[PATCH] multiboot: Use DMA instead port-based transfer

[Adam Lackorzynski]

Use DMA transfers in the multiboot loader to copy
data.

This significantly lowers QEMU's startup latency by
a factor of about 40, for example, going from 30sec
to 0.8sec when loading modules of 120MB in size.
This change has been used successfully for some time.

Signed-off-by: Marcus Hähnel <marcus.haehnel@kernkonzept.com>
Signed-off-by: Adam Lackorzynski <adam@l4re.org>
---
 pc-bios/multiboot.bin         | Bin 1024 -> 1536 bytes
 pc-bios/optionrom/multiboot.S |  10 ++---
 pc-bios/optionrom/optionrom.h |  77 ++++++++++++++++++++++++++++++++++
 3 files changed, 82 insertions(+), 5 deletions(-)

diff --git a/pc-bios/multiboot.bin b/pc-bios/multiboot.bin
index 
e772713c95749bee82c20002b50ec6d05b2d4987..94dc3fc9644ad2e1c87a3ac62a60cce659ada04f
 100644
GIT binary patch
literal 1536
zcmds1&ubG=5S~qT?GnMHKP*K`h!WyKk>(<ZA_&c~7}5R#%H}IVH4u|y53=;|NZ5lX
z@gRsdLGZZ7%WiV$qLfDP5b0%GFG*Uchf0G4*4a(gOZA{s1t09r_ukC=X6C(bckxB^
z9sO|3QaXP>FGWJ<31w0V@s$A79HaepfSLo_l~H>SdrOA+1nDF6ZVLMD9PF-abWu&V
zWk}5eM3U%@N(GUWshU(32FHlqF=gad30cdqAhx0RreGfDM9iLm?nL-e5qFj#=F^{H
z%D!tf-G^v}cmUI{E(q&GxX?QZ_SI(;?7@`$T?fP9>MiCu-Kcz7LUlg93t@lH8}q~d
zTHZC76F*HToUk+QvLE8#=<?q*XLn@7U7x^X4bNrL@NA9`me(v~H<9)9H5sp`{N~M6
zhu`)5wS}AOCrgtVzQF4PNE@2CdY-VlS^1FlP$x=|c9~bo7kO(2`bt8oq%)}IWUN}1
zQ;ZZ`YLvz^h~`vA55^!GS#RepFRTo9nt0grIbio<8pJe<5pijnRTxMke#R=myFg?n
zxF(}zv<=H}jgHu6Ihrc3u_#!JEXBCv>oAaE0QW^Ju!BH;?CT4cr5AU=(%TEz4>-aX
z9c!-dD^A!$-m#<RT{FiIQwnEPXa85~99HO`#-Hfi|IUt-w`oRRy*%e_%|wa(>k5bG
uF?zB=fqgWxPiZtKI!iA9P;TTF7U^DPxqSCdu~<$m7jJ8YQb_SX+SzZT$^;((

delta 357
zcmZqRY2aW9UBz^IvLUP3L@5E5X-u=3ChA$%CorWk9!^c`lw)An&B2h`DaXRlEjNJ)
z$Y5hg>z11YljdMZGd$3DU<Vh&E&<l}y98O^q#b;~flTn9Nb5YlgB!2>!5u;jX+Q%Q
z7(hn+`J5w**TBgMOvmffcCdr>q`glASqriihWSr)9#7i=bQ;h|?9vC*b_jx8#J~WN
w2U?l7Ljb=9E);1=RQnF^VA`-&`~O3R-HelOu^2FAFiqxR{XE%$wSw^v0Movl^Z)<=

diff --git a/pc-bios/optionrom/multiboot.S b/pc-bios/optionrom/multiboot.S
index b7efe4de34..5fe4da6486 100644
--- a/pc-bios/optionrom/multiboot.S
+++ b/pc-bios/optionrom/multiboot.S
@@ -68,10 +68,10 @@ run_multiboot:
        mov             %eax, %es
 
        /* Read the bootinfo struct into RAM */
-       read_fw_blob(FW_CFG_INITRD)
+       read_fw_blob_dma(FW_CFG_INITRD)
 
        /* FS = bootinfo_struct */
-       read_fw         FW_CFG_INITRD_ADDR
+       read_fw_dma_var32       FW_CFG_INITRD_ADDR
        shr             $4, %eax
        mov             %ax, %fs
 
@@ -188,14 +188,14 @@ prot_mode:
        movl            %eax, %gs
 
        /* Read the kernel and modules into RAM */
-       read_fw_blob(FW_CFG_KERNEL)
+       read_fw_blob_dma(FW_CFG_KERNEL)
 
