linux-kernel - Re: [PATCH v4 2/2] IB/qib: use arch_phys_wc

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Date:	Tue, 21 Apr 2015 16:17:18 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	infinipath@...el.com, roland@...nel.org, sean.hefty@...el.com,
	hal.rosenstock@...il.com, linux-rdma@...r.kernel.org,
	luto@...capital.net, mst@...hat.com, linux-kernel@...r.kernel.org,
	cocci@...teme.lip6.fr, "Luis R. Rodriguez" <mcgrof@...e.com>,
	Toshi Kani <toshi.kani@...com>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Roland Dreier <roland@...estorage.com>,
	Dennis Dalessandro <dennis.dalessandro@...el.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Juergen Gross <jgross@...e.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stefan Bader <stefan.bader@...onical.com>,
	konrad.wilk@...cle.com, ville.syrjala@...ux.intel.com,
	david.vrabel@...rix.com, jbeulich@...e.com,
	Roger Pau Monné <roger.pau@...rix.com>,
	linux-fbdev@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: [PATCH v4 2/2] IB/qib: use arch_phys_wc_add()

On Tue, Apr 21, 2015 at 02:50:35PM -0700, Luis R. Rodriguez wrote:
> -	if (qib_wc_pat) {
> -		resource_size_t vl15off;
> -		/*
> -		 * We do not set WC on the VL15 buffers to avoid
> -		 * a rare problem with unaligned writes from
> -		 * interrupt-flushed store buffers, so we need
> -		 * to map those separately here.  We can't solve
> -		 * this for the rarely used mtrr case.
> -		 */
> -		ret = init_chip_wc_pat(dd, 0);
> -		if (ret)
> -			goto bail;
> +	/*
> +	 * We do not set WC on the VL15 buffers to avoid
> +	 * a rare problem with unaligned writes from
> +	 * interrupt-flushed store buffers, so we need
> +	 * to map those separately here.  We can't solve
> +	 * this for the rarely used mtrr case.
> +	 */

This is a small change in behavior, but it doesn't seem important..

Mike, what do you think about adding:

 if (dd->wc_cookie)
    dev_err(.., "Using this device without CPU PAT support is known to be broken");

or similar..

Jason
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