linux-kernel - Re: [PATCH] UIO: Allow a UIO driver to override the default pgprot when we mmap

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Message-Id: <AEAF26D0-640A-4DD2-82FE-B3BD02662EEC@kernel.crashing.org>
Date:	Wed, 12 Oct 2011 11:08:20 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	"Hans J. Koch" <hjk@...sjkoch.de>
Cc:	gregkh@...e.de, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UIO: Allow a UIO driver to override the default pgprot when we mmap


On Oct 12, 2011, at 10:35 AM, Hans J. Koch wrote:

> On Wed, Oct 12, 2011 at 09:43:36AM -0500, Kumar Gala wrote:
>> For some devices the default behavior of pgprot_noncached is not
>> the correct flags for the address space.
> 
> For what devices? Can you give a real world usecase where this is needed?
> 
> Thanks,
> Hans

In the Freescale Networking devices we have a coherent memory interface to our HW queuing system.  In that case we want to change the pgprot() to be cache-able instead of non-cached.

- k

> 
>> Provide a means for the
>> kernel side UIO driver to override the flags without having to
>> implement its own full mmap callback.
>> 
>> Signed-off-by: Kumar Gala <galak@...nel.crashing.org>
>> ---
>> drivers/uio/uio.c          |    6 +++++-
>> include/linux/uio_driver.h |    2 ++
>> 2 files changed, 7 insertions(+), 1 deletions(-)
>> 
>> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
>> index d2efe82..88f4444 100644
>> --- a/drivers/uio/uio.c
>> +++ b/drivers/uio/uio.c
>> @@ -656,7 +656,11 @@ static int uio_mmap_physical(struct vm_area_struct *vma)
>> 
>> 	vma->vm_flags |= VM_IO | VM_RESERVED;
>> 
>> -	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> +	if (idev->info->mem[mi].set_pgprot)
>> +		vma->vm_page_prot =
>> +			idev->info->mem[mi].set_pgprot(vma->vm_page_prot);
>> +	else
>> +		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> 
>> 	return remap_pfn_range(vma,
>> 			       vma->vm_start,
>> diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
>> index 665517c..4c618cd 100644
>> --- a/include/linux/uio_driver.h
>> +++ b/include/linux/uio_driver.h
>> @@ -28,6 +28,7 @@ struct uio_map;
>>  * @memtype:		type of memory addr points to
>>  * @internal_addr:	ioremap-ped version of addr, for driver internal use
>>  * @map:		for use by the UIO core only.
>> + * @set_pgprot:		allow driver to override default(noncached) pgprot
>>  */
>> struct uio_mem {
>> 	const char		*name;
>> @@ -36,6 +37,7 @@ struct uio_mem {
>> 	int			memtype;
>> 	void __iomem		*internal_addr;
>> 	struct uio_map		*map;
>> +	pgprot_t (*set_pgprot)(pgprot_t prot);
>> };
>> 
>> #define MAX_UIO_MAPS	5
>> -- 
>> 1.7.3.4
>> 
>> 

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