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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,



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