Re: ioatdma: add ioat_raid_enabled module parameter

["Jiang, Dave" <dave.jiang@intel.com>]

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On Thu, 2013-08-01 at 10:11 -0700, Jon Mason wrote:
> On Wed, Jul 31, 2013 at 03:14:07PM -0700, Jiang, Dave wrote:
> > I'm ok with enabling this for people that just want to use DMA and not
> > RAID. 
> 
> I might be crazy, but I'd be in favor of disabling the RAID offload by
> default on non-Atom platforms.
> 

I suppose. Technically it is disabled starting with 3.10 because of the
channel switch issue. I'm ok with this disabled by default for the 3.2
platforms that has broken pq-val. 

> Thanks,
> Jon
> 
> > 
> > Acked-by: Dave Jiang <dave.jiang@intel.com>
> > 
> > On Thu, 2013-08-01 at 00:05 +0200, Brice Goglin wrote:
> > > ioatdma: add ioat_raid_enabled module parameter
> > > 
> > > Commit f26df1a1 added a 64-byte alignment requirement for legacy
> > > operations to work around a silicon errata when mixing legacy and
> > > RAID descriptors.
> > > Passing ioat_raid_enabled=0 now disables RAID offload entirely in
> > > the ioatdma driver so that legacy operations (memcpy, etc.) can
> > > work without alignment restrictions anymore.
> > > 
> > > Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
> > > ---
> > >  drivers/dma/ioat/dma_v3.c |    9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > 
> > > Index: b/drivers/dma/ioat/dma_v3.c
> > > ===================================================================
> > > --- a/drivers/dma/ioat/dma_v3.c	2013-07-31 23:06:24.163810000 +0200
> > > +++ b/drivers/dma/ioat/dma_v3.c	2013-07-31 23:47:54.246719841 +0200
> > > @@ -67,6 +67,11 @@
> > >  #include "dma.h"
> > >  #include "dma_v2.h"
> > >  
> > > +static int ioat_raid_enabled = 1;
> > > +module_param(ioat_raid_enabled, int, 0444);
> > > +MODULE_PARM_DESC(ioat_raid_enabled,
> > > +		 "control support of RAID offload (default: 1)");
> > > +
> > >  /* ioat hardware assumes at least two sources for raid operations */
> > >  #define src_cnt_to_sw(x) ((x) + 2)
> > >  #define src_cnt_to_hw(x) ((x) - 2)
> > > @@ -1775,7 +1780,7 @@ int ioat3_dma_probe(struct ioatdma_devic
> > >  	dma->device_alloc_chan_resources = ioat2_alloc_chan_resources;
> > >  	dma->device_free_chan_resources = ioat2_free_chan_resources;
> > >  
> > > -	if (is_xeon_cb32(pdev))
> > > +	if (is_xeon_cb32(pdev) && ioat_raid_enabled)
> > >  		dma->copy_align = 6;
> > >  
> > >  	dma_cap_set(DMA_INTERRUPT, dma->cap_mask);
> > > @@ -1783,7 +1788,7 @@ int ioat3_dma_probe(struct ioatdma_devic
> > >  
> > >  	device->cap = readl(device->reg_base + IOAT_DMA_CAP_OFFSET);
> > >  
> > > -	if (is_bwd_noraid(pdev))
> > > +	if (!ioat_raid_enabled || is_bwd_noraid(pdev))
> > >  		device->cap &= ~(IOAT_CAP_XOR | IOAT_CAP_PQ | IOAT_CAP_RAID16SS);
> > >  
> > >  	/* dca is incompatible with raid operations */
> > > 
> > 

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