On 5 November 2014 20:39, Kumar Gala <[email protected]> wrote:
>
> On Nov 5, 2014, at 6:55 AM, Ankit Jindal <[email protected]> wrote:
>
>> Hi Kumar,
>>
>> On 31 October 2014 19:09, Kumar Gala <[email protected]> wrote:
>>>
>>> On Oct 31, 2014, at 4:30 AM, Ankit Jindal <[email protected]> wrote:
>>>
>>>> Hi Kumar,
>>>>
>>>> On 21 October 2014 12:08, Kumar Gala <[email protected]> wrote:
>>>>>
>>>>> On Oct 21, 2014, at 7:56 AM, Ankit Jindal <[email protected]> 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 <[email protected]>
>>>>>> Signed-off-by: Tushar Jagad <[email protected]>
>>>>>> ---
>>>>>> 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/
>>
>> The suggested solution looks okey but not sure whether there is any
>> available drivers using different combinations. Also, I looked at the
>> available pgprot routines, looks like only pgprot_noncached and
>> pgprot_writecombine are the available ones. So if we are not going to
>> use these pgprot routines then driver might have architecture
>> dependent switches, which we should avoid.
>
> There are cases that are arch/driver specific that do not fall into
> pgprot_noncached or pgprot_writecombine. So I don’t see why we should limit
> them. For example the Freescale networking guys need cacheable-noncoherent
> for some of their UIO work.
>
> We can deal with arch specific issues during review of the UIO driver
> themselves.
Ok. But, in our case we do not want to set any special attribute,
instead just want to avoid setting non-cacheable attribute. So if we
go by the approach as in your patch, then I need to register a dummy
routine which does nothing.
I think another approach could be to have new mem type as in this
patch and add something like this to this patch:
if (cacheable) {
/* check if driver want to set any special cacheable attribute
combination */
if (idev->info->set_pgprot)
idev->info->set_pgprot(vma->vm_page_prot)
} else {
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
}
Please let me know your view.
> - k
>
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
Thanks,
Ankit
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