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Re: [Qemu-devel] [PATCHv2] fw_cfg: Define a static signature to be retur
From: |
Kevin O'Connor |
Subject: |
Re: [Qemu-devel] [PATCHv2] fw_cfg: Define a static signature to be returned on DMA port reads |
Date: |
Tue, 6 Oct 2015 10:29:25 -0400 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Tue, Oct 06, 2015 at 09:30:18AM +0200, Laszlo Ersek wrote:
> On 10/06/15 01:51, Kevin O'Connor wrote:
> > Return a static signature ("QEMU CFG") if the guest does a read to the
> > DMA address io register.
> >
> > Signed-off-by: Kevin O'Connor <address@hidden>
> > ---
> >
> > Marc, if you decide to respin your fw_cfg series, I've updated the dma
> > signature patch. This addresses the comments from Stefan, and I hope
> > it addresses the comments from Laszlo.
>
> Thank you -- I didn't know about extract64().
>
> The patch looks good to me, but I think the QEMU coding style requries
> /* ... */ comments, and forbids //.
I always forget about that one. Marc, if you do respin the series I
updated the patch below.
-Kevin
commit 02a449ece95da00fa64a9c704555c6afa8e03579
Author: Kevin O'Connor <address@hidden>
Date: Thu Oct 1 14:16:59 2015 +0200
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.
Reviewed-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Kevin O'Connor <address@hidden>
diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
index 2d6b2da..cbdce7d 100644
--- a/docs/specs/fw_cfg.txt
+++ b/docs/specs/fw_cfg.txt
@@ -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
diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 59933b3..5098bfc 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -53,6 +53,8 @@
#define FW_CFG_DMA_CTL_SKIP 0x04
#define FW_CFG_DMA_CTL_SELECT 0x08
+#define FW_CFG_DMA_SIGNATURE 0x51454d5520434647 /* "QEMU CFG" */
+
typedef struct FWCfgEntry {
uint32_t len;
uint8_t *data;
@@ -393,6 +395,13 @@ 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)
{
@@ -416,8 +425,8 @@ 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)) ||
- (size == 8 && addr == 0));
+ return !is_write || ((size == 4 && (addr == 0 || addr == 4)) ||
+ (size == 8 && addr == 0));
}
static bool fw_cfg_data_mem_valid(void *opaque, hwaddr addr,
@@ -488,6 +497,7 @@ 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,