Commit 2cc06a88 authored by Kevin O'Connor's avatar Kevin O'Connor Committed by Gerd Hoffmann
Browse files

fw_cfg: Define a static signature to be returned on DMA port reads 



Return a static signature ("QEMU CFG") if the guest does a read to the
DMA address io register.

Signed-off-by: default avatarKevin O'Connor <kevin@koconnor.net>
Reviewed-by: default avatarLaszlo Ersek <lersek@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
parent c886fc4c

docs/specs/fw_cfg.txt

+3 −0
Original line number Diff line number Diff line
@@ -93,6 +93,9 @@ by selecting the "signature" item using key 0x0000 (FW_CFG_SIGNATURE), 
and reading four bytes from the data register. If the fw_cfg device is

present, the four bytes read will contain the characters "QEMU".



If the DMA interface is available, then reading the DMA Address

Register returns 0x51454d5520434647 ("QEMU CFG" in big-endian format).



=== Revision / feature bitmap (Key 0x0001, FW_CFG_ID) ===



A 32-bit little-endian unsigned int, this item is used to check for enabled

hw/nvram/fw_cfg.c

+12 −2
Original line number Diff line number Diff line
@@ -53,6 +53,8 @@ 
#define FW_CFG_DMA_CTL_SKIP    0x04

#define FW_CFG_DMA_CTL_SELECT  0x08



#define FW_CFG_DMA_SIGNATURE 0x51454d5520434647ULL /* "QEMU CFG" */



typedef struct FWCfgEntry {

    uint32_t len;

    uint8_t *data;
@@ -397,6 +399,13 @@ static void fw_cfg_dma_transfer(FWCfgState *s) 
    trace_fw_cfg_read(s, 0);

}



static uint64_t fw_cfg_dma_mem_read(void *opaque, hwaddr addr,

                                    unsigned size)

{

    /* Return a signature value (and handle various read sizes) */

    return extract64(FW_CFG_DMA_SIGNATURE, (8 - addr - size) * 8, size * 8);

}



static void fw_cfg_dma_mem_write(void *opaque, hwaddr addr,

                                 uint64_t value, unsigned size)

{
@@ -420,7 +429,7 @@ static void fw_cfg_dma_mem_write(void *opaque, hwaddr addr, 
static bool fw_cfg_dma_mem_valid(void *opaque, hwaddr addr,

                                  unsigned size, bool is_write)

{

    return is_write && ((size == 4 && (addr == 0 || addr == 4)) ||

    return !is_write || ((size == 4 && (addr == 0 || addr == 4)) ||

                         (size == 8 && addr == 0));

}
@@ -492,6 +501,7 @@ static const MemoryRegionOps fw_cfg_comb_mem_ops = { 
};



static const MemoryRegionOps fw_cfg_dma_mem_ops = {

    .read = fw_cfg_dma_mem_read,

    .write = fw_cfg_dma_mem_write,

    .endianness = DEVICE_BIG_ENDIAN,

    .valid.accepts = fw_cfg_dma_mem_valid,