Hi Christoph, Andy
On 03/27/2018 11:11 AM, Andy Shevchenko wrote:
On Tue, Mar 27, 2018 at 8:12 PM, Evgeniy Didin
<evgeniy.di...@synopsys.com> wrote:
Hello,
After commit 57bf5a8963f8 ("dma-mapping: clear harmful GFP_* flags in common
code") we noticed problems with Ethernet controller on one of our platforms (namely
ARC HSDK).
I
n particular we see that removal of __GFP_ZERO flag in function
dma_alloc_attrs() was the culprit because in our implementation of
arc_dma_alloc() we only allocate zeroed pages if
that flag is explicitly set by the caller. Now with unconditional removal of
that flag in dma_alloc_attrs() we allocate non-zeroed pages and that seem to
cause problems.
From
mentioned commit message I may conclude that architectural code is supposed to
always allocate zeroed pages but I cannot find any requirement of that in
kernel's documentation.
Coul
d you please point me to that requirement if that exists at all, then we'll
implement a fix in our arch code like that:
[snip]
Another question why caller can't ask for zero pages explicitly?
Question to whom ? The caller can ask for it - but the problem here is generic dma
API code is clearing out GFP_ZERO and expecting arch code to memst unconditionally
- is that expected of arch code - and is documented ?
That is broken to begin with - arch dma_alloc* simply passes thru gfp flags to
page allocator and doesn't muck around with them. We could in theory but doesn't
seem like the right thing to do IMO.
-Vineet
