Re: [Xen-devel] [PATCH 13/45] xen: arm64: dcache flush

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-02-07 at 16:14 +0000, Tim Deegan wrote:
> At 15:56 +0000 on 23 Jan (1358956579), Ian Campbell wrote:
> > This drops the
> >     "m" (*_p)
> > asm contraint. I can't figure out what this was for.
> > 
> 
> It's to stop the compiler hoisting writes to the wrong side of the
> flush.  It's the lighter-weight equivalent to the "memory" clobber in
> the range version.  By moving from inline "dsb;" to dsb() you've
> reintroduced the full memory clobber here anyway. :(

Ah, I forgot about the "memory" on the inline asm of the dsb macro.

How about #define _dsb() __asm__ __volatile__ ("dsb" : : :)
for cases such as this?

I think on 32-bit "dsb" == "dsb sy", while on 64-bit only the "dsb sy"
form is valid. The reason I didn't err on the side of just adding the
"sy" was that often there is something else which differs between the
two in the same asm inline block and so using the macro throughout
seemed cleaner. Perhaps I should rethink this.

Ian.


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