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

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Message-Id: <8B77EED3-D197-4AB9-9594-278DB7002D6D@kernel.crashing.org>
Date:	Thu, 23 Jun 2011 07:10:29 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Martyn Welch <martyn.welch@...com>,
	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,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] STAGING: Comedi: Build only on arches providing PAGE_KERNEL_NOCACHE


On Jun 23, 2011, at 7:02 AM, Ralf Baechle wrote:

> On Thu, Jun 23, 2011 at 12:53:36PM +0100, Martyn Welch wrote:
> 
>> On 23/06/11 12:45, Ralf Baechle 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>
>>> 
>>> drivers/staging/comedi/Kconfig |    1 +
>>> 1 files changed, 1 insertions(+), 0 deletions(-)
>>> 
>>> diff --git a/drivers/staging/comedi/Kconfig b/drivers/staging/comedi/Kconfig
>>> index 1502d80..bccdc12 100644
>>> --- a/drivers/staging/comedi/Kconfig
>>> +++ b/drivers/staging/comedi/Kconfig
>>> @@ -2,6 +2,7 @@ config COMEDI
>>> 	tristate "Data acquisition support (comedi)"
>>> 	default N
>>> 	depends on m
>>> +	depends on BROKEN || FRV || M32R || MN10300 || SUPERH || TILE || X86
>> 
>> I'm sure I got comedi to compile on a 32-bit PPC board not that long ago. Has
>> something changed, or is this just not an exhaustive list?
> 
> (Adding the PPC folks to cc.)
> 
> A "git grep -w PAGE_KERNEL_NOCACHE arch/powerpc/" doesn't find anything so
> I don't think the driver will build there.  I don't have a PPC toolchain
> to verify that.

I can verify it fails on PPC as well:

drivers/staging/comedi/drivers.c: In function 'comedi_buf_alloc':
drivers/staging/comedi/drivers.c:505:37: error: 'PAGE_KERNEL_NOCACHE' undeclared (first use in this function)
drivers/staging/comedi/drivers.c:505:37: note: each undeclared identifier is reported only once for each function it appears in

However, we do have a #define for PAGE_KERNEL_NC.

- k--
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