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From: Laszlo Ersek <lersek@redhat.com>
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Date: Wed, 3 Feb 2016 12:48:59 +0100
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Subject: Re: [Qemu-devel] [PATCH v4] Add optionrom compatible with fw_cfg
 DMA version
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: =?UTF-8?Q?Marc_Mar=c3=ad?= <marc.mari.barcelo@gmail.com>, "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Kevin O'Connor <kevin@koconnor.net>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, =?UTF-8?Q?Marc_Mar=c3=ad?= <markmb@redhat.com>

On 02/03/16 09:44, Gerd Hoffmann wrote:
>   Hi,
> 
>> I think the "dma_enabled" property is not exposed to the user.
> 
> It is: "-global fw_cfg.dma_enabled=off" works (as in: doesn't throw an
> error).  Has no effect through as it gets overridden later on.
> 
>> The default value of "dma_enabled" in both fw_cfg_io_properties and
>> fw_cfg_mem_properties is irrelevant; the actual property value is always
>> overwritten in fw_cfg_init_io_dma() and fw_cfg_init_mem_wide(), which
>> all of the init paths go through.
> 
> And IMHO we should not do that, so setting the property actually has an
> effect.

Fair point.

>> I agree that DMA capability should be filtered with machine type.
>> However, that distinction should not be made using the current
>> "dma_enabled" properties (i.e., of "fw_cfg_io_properties" and
>> "fw_cfg_mem_properties". Instead, it should be made in the
>> board-specific callers of fw_cfg_init_(io_dma|mem_wide).
> 
> Why?

That's how "has_reserved_memory" works as well, for example.

But, if the property is made work, I guess PC_COMPAT_2_4 can be used
too. (Or should it be HW_COMPAT_2_4?)

Is that your point?

Thanks
Laszlo