From: "Jiang, Dave" <dave.jiang@intel.com>
To: Brice Goglin <Brice.Goglin@inria.fr>
CC: "Mason, Jon" <jon.mason@intel.com>, Dan Williams <djbw@fb.com>,
        "Koul, Vinod" <vinod.koul@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: ioatdma: add ioat_raid_enabled module parameter
Thread-Topic: ioatdma: add ioat_raid_enabled module parameter
Thread-Index: AQHOjjom0XMeyUNRoUmcakeh/vzoC5l/z3CAgAE92oCAAAEvgIAA7+UAgACRWYA=
Date: Fri, 2 Aug 2013 16:14:49 +0000
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	  <20130801171144.GB13747@jonmason-lab>
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That looks fine. 
Acked-by: Dave Jiang <dave.jiang@intel.com>

On Fri, 2013-08-02 at 09:34 +0200, Brice Goglin wrote:
> Le 01/08/2013 19:15, Jiang, Dave a écrit :
> > 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. 
> >
> 
> Here's a patch that may do what you guys are saying.
> 
> Brice
> 
> 
> 
> ioatdma: disable RAID by default when buggy and add module param
> 
> Commit f26df1a1 added a 64-byte alignment requirement for legacy
> operations to work around a silicon errata when mixing legacy and
> RAID descriptors.
> 
> RAID offload is now disabled by default on buggy 3.2 platforms.
> Passing ioat_raid_enabled=1 force-enables it on all platforms
> (previous behavior).
> Passing ioat_raid_enabled=0 force-disables it everywhere.
> 
> When RAID offload is disabled, legacy operations (memcpy, etc.)
> can work again without alignment restrictions.
> 
> Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
> ---
>  drivers/dma/ioat/dma_v3.c |   16 ++++++++++++++--
>  1 file changed, 14 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	2013-08-02 09:28:51.817037742 +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 (-1=enabled unless broken [default], 0=disabled, 1=enabled)");
> +
>  /* 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 (ioat_raid_enabled == 1 && is_xeon_cb32(pdev))
>  		dma->copy_align = 6;
>  
>  	dma_cap_set(DMA_INTERRUPT, dma->cap_mask);
> @@ -1783,7 +1788,14 @@ int ioat3_dma_probe(struct ioatdma_devic
>  
>  	device->cap = readl(device->reg_base + IOAT_DMA_CAP_OFFSET);
>  
> -	if (is_bwd_noraid(pdev))
> +	/* disable RAID if:
> +	 *    force-disabled by module param,
> +	 * or not force-enabled on buggy 3.2 platforms,
> +	 * or not actually supported.
> +	 */
> +	if (ioat_raid_enabled == 0
> +	    || (ioat_raid_enabled != 1 && is_xeon_cb32(pdev))
> +	    || 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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