[illumos-Developer] vmxnet3s driver failing on debug builds due to dma_attr_sgllen == -1 (Bug #422)

[Garrett D'Amore]

I've finally looked at this.  I agree, its a bug for DEBUG kernels.
Lets file a bug in illumos, and we'll fix it.

	- Garrett

On Sat, 2011-02-05 at 23:19 -0600, Mike La Spina wrote:
> I would think that the debug call code is not appropriate. There is
> nothing wrong with the -1 value and it should not return a bad attribute
> when it's valid.
> 
> -----Original Message-----
> From: Yuri Pankov [mailto:yuri.pankov at gmail.com] 
> Sent: Saturday, February 05, 2011 10:54 AM
> To: Garrett D'Amore
> Cc: developer at lists.illumos.org
> Subject: Re: [illumos-Developer] vmxnet3s driver failing on debug builds
> due to dma_attr_sgllen == -1 (Bug #422)
> 
> On Sat, Feb 05, 2011 at 07:34:56AM -0800, Garrett D'Amore wrote:
> > On Sat, 2011-02-05 at 10:29 +0300, Yuri Pankov wrote:
> > > Hi,
> > > 
> > > While looking into the issue, I've found the following piece of code
> in
> > > usr/src/uts/i86pc/io/rootnex.c, called only in debug builds:
> > > 
> > > /*
> > >  * rootnex_valid_alloc_parms()
> > >  *    Called in ddi_dma_alloc_handle path to validate its
> parameters.
> > >  */
> > > static int
> > > rootnex_valid_alloc_parms(ddi_dma_attr_t *attr, uint_t
> maxsegmentsize)
> > > ...
> > >         if ((attr->dma_attr_seg & MMU_PAGEOFFSET) != MMU_PAGEOFFSET
> ||
> > >             MMU_PAGESIZE & (attr->dma_attr_granular - 1) ||
> > > ==>         attr->dma_attr_sgllen <= 0) {          <===
> > >                 return (DDI_DMA_BADATTR);
> > >         }
> > > ...
> > > 
> > > vmxnet3s driver uses dma_attr_sgllen == -1, which is pretty ok
> according
> > > to ddi_dma_attr(9S):
> > > ...
> > >      < 0    Device DMA engine is not constrained by the size, for
> > >             example, withDMA chaining.
> > > ...
> > > 
> > > Removing the check allows the driver to successfully start (and
> > > function, I haven't tested the 10Gbps speed due to the lack of
> hardware,
> > > but currently finishing 50GB transfer at 1Gbps speed). The check is
> > > there from the OpenSolaris launch, so the my real question is - what
> of
> > > the following sounds correct:
> > > - the check is bogus and should be removed (or changed to == 0,
> which is
> > >   reserved per manpage)
> > > or
> > > - documentation (ddi_dma_attr(9S), at least) should be updated and
> the
> > >   driver should be "fixed".
> > > 
> > 
> > I haven't looked yet, but lots of drivers have sgllen == -1.  That
> means
> > your driver can accept arbitrary chaining via linked lists.  I expect
> > there is something else going on here, and I'll look at more closely
> as
> > soon as I have time.
> > 
> > 	- Garrett
> 
> Thanks Garrett.
> 
> I just wasn't able to find any driver in tree using sgllen = -1 (that
> was just some grepping though) and I don't really see how allocation
> could succeed given the codepath. Could you please provide some examples
> of drivers using sgllen = -1? Sorry if I'm missing something obvious
> here, have much to learn yet..
> 
> 
> TIA,
> Yuri
> 
> _______________________________________________
> Developer mailing list
> Developer at lists.illumos.org
> http://lists.illumos.org/m/listinfo/developer