Memory sharing issue by application on V4L2 based device driver with

Memory sharing issue by application on V4L2 based device driver with

[daeinki]

Hello, all.

I'd like to discuss memory sharing issue by application on v4l2 based
device driver with system mmu and get some advices about that.

Now I am working on Samsung SoC C210 platform and this platform has some
multimedia devices with system mmu such as fimc, and mfc also we have
implemented device drivers for them. those drivers are based on V4L2
framework with videobuf2. for system mmu of each device, we used
VCM(Virtual Contiguous Memory) framework.

Simply, VCM framework provides  physical memory, device virtual memory
allocation and memory mapping between them. when device driver is
initialized or operated by user application, each driver allocates
physical memory and device virtual memory and then mapping using VCM
interface.

refer to below link for more detail.
http://www.spinics.net/lists/linux-media/msg26548.html

Physical memory access process is as the following.
            DVA                          PA
device --------------> system mmu ------------------> physical memory

DVA : device virtual address.
PA : physical address.

like this, device virtual address should be set to buffer(source or
destination) register of multimedia device.

the problem is that application want to share own memory with any device
driver to avoid memory copy. in other words, user-allocated memory could
be source or destination memory of multimedia device driver.


let's see the diagram below.

                user application

                      |
                      |
                      |
                      |
                      |  1. UVA(allocated by malloc)
                      |
                      |
                    ¡¬|/                   2. UVA(in page unit)

        -----> multimedia device driver -------------------> videobuf2
        |
        |        |     ^                                         |
        |        |     |                                         |
        |        |     -------------------------------------------
        |        |                    3. PA(in page unit)
        |        |
        |        | 4. PA(in page unit)
6. DVA  |        |
        |        |
        |        |
        |      ¡¬|/
        |
        |       Virtual Contiguous Memory ---------
        |                                         |
        |           |     ^                       |
        |           |     |                       | 5. map PA to DVA
        |           |     |                       |
        |           |     |                       |
        -------------     -------------------------

PA : physical address.
UVA : user virtual address.
DVA : device virtual address.

1. user application allocates user space memory through malloc function
and sending it to multimedia device driver based on v4l2 framework
through userptr feature.

2, 3. multimedia device driver gets translated physical address from
videobuf2 framework in page unit.

4, 5. multimedia device driver gets allocated device virtual address and
mapping it to physical address and then mapping them through VCM interface.

6. multimedia device driver sets device virtual address from VCM to
buffer register.

the diagram above is fully theoretical so I wonder that this way is
reasonable and has some problems also what should be considered.

thank you for your interesting.

Re: Memory sharing issue by application on V4L2 based device driver

[InKi Dae]

thank you for your comments.

your second comment has no any problem as I said before, user virtual
addess could be translated in page unit. but the problem, as you said,
is that when cpu access to the memory in user mode, the memory
allocated by malloc, page fault occurs so we can't find pfn to user
virtual address. I missed that. but I think we could resolve this one.

as before, user application allocates memory through malloc function
and then send it to device driver(using userptr feature). if the pfn
is null when device driver translated user virtual address in page
unit then it allocates phsical memory in page unit using some
interface such as alloc_page() and then mapping them. when pfn is
null, to check it and allocate physical memory in page unit could be
processed by videobuf2.

of course, videobuf2 has no any duty considered for system mmu. so
videobuf2 just provides callback for 3rd party and any platform with
system mmu such as Samsung SoC C210 implements the function(allocating
physical memory and mapping it) and registers it to callback of
videobuf2. by doing so, I think your first comment could be cleared.

please, feel free to give me your opinion and pointing out.

thank you.