        /* Jump off to the kernel */
-       read_fw         FW_CFG_KERNEL_ENTRY
+       read_fw_dma_var32 FW_CFG_KERNEL_ENTRY
        mov             %eax, %ecx
 
        /* EBX contains a pointer to the bootinfo struct */
-       read_fw         FW_CFG_INITRD_ADDR
+       read_fw_dma_var32       FW_CFG_INITRD_ADDR
        movl            %eax, %ebx
 
        /* EAX has to contain the magic */
diff --git a/pc-bios/optionrom/optionrom.h b/pc-bios/optionrom/optionrom.h
index a2b612f1a7..5a88c7c5a3 100644
--- a/pc-bios/optionrom/optionrom.h
+++ b/pc-bios/optionrom/optionrom.h
@@ -37,6 +37,17 @@
 #define BIOS_CFG_IOPORT_CFG    0x510
 #define BIOS_CFG_IOPORT_DATA   0x511
 
+#define FW_CFG_DMA_CTL_ERROR   0x01
+#define FW_CFG_DMA_CTL_READ    0x02
+#define FW_CFG_DMA_CTL_SKIP    0x04
+#define FW_CFG_DMA_CTL_SELECT  0x08
+#define FW_CFG_DMA_CTL_WRITE   0x10
+
+#define FW_CFG_DMA_SIGNATURE 0x51454d5520434647ULL /* "QEMU CFG" */
+
+#define BIOS_CFG_DMA_ADDR_HIGH  0x514
+#define BIOS_CFG_DMA_ADDR_LOW   0x518
+
 /* Break the translation block flow so -d cpu shows us values */
 #define DEBUG_HERE \
        jmp             1f;                             \
@@ -62,6 +73,72 @@
        bswap           %eax
 .endm
 
+
+/*
+ * Read data from the fw_cfg device using DMA.
+ * Clobbers:   %eax, %edx, memory[%esp-16] to memory[%esp]
+ */
+.macro read_fw_dma VAR, SIZE, ADDR
+       movl            $\VAR, %eax /* Control */
+       shl             $16, %eax
+       or              $FW_CFG_DMA_CTL_READ, %eax
+       or              $FW_CFG_DMA_CTL_SELECT, %eax
+       bswapl          %eax
+       movl            %eax, -16(%esp)
+
+       movl            \SIZE, %eax /* Length */
+       bswapl          %eax
+       mov             %eax, -12(%esp)
+
+       mov             \ADDR, %eax /* Address to write to */
+       bswapl          %eax
+       mov             %eax, -4(%esp)
+
+       movl            $0, %eax  /* We only support 32 bit target addresses */
+       mov             %eax, -8(%esp)
+
+       mov             %esp, %eax /* Address of the struct we generated */
+       subl            $16, %eax
+       bswapl          %eax
+
+       mov             $BIOS_CFG_DMA_ADDR_LOW, %dx
+       outl            %eax, (%dx) /* Initiate DMA */
+
+       movl            $FW_CFG_DMA_CTL_ERROR, %eax
+       not             %eax
+       bswapl          %eax
+
+1:  mov                -16(%esp), %edx /* Wait for completion */
+       and             %eax, %edx
+       jnz             1b
+.endm
+
+/*
+ * Read a single 32 bit value from the fw_cfg device using DMA
+ * Clobbers: %edx, memory[%esp-20] to memory[%esp]
+ * Out:                %eax
+ */
+.macro read_fw_dma_var32 VAR
+       mov             %esp, %edx
+       subl            $20, %edx
+       read_fw_dma     \VAR, $4, %edx
+       mov             -20(%esp), %eax
+.endm
+
+
+/*
+ * Read a blob from the fw_cfg device using DMA
+ * Requires _ADDR, _SIZE and _DATA values for the parameter.
+ *
+ * Clobbers:   %eax, %edx, %es, %ecx, %edi and adresses %esp-20 to %esp
+ */
+#define read_fw_blob_dma(var) \
+       read_fw_dma_var32       var ## _SIZE; \
+       mov             %eax, %ecx; \
+       read_fw_dma_var32       var ## _ADDR; \
+       mov             %eax, %edi ;\
+       read_fw_dma     var ## _DATA, %ecx, %edi
+
 #define read_fw_blob_pre(var)                          \
        read_fw         var ## _SIZE;                   \
        mov             %eax, %ecx;                     \
-- 
2.33.0