Re: [PATCH] ArmPlatformPkg: remove EFI_MEMORY_UC attribute from normal memory

[Leif Lindholm <leif.lindholm@linaro.org>]

On Thu, Sep 08, 2016 at 05:37:13PM +0000, Cohen, Eugene wrote:
> > I think this is the right thing to do; Arguably, on the modern ARM
> > architectures, UNCACHEABLE and WRITE_COMBINEABLE are mutually
> > exclusive. I'll discuss with Charles whether we should codify this in
> > the UEFI specification.
> 
> Given the corresponding X86 semantics it makes sense for UNCACHEABLE
> to map to Strongly Ordered and WRITE_COMBINEABLE to map to "Normal"
> Uncacheable.   It's useful to expose this separately in case a DMA
> common buffer has semantics that require the strongly ordered
> behavior.
> 
> Since this is providing a list of capabilities I'm not sure what the
> statement about mutual exclusivity refers to.

Do note the weasly "arguably" I stuck in there.

My point is basically the same as yours, with the clarification that
for purposes of treating something like general-purpose memory,
flagging a location as possible to map as either UNCACHEABLE (ARM:
Strongly Ordered) or WRITE_COMBINEABLE (ARM: Normal uncached)
generally does not make sense.

Regards,

Leif