Re: [PATCH] dmaengine: rcar-dmac: Handle hardware descriptor allocation failure

From: Vinod Koul
Date: Tue Dec 09 2014 - 01:39:04 EST

On Mon, Dec 08, 2014 at 11:20:44PM +0530, Vinod Koul wrote:
> On Mon, Dec 08, 2014 at 07:40:15PM +0200, Laurent Pinchart wrote:
> > > > [GIT PULL FOR v3.19] R-Car DMA engine driver
> > > >
> > >
> > > And I dont seem to have this request in my Inbox :(
> > > Yes I do see it in archieves, so not sure how this is not present, not sure
> > > if the servers mangeled it!!
> >
> > I haven't CC'ed you, I'll make sure to do so next time. The mail should still
> > have reached you through the mailing list though (I assume you're subscribed
> > to dmaengine@xxxxxxxxxxxxxxx ;-)).
> Yes I am, so should have reached me even though i wasnt cced
> I do see email reaching me from list without me being in CC, but then it
> wont hit my inbox and go to ML folder :)
> So generally its a good practice to CC relvant folks, lots of folks do ask
> that if ML is high volume

Hey Laurent,

I see that the oddity in commitlogs with change since artifacts after SOB,
can you please fix that up

commit 43dc9ba2b51ccb9124bf6fed614c5053500592a6
Author: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
Date: Sat Jul 19 00:05:14 2014 +0200

dmaengine: rcar-dmac: Cache hardware descriptors memory

Unlike DMA transfers descriptors that are preallocated and cached,
memory used to store hardware descriptors is allocated and freed with
the DMA coherent allocation API for every transfer. Besides degrading
performances, this creates a CMA stress test that seems to cause issues.
Running dmatest with the noverify option produces

[ 50.066539] alloc_contig_range test_pages_isolated(6b845, 6b846) failed
[ 50.235180] alloc_contig_range test_pages_isolated(6b848, 6b84e) failed
[ 52.964584] alloc_contig_range test_pages_isolated(6b847, 6b848) failed
[ 54.127113] alloc_contig_range test_pages_isolated(6b843, 6b844) failed
[ 56.270253] alloc_contig_range test_pages_isolated(6b84c, 6b850) failed

The root cause needs to be fixed, but in the meantime, as a workaround
and a performance improvement, cache hardware descriptors.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
Tested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>


Changes since v2:

- Typo fixes
- Align allocated hwdesc size to page size
- Ignore allocated hwdesc memory when the transfer doesn't use hwdescs

commit feb2e9f12b1a4a871b1d3eb2e2f44255510a79d3
Author: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
Date: Wed Jul 16 23:15:48 2014 +0200

dmaengine: rcar-dmac: Implement support for hardware descriptor lists

The DMAC supports hardware-based auto-configuration from descriptor
lists. This reduces the number of interrupts required for processing a
DMA transfer. Support that mode in the driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
Tested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>


Changes since v2:

- Typo fixes
- Use GFP_NOWAIT to allocate hardware descriptors
- Clear descriptor stage end interrupt when halting the channel

and many more...


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