Re: [Xen-devel] swiotlb-xen question

[Oleksandr Dmytryshyn <oleksandr.dmytryshyn@xxxxxxxxxxxxxxx>]

On Wed, Mar 26, 2014 at 4:46 PM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Wed, Mar 26, 2014 at 12:35:12PM +0200, Oleksandr Dmytryshyn wrote:
>> Hi to all.
>>
>> Currently I'm using hypervisor on ARM Cortex A15 processor (DRA7xx
>> Jacinto 6 processor). I'm using mainline xen 4.4 with some patches on
>> top plus dom0 and domU linux kernel 3.8.
>>
>> I've written a hack to make a camera working on my board in dom0
>> (drivers for camera and display system are in dom0). An user-space
>> application in dom0 is used to test camera (it reads camera captured
>> data and sends it to the framebuffer). In the kernel code I've implemented
>> .mmap callback function in the swiotlb-xen.c file (like xen_swiotlb_mmap())
>> and copied to this new callback all content from the original function
>> 'arm_dma_mmap()' from the kernel. This function creates userspace
>> mapping for the DMA-coherent memory. With this hack camera is working
>> (I can see captured video on display).
>
> Why can't you use the v4l API? Won't that work?
>
Currently we are using v4l api. swiotlb-xen doesnt have mmap callback
implemented,
so kernel use standard function dma_common_mmap() to map memory. But this
function doesn't work correctly. We've also tried to use arm_dma_mmap() function
instead of the dma_common_mmap() (HACK in the file
include/asm-generic/dma-mapping-common.h only for dom0) and all is working
in this case.
>>
>> For now I have little understanding how swiotlb-xen is working. Currently in 
>> the
>> mainline linux kernel this callback is not implemented.
>>
>> Here is my question.
>> Does anyone know are there any plans to implement
>> this callback for swiotlb-xen (in linux kernel) in the right way?
>>
>> Oleksandr Dmytryshyn | Product Engineering and Development
>> GlobalLogic
>> P x3657  M +38.067.382.2525
>> www.globallogic.com
>>
>> http://www.globallogic.com/email_disclaimer.txt
>>
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