[Bug] VCHIQ functional test broken
Russell King - ARM Linux
linux at armlinux.org.uk
Sat May 13 02:30:16 PDT 2017
On Sat, May 13, 2017 at 11:07:28AM +0200, Stefan Wahren wrote:
> In the meantime this issue has been fixed by Phil .
Right - definitely a driver bug. Mapping more memory for DMA than is
actually going to be DMA'd to and expecting data to be preserved is
> Unfortunately i found another issue. If i enable CONFIG_HIGHMEM in
> the kernel config, the data during functional test gets corrupted.
> Phil said it's caused by the usage of get_user_pages() .
Without knowing who "Phil" is in that thread, but...
HIGHMEM is a problem because you can't use get_user_pages on pages in
is an interesting statement, and without any reasoning or evidence.
I also believe it to be incorrect. get_user_pages() returns an array
of struct page pointers for the user memory, calling flush_dcache_page()
and flush_anon_page() on them to ensure that any kernel mapping is
coherent with what is in userspace.
As far as returning the array of page pointers, get_user_pages() doesn't
care whether they're lowmem or highmem.
flush_dcache_page() doesn't care either - if it wants to flush the page
and the page is a highmem page, it will temporarily map it before
flush_anon_page() is a no-op for all non-aliasing caches.
get_user_pages() works fine for whatever memory on other platforms and
drivers such as etnaviv, so I think this comes down to the vchip driver
doing things in ways that the kernel interfaces its using don't expect -
exactly like the "lets pass full pages to the DMA API" broken-ness.
I would like to hear the justification for that statement, but without
any justification, I assert that the statement is false.
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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