2011년 1월 7일 오전 8:57, Jonghun Han <jonghun.han@samsung.com>님의 말:
>
> Hello,
>
> There are two reasons why malloc isn't suitable for it.
>
> The first is that malloc doesn't allocate memory when malloc is called.
> So driver or vb2 cannot find PFN for it in the VIDIOC_QBUF.
>
> The second is that malloc uses 4KB page allocation.
> SYS.MMU(IO-MMU) can handle scattered memory. But it has a penalty when TLB
> miss is occurred.
> So as possible as physically contiguous pages are needed for performance
> enhancement.
>
> So new allocator which can clear two main issues is needed.
>
> Best regards,
>
>> -----Original Message-----
>> From: linux-media-owner@vger.kernel.org [mailto:linux-media-
>> owner@vger.kernel.org] On Behalf Of InKi Dae
>> Sent: Thursday, January 06, 2011 10:25 PM
>> To: linux-media@vger.kernel.org
>> Subject: Memory sharing issue by application on V4L2 based device driver
> with
>> system mmu.
>>
>> Hello, all.
>>
>> I'd like to discuss memory sharing issue by application on v4l2 based
> device driver
>> with system mmu and get some advices about that.
>>
>> Now I am working on Samsung SoC C210 platform and this platform has some
>> multimedia devices with system mmu such as fimc, and mfc also we have
>> implemented device drivers for them. those drivers are based on V4L2
> framework
>> with videobuf2. for system mmu of each device, we used VCM(Virtual
> Contiguous
>> Memory) framework.
>>
>> Simply, VCM framework provides  physical memory, device virtual memory
>> allocation and memory mapping between them. when device driver is
> initialized or
>> operated by user application, each driver allocates physical memory and
> device
>> virtual memory and then mapping using VCM interface.
>>
>> refer to below link for more detail.
>> http://www.spinics.net/lists/linux-media/msg26548.html
>>
>> Physical memory access process is as the following.
>>            DVA                          PA
>> device --------------> system mmu ------------------> physical memory
>>
>> DVA : device virtual address.
>> PA : physical address.
>>
>> like this, device virtual address should be set to buffer(source or
>> destination) register of multimedia device.
>>
>> the problem is that application want to share own memory with any device
> driver to
>> avoid memory copy. in other words, user-allocated memory could be source
> or
>> destination memory of multimedia device driver.
>>
>>
>> let's see the diagram below.
>>
>>                user application
>>
>>                      |
>>                      |
>>                      |
>>                      |
>>                      |  1. UVA(allocated by malloc)
>>                      |
>>                      |
>>                    ＼|/                   2. UVA(in page unit)
>>
>>        -----> multimedia device driver -------------------> videobuf2
>>        |
>>        |        |     ^                                         |
>>        |        |     |                                         |
>>        |        |     -------------------------------------------
>>        |        |                    3. PA(in page unit)
>>        |        |
>>        |        | 4. PA(in page unit)
>> 6. DVA  |        |
>>        |        |
>>        |        |
>>        |      ＼|/
>>        |
>>        |       Virtual Contiguous Memory ---------
>>        |                                         |
>>        |           |     ^                       |
>>        |           |     |                       | 5. map PA to DVA
>>        |           |     |                       |
>>        |           |     |                       |
>>        -------------     -------------------------
>>
>> PA : physical address.
>> UVA : user virtual address.
>> DVA : device virtual address.
>>
>> 1. user application allocates user space memory through malloc function
> and
>> sending it to multimedia device driver based on v4l2 framework through
> userptr
>> feature.
>>
>> 2, 3. multimedia device driver gets translated physical address from
>> videobuf2 framework in page unit.
>>
>> 4, 5. multimedia device driver gets allocated device virtual address and
> mapping it
>> to physical address and then mapping them through VCM interface.
>>
>> 6. multimedia device driver sets device virtual address from VCM to
> buffer register.
>>
>> the diagram above is fully theoretical so I wonder that this way is
> reasonable and
>> has some problems also what should be considered.
>>
>> thank you for your interesting.
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body
>> of a message to majordomo@vger.kernel.org More majordomo info at
>> http://vger.kernel.org/majordomo-info.html
>
>
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RE: Memory sharing issue by application on V4L2 based device driver

[Jonghun Han]

Hello,

That's not a translation issue. What I mention is the size of allocation.
The malloc uses 4KB page allocation and SYS.MMU can handle it.
But 64KB or 1MB physically contiguous memory is better than 4KB page in the
point of performance.

