Re: [Qemu-devel] [PATCH v4] Add optionrom compatible with fw_cfg DMA version

[Gerd Hoffmann <kraxel@redhat.com>]

  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.

> 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?

cheers,
  Gerd