linux-kernel - Re: [PATCH] STAGING: Comedi: Build only on arches providing PAGE_KERNEL

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Date:	Fri, 24 Jun 2011 09:55:42 +1000
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	linux-m32r@...linux-m32r.org, linux-m32r-ja@...linux-m32r.org,
	linux-am33-list@...hat.com, Paul Mundt <lethal@...ux-sh.org>,
	linux-sh@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] STAGING: Comedi: Build only on arches providing
 PAGE_KERNEL_NOCACHE

Hi Ralf,

On Thu, 23 Jun 2011 12:45:37 +0100 Ralf Baechle <ralf@...ux-mips.org> wrote:
>
> On architectures that don't define PAGE_KERNEL_NOCACHE, the Comedi driver turns
> into tragedy:
> 
>   CC [M]  drivers/staging/comedi/drivers.o
> drivers/staging/comedi/drivers.c: In function ‘comedi_buf_alloc’:
> drivers/staging/comedi/drivers.c:505:41: error: ‘PAGE_KERNEL_NOCACHE’ undeclared (first use in this function)
> drivers/staging/comedi/drivers.c:505:41: note: each undeclared identifier is rep orted only once for each function it appears in
> make[3]: *** [drivers/staging/comedi/drivers.o] Error 1
> 
> Restrict the driver to only those architectures that define PAGE_KERNEL_NOCACHE.
> 
> PAGE_KERNEL_NOCACHE is a kludge - some system architectures such as SGI IP27
> are even uable to offer uncached operation - at least in the way an unwitting
> driver might assume.  I haven't looked in details how the driver is using
> the area vmaped with PAGE_KERNEL_NOCACHE but maybe doing it XFS-style using
> cached memory and the flush_kernel_vmap_range / invalidate_kernel_vmap_range
> APIs in conjunction with the DMA API is a practical alternative.
> 
> Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>

Since Greg is on vacation, I will add this patch to my fixes tree in
linux-next until a better fix comes along (if there is one).

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au
http://www.canb.auug.org.au/~sfr/

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