On Oct 31, 2014, at 4:30 AM, Ankit Jindal <ankit.jin...@linaro.org> wrote:
> Hi Kumar,
>
> On 21 October 2014 12:08, Kumar Gala <ga...@codeaurora.org> wrote:
>>
>> On Oct 21, 2014, at 7:56 AM, Ankit Jindal <ankit.jin...@linaro.org> wrote:
>>
>>> Currently, three types of mem regions are supported: UIO_MEM_PHYS,
>>> UIO_MEM_LOGICAL and UIO_MEM_VIRTUAL. Among these UIO_MEM_PHYS helps
>>> UIO driver export physcial memory to user space as non-cacheable
>>> user memory. Typcially memory-mapped registers of a device are exported
>>> to user space as UIO_MEM_PHYS type mem region. The UIO_MEM_PHYS type
>>> is not efficient if dma-capable devices are capable of maintaining coherency
>>> with CPU caches.
>>>
>>> This patch adds new type UIO_MEM_PHYS_CACHE for mem regions to enable
>>> cacheable access to physical memory from user space.
>>>
>>> Signed-off-by: Ankit Jindal <ankit.jin...@linaro.org>
>>> Signed-off-by: Tushar Jagad <tushar.ja...@linaro.org>
>>> ---
>>> drivers/uio/uio.c | 11 ++++++++---
>>> include/linux/uio_driver.h | 1 +
>>> 2 files changed, 9 insertions(+), 3 deletions(-)
>>
>> Rather than adding a new type, why not allow the driver to set the pgprot
>> value, this way one has full control and we don’t need to keep adding types
>> for various different cache attributions in the future.
>
> Do you mean to add a new field pgprot_t in the memtype structure and
> uio_mmap_physical will set vma->vm_page_prot to this value provided by
> driver ? If this is the case then we will need to change all the
> current uio based drivers which was the reason I preferred to have a
> new mem type.
>
> Please let me know if I have misunderstood anything.
I’m suggeting in uio_mmap_physical to do something like:
if (idev->info->set_pgprot)
idev->info->set_pgprot(vma->vm_page_prot)
else
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
And add a set_prprot callback to 'struct uio_info’.
Here’s patch from several years ago:
http://patchwork.ozlabs.org/patch/119224/
- k
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