[SeaBIOS] Re: [PATCH v2 2/2] Add basic MXM 3.0 interrupt support

[Riku Viitanen]

VGAROMs on MXM graphics cards need certain int15h functions present
to function properly.

On HP EliteBook 8560w with coreboot and Quadro 2000M, this warning
is displayed for 30 seconds, making every boot extremely slow:

ERROR: Valid MXM Structure not found
    POST halted for 30 seconds, P-state limited to P10...

This patch implements the minimum functionality to get rid of it: the
functions 0 and 1, version 3.0 of the specification [1]. Older version
2.1 is not implemented.

Functions are enabled only if romfile "mxm-30-sis" exists. These functions
are specific to the MXM revision, but not the board or GPU. Some boards
might require more of the optional functions to be implemented, however.

- Function 0 returns information about supported functions and revision.

- Function 1 returns a pointer to a MXM configuration structure in low
memory. This is copied from romfile "mxm-30-sis". It can be extracted
from vendor BIOS, by using this same interrupt. I wrote a tool [2] to do
that from Linux.

TEST: HP EliteBook 8560w boots without error and delay, graphics work.

[1]: MXM Graphics Module Software Specification Version 3.0, Revision 1.1
[2]: https://codeberg.org/Riku_V/mxmdump/

Signed-off-by: Riku Viitanen 
---
 src/Kconfig      |  2 +-
 src/optionroms.c |  8 ++++++
 src/vgahooks.c   | 70 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/vgahooks.h   |  8 ++++++
 4 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 src/vgahooks.h

diff --git a/src/Kconfig b/src/Kconfig
index 3a8ffa15..8cadad2c 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -452,7 +452,7 @@ menu "BIOS interfaces"
         default y
         help
             Support int 155f BIOS callbacks specific to some Intel and
-            VIA on-board vga devices.
+            VIA on-board vga devices and MXM graphics cards.

config DISABLE_A20
         bool "Disable A20"
diff --git a/src/optionroms.c b/src/optionroms.c
index e906ab97..4e6a1ad1 100644
--- a/src/optionroms.c
+++ b/src/optionroms.c
@@ -22,6 +22,7 @@
 #include "string.h" // memset
 #include "util.h" // get_pnp_offset
 #include "tcgbios.h" // tpm_*
+#include "vgahooks.h" // MXM30SIS

static int EnforceChecksum, S3ResumeVga, RunPCIroms;

@@ -463,6 +464,13 @@ vgarom_setup(void)
     RunPCIroms = romfile_loadint("etc/pci-optionrom-exec", 2);
     ScreenAndDebug = romfile_loadint("etc/screen-and-debug", 1);

+    // Load MXM 3.0 System Information Structure, if it exists
+    void *mxm_sis = romfile_loadfile_low("mxm-30-sis", NULL);
+    if (mxm_sis)
+        MXM30SIS = (u32)mxm_sis;
+    else
+        MXM30SIS = 0;
+
     // Clear option rom memory
     memset((void*)BUILD_ROM_START, 0, rom_get_max() - BUILD_ROM_START);

diff --git a/src/vgahooks.c b/src/vgahooks.c
index 1f149532..25e91f20 100644
--- a/src/vgahooks.c
+++ b/src/vgahooks.c
@@ -18,8 +18,10 @@
 #define VH_VIA 1
 #define VH_INTEL 2
 #define VH_SMI 3
+#define VH_MXM 4

int VGAHookHandlerType VARFSEG;
+u32 MXM30SIS VARFSEG;

static void
 handle_155fXX(struct bregs *regs)
@@ -296,6 +298,71 @@ winent_mb6047_setup(struct pci_device *pci)
     SmiBootDisplay = 0x02;
 }

+/****************************************************************
+ * MXM VGA hooks
+ ****************************************************************/
+
+// Function 0: Return Specification Support Level
+static void
+mxm_V30_F00(struct bregs *regs)
+{
+    regs->ax = 0x005f; // Success
+    regs->bl = 0x30; // MXM 3.0
+    regs->cx = 0x0003; // Supported Functions
+    set_success(regs);
+}
+
+// Function 1: Return a Pointer to the MXM Structure
+static void
+mxm_V30_F01(struct bregs *regs)
+{
+    switch (regs->cx) {
+    case 0x0030:
+        regs->ax = 0x005f; // Success
+        regs->es = GET_GLOBAL(MXM30SIS)/16;
+        regs->di = GET_GLOBAL(MXM30SIS)%16;
+        set_success(regs);
+        break;
+    default:
+        handle_155fXX(regs);
+        break;
+    }
+}
+
+static void
+mxm_V30(struct bregs *regs)
+{
+    switch (regs->bx) {
+    case 0xff00: mxm_V30_F00(regs); break;
+    case 0xff01: mxm_V30_F01(regs); break;
+    default:   handle_155fXX(regs); break;
+    }
+}
+
+static void
+mxm_155f80(struct bregs *regs)
+{
+    // TODO: implement other versions, like 2.1
+    mxm_V30(regs);
+}
+
+static void
+mxm_155f(struct bregs *regs)
+{
+    switch (regs->al) {
+    case 0x80: mxm_155f80(regs); break;
+    default:   handle_155fXX(regs); break;
+    }
+}
+
+void
+mxm_setup(void)
+{
+    VGAHookHandlerType = VH_MXM;
+}
+
+
+
 /****************************************************************
  * Entry and setup
  ****************************************************************/
@@ -313,6 +380,7 @@ handle_155f(struct bregs *regs)
     switch (htype) {
     case VH_VIA:   via_155f(regs); break;
     case VH_INTEL: intel_155f(regs); break;
+    case VH_MXM:   mxm_155f(regs); break;
     default:       handle_155fXX(regs); break;
     }
 }
@@ -352,4 +420,6 @@ vgahook_setup(struct pci_device *pci)
         via_setup(pci);
     else if (pci->vendor == PCI_VENDOR_ID_INTEL)
         intel_setup(pci);
+    else if (GET_GLOBAL(MXM30SIS))
+        mxm_setup();
 }
diff --git a/src/vgahooks.h b/src/vgahooks.h
new file mode 100644
index 00000000..c9113714
--- /dev/null
+++ b/src/vgahooks.h
@@ -0,0 +1,8 @@
+#ifndef __VGAHOOKS_H
+#define __VGAHOOKS_H
+
+#include "types.h" // u32
+
+extern u32 MXM30SIS;
+
+#endif // vgahooks.h