+        DECLFUNC kernel_stub
+kernel_stub:
+        movw %bx, %ds
+        movw %bx, %es
+        movw %bx, %fs
+        movw %bx, %gs
+        movw %bx, %ss
+        movl %edx, %esp
+        addw $0x20, %bx
+        pushw %bx    // push CS
+        pushw $0     // push IP
+        xorl %eax, %eax
+        xorl %ebx, %ebx
+        xorl %ecx, %ecx
+        xorl %edx, %edx
+        xorl %edi, %edi
+        xorl %esi, %esi
+        xorl %ebp, %ebp
+        lretw
+
 
 /****************************************************************
  * Misc. entry points.
-- 
2.4.3