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Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensi

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive
Date: Thu, 23 Feb 2017 10:23:33 +0000

On 23 February 2017 at 10:10, Paolo Bonzini <address@hidden> wrote:
> On 23/02/2017 11:02, Peter Maydell wrote:
>> I'm really not convinced we need DEVICE_HOST_ENDIAN. RAM
>> areas should be target-endian (you can probably define
>> "target endianness" as "the endianness that RAM areas have".)
> This is not RAM.  This is MMIO, backed by a MMIO area in the host.

Hmm, I see...the naming is a bit unfortunate if it's not RAM.

> The
> MemoryRegionOps read from the MMIO area (so the data has host
> endianness) and do not do any further swap:
>         data = *(uint16_t *)(mr->ram_block->host + addr);
> Here, the dereference is basically the same as ldl_he_p.
> If you wanted to make the MemoryRegion use DEVICE_NATIVE_ENDIAN, you'd
> need to tswap around the access.  Or you can use ldl_le_p and
> DEVICE_LITTLE_ENDIAN (this is what Yongji's patch open codes), or
> ldl_be_p and DEVICE_BIG_ENDIAN.  They are all the same in the end.

Using stl_p &c in a DEVICE_NATIVE_ENDIAN MR would work too, right?
(This is how all the NATIVE_ENDIAN MRs in exec.c work.)

-- PMM

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