Re: [Xen-devel] [PATCH v4 2/2] IB/qib: use arch_phys_wc_add()

[Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>]

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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