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Re: [Qemu-ppc] [PATCH 14/25] spapr: push the XIVE EQ data in OS event qu

From: Cédric Le Goater
Subject: Re: [Qemu-ppc] [PATCH 14/25] spapr: push the XIVE EQ data in OS event queue
Date: Tue, 5 Dec 2017 10:58:23 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 12/04/2017 01:20 AM, David Gibson wrote:
> On Sat, Dec 02, 2017 at 08:46:19AM -0600, Benjamin Herrenschmidt wrote:
>> On Sat, 2017-12-02 at 08:45 -0600, Benjamin Herrenschmidt wrote:
>>> On Fri, 2017-12-01 at 15:10 +1100, David Gibson wrote:
>>>> Hm, ok.  Guest endian (or at least, not definitively host-endian) data
>>>> in a plain uint32_t makes me uncomfortable.  Could we use char data[4]
>>>> instead, to make it clear it's a byte-ordered buffer, rather than a
>>>> number as far as the XIVE is concerned.
>>>> Hm.. except that doesn't quite work, because the hardware must define
>>>> which end that generation bit ends up in...
>>> It also needs to be written atomically. Just say it's big endian.
>> Also the guest reads it using be32_to_cpup...
> Ok.  Definitely should be treated as BE and read/written with the be32
> DMA helper functions.

hmm, the stl_be_dma does not return errors but dma_memory_write()

    static inline void st##_sname##_##_end##_dma(AddressSpace *as,      \
                                                 dma_addr_t addr,       \
                                                 uint##_bits##_t val)   \
    {                                                                   \
        val = cpu_to_##_end##_bits(val);                                \
        dma_memory_write(as, addr, &val, (_bits) / 8);                  \

These macros seem to be only used by spapr_vio and nvram. I can probably 
change them.


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