[illumos-Developer] Webrev #534: DMA KVA cache attributes incorrect

[Garrett D'Amore]

On Tue, 2011-05-10 at 11:21 -0400, Albert Lee wrote:
> First obvious problem is that this always clears the documented cache
> flags for ddi_dma_mem_alloc(9) and only uses the attributes in
> ddi_device_acc_attr->devacc_attr_dataorder.
> 
> The cache attributes there are explicitly "advisory, not mandatory".

Nice catch.  And yes, on SPARC, they can't be used.

So perhaps only set these flags if they weren't passed in already?

	- Garrett

> 
> On Tue, May 10, 2011 at 11:05 AM, Michael Tsymbalyuk <mtzaurus at gmail.com> wrote:
> >  For test purposes I added a code snipped to the vmxnet3.c
> > driver (for my local testing purposes, of course) - since
> > we need a real device for dealing with DMA memory allocation.
> > Inside device's attach() logic it allocates 3 DMA areas with different
> > attributes:
> >
> >   "DDI_STRICTIRDER_ACC",
> >   "DDI_MERGING_OK_ACC",
> >   "DDI_UNORDERED_OK_ACC"
> >
> >  and prints out their addresses.
> >
> > Next, I run mdb -k and walk through these addresses using ::vatopfn
> > and ::pte commands.
> >
> > It shows that areas have the following attributes:
> >
> >    DDI_STRICTIRDER_ACC : uncached
> >    DDI_MERGING_OK_ACC  : wrcombine
> >    DDI_UNORDERED_OK_ACC : <no caching attributes>
> >
> > Sincerely,
> > Michael Tsymbalyuk
> >
> >> On Tue, 2011-05-10 at 18:08 +0400, Michael Tsymbalyuk wrote:
> >> > Thiw webrev fixes the problem of improper handling of page table
> >> > attributes related to caching while allocating a DMA-compatible
> >> > memory via ddi_dma_mem_alloc(). The patch adds extra attribute check
> >> > to ddi_dma_mem_alloc().
> >> >
> >> > http://cr.illumos.org/view/asjt99s5/illumos-534-webrev/
> >> >
> >> > Sincerely,
> >> > Michael Tsymbalyuk
> >> >
> >>
> >> This looks good if it is that simple.  I want to do some deeper analysis
> >> to review your code.  Out of curiosity, did you test this at all?  If
> >> so, how?
> >>
> >>       - Garrett
> >> >
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> >>
> >
> >
> >
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