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Re: [Qemu-devel] [PATCH v2] memory: Introduce DEVICE_HOST_ENDIAN for ram
From: |
Alexey Kardashevskiy |
Subject: |
Re: [Qemu-devel] [PATCH v2] memory: Introduce DEVICE_HOST_ENDIAN for ram device |
Date: |
Tue, 28 Feb 2017 12:04:26 +1100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 |
On 28/02/17 11:41, David Gibson wrote:
> On Mon, Feb 27, 2017 at 12:52:44PM +0800, Yongji Xie wrote:
>> At the moment ram device's memory regions are DEVICE_NATIVE_ENDIAN. It's
>> incorrect. This memory region is backed by a MMIO area in host, so the
>> uint64_t data that MemoryRegionOps read from/write to this area should be
>> host-endian rather than target-endian. Hence, current code does not work
>> when target and host endianness are different which is the most common case
>> on PPC64. To fix it, this introduces DEVICE_HOST_ENDIAN for the ram device.
>>
>> This has been tested on PPC64 BE/LE host/guest in all possible combinations
>> including TCG.
>>
>> Suggested-by: Paolo Bonzini <address@hidden>
>> Signed-off-by: Yongji Xie <address@hidden>
>
> Reviewed-by: David Gibson <address@hidden>
>
> The effect of the patch is certainly correct. I remain a little
> concerned that the name "host endian" might cause more confusion than
> it resolves, but a better term isn't immediately obvious to me.
In order to match memory_region_wrong_endianness(), it could be
DEVICE_CORRECT_ENDIAN :)
Just joking :)
>
>> ---
>> include/exec/cpu-common.h | 6 ++++++
>> memory.c | 2 +-
>> 2 files changed, 7 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
>> index bd15853..eef74df 100644
>> --- a/include/exec/cpu-common.h
>> +++ b/include/exec/cpu-common.h
>> @@ -36,6 +36,12 @@ enum device_endian {
>> DEVICE_LITTLE_ENDIAN,
>> };
>>
>> +#if defined(HOST_WORDS_BIGENDIAN)
>> +#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN
>> +#else
>> +#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN
>> +#endif
>> +
>> /* address in the RAM (different from a physical address) */
>> #if defined(CONFIG_XEN_BACKEND)
>> typedef uint64_t ram_addr_t;
>> diff --git a/memory.c b/memory.c
>> index ed8b5aa..17cfada 100644
>> --- a/memory.c
>> +++ b/memory.c
>> @@ -1180,7 +1180,7 @@ static void memory_region_ram_device_write(void
>> *opaque, hwaddr addr,
>> static const MemoryRegionOps ram_device_mem_ops = {
>> .read = memory_region_ram_device_read,
>> .write = memory_region_ram_device_write,
>> - .endianness = DEVICE_NATIVE_ENDIAN,
>> + .endianness = DEVICE_HOST_ENDIAN,
>> .valid = {
>> .min_access_size = 1,
>> .max_access_size = 8,
>
--
Alexey
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