linux-kernel - Re: [Intel-gfx] [PATCH 06/13] drm: add helper to clflush a virtual address range

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Date:	Mon, 21 Nov 2011 11:46:49 -0800
From:	Ben Widawsky <ben@...dawsk.net>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 06/13] drm: add helper to clflush a virtual
 address range

On Sun, Nov 06, 2011 at 08:13:53PM +0100, Daniel Vetter wrote:
> Useful when the page is already mapped to copy date in/out.
> 
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
> ---
>  drivers/gpu/drm/drm_cache.c |   23 +++++++++++++++++++++++
>  include/drm/drmP.h          |    1 +
>  2 files changed, 24 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
> index 0e3bd5b..502771a 100644
> --- a/drivers/gpu/drm/drm_cache.c
> +++ b/drivers/gpu/drm/drm_cache.c
> @@ -97,3 +97,26 @@ drm_clflush_pages(struct page *pages[], unsigned long num_pages)
>  #endif
>  }
>  EXPORT_SYMBOL(drm_clflush_pages);
> +
> +void
> +drm_clflush_virt_range(char *addr, unsigned long length)
> +{
> +#if defined(CONFIG_X86)
> +	if (cpu_has_clflush) {
> +		char *end = addr + length;
> +		mb();
> +		for (; addr < end; addr += boot_cpu_data.x86_clflush_size)
> +			clflush(addr);
> +		clflush(end - 1);
> +		mb();
> +		return;
> +	}
> +
> +	if (on_each_cpu(drm_clflush_ipi_handler, NULL, 1) != 0)
> +		printk(KERN_ERR "Timed out waiting for cache flush.\n");
> +#else
> +	printk(KERN_ERR "Architecture has no drm_cache.c support\n");
> +	WARN_ON_ONCE(1);
> +#endif
> +}
> +EXPORT_SYMBOL(drm_clflush_virt_range);

I'd feel more comfortable with a BUG_ON(irqs_disabled()); before the
IPI... though I don't even know how many platforms that actually
pertains to (if any).
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