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

Kumar Gala
2011-10-12T16:08:31Z

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@kernel.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
>>
>>