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

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Message-ID: <4E032DF2.20108@ge.com>
Date:	Thu, 23 Jun 2011 13:13:38 +0100
From:	Martyn Welch <martyn.welch@...com>
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,
	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 23/06/11 13:02, 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.

Ah, just found the tree looks like I had a little patch to make it seemingly
work, though it will make it "not work" for most other archs at a guess (it
may not even be right on PPC):

diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c
index 44d6b62..263ad3d 100644
--- a/drivers/staging/comedi/drivers.c
+++ b/drivers/staging/comedi/drivers.c
@@ -505,7 +505,7 @@ int comedi_buf_alloc(struct comedi_device *dev, struct
comedi_subdevice *s,
                }
                if (i == n_pages) {
                        async->prealloc_buf =
-                           vmap(pages, n_pages, VM_MAP, PAGE_KERNEL_NOCACHE);
+                           vmap(pages, n_pages, VM_MAP, PAGE_KERNEL_NC);
                }
                vfree(pages);

(Sorry for the wrapping)

-- 
Martyn Welch (Principal Software Engineer) | Registered in England and
GE Intelligent Platforms                   | Wales (3828642) at 100
T +44(0)127322748                          | Barbirolli Square, Manchester,
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