Best regards,

> -----Original Message-----
> From: linux-media-owner@vger.kernel.org [mailto:linux-media-
> owner@vger.kernel.org] On Behalf Of InKi Dae
> Sent: Friday, January 07, 2011 11:17 AM
> To: Jonghun Han
> Cc: linux-media@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
linux-fbdev;
> kyungmin.park@samsung.com
> Subject: Re: Memory sharing issue by application on V4L2 based device
driver
> with system mmu.
> 
> thank you for your comments.
> 
> your second comment has no any problem as I said before, user virtual
addess
> could be translated in page unit. but the problem, as you said, is that
when cpu
> access to the memory in user mode, the memory allocated by malloc, page
fault
> occurs so we can't find pfn to user virtual address. I missed that. but I
think we
> could resolve this one.
> 
> as before, user application allocates memory through malloc function and
then
> send it to device driver(using userptr feature). if the pfn is null when
device driver
> translated user virtual address in page unit then it allocates phsical
memory in
> page unit using some interface such as alloc_page() and then mapping
them. when
> pfn is null, to check it and allocate physical memory in page unit could
be
> processed by videobuf2.
> 
> of course, videobuf2 has no any duty considered for system mmu. so
> videobuf2 just provides callback for 3rd party and any platform with
system mmu
> such as Samsung SoC C210 implements the function(allocating physical
memory
> and mapping it) and registers it to callback of videobuf2. by doing so, I
think your
> first comment could be cleared.
> 
> please, feel free to give me your opinion and pointing out.
> 
> thank you.
> 
> 2011년 1월 7일 오전 8:57, Jonghun Han <jonghun.han@samsung.com>님의 말:
> >
> > Hello,
> >
> > There are two reasons why malloc isn't suitable for it.
> >
> > The first is that malloc doesn't allocate memory when malloc is called.
> > So driver or vb2 cannot find PFN for it in the VIDIOC_QBUF.
> >
> > The second is that malloc uses 4KB page allocation.
> > SYS.MMU(IO-MMU) can handle scattered memory. But it has a penalty when
> > TLB miss is occurred.
> > So as possible as physically contiguous pages are needed for
> > performance enhancement.
> >
> > So new allocator which can clear two main issues is needed.
> >
> > Best regards,
> >
> >> -----Original Message-----
> >> From: linux-media-owner@vger.kernel.org [mailto:linux-media-
> >> owner@vger.kernel.org] On Behalf Of InKi Dae
> >> Sent: Thursday, January 06, 2011 10:25 PM
> >> To: linux-media@vger.kernel.org
> >> Subject: Memory sharing issue by application on V4L2 based device
> >> driver
> > with
> >> system mmu.
> >>
> >> Hello, all.
> >>
> >> I'd like to discuss memory sharing issue by application on v4l2 based
> > device driver
> >> with system mmu and get some advices about that.
> >>
> >> Now I am working on Samsung SoC C210 platform and this platform has
> >> some multimedia devices with system mmu such as fimc, and mfc also we
> >> have implemented device drivers for them. those drivers are based on
> >> V4L2
> > framework
> >> with videobuf2. for system mmu of each device, we used VCM(Virtual
> > Contiguous
> >> Memory) framework.
> >>
> >> Simply, VCM framework provides  physical memory, device virtual
> >> memory allocation and memory mapping between them. when device driver
> >> is
> > initialized or
> >> operated by user application, each driver allocates physical memory
> >> and
> > device
> >> virtual memory and then mapping using VCM interface.
> >>
> >> refer to below link for more detail.
> >> http://www.spinics.net/lists/linux-media/msg26548.html
> >>
> >> Physical memory access process is as the following.
> >>            DVA                          PA
> >> device --------------> system mmu ------------------> physical memory
> >>
> >> DVA : device virtual address.
> >> PA : physical address.
> >>
> >> like this, device virtual address should be set to buffer(source or
> >> destination) register of multimedia device.
> >>
> >> the problem is that application want to share own memory with any
> >> device
> > driver to
> >> avoid memory copy. in other words, user-allocated memory could be
> >> source
> > or
> >> destination memory of multimedia device driver.
> >>
> >>
> >> let's see the diagram below.
> >>
> >>                user application
> >>
> >>                      |
> >>                      |
> >>                      |
> >>                      |
> >>                      |  1. UVA(allocated by malloc)
> >>                      |
> >>                      |
> >>                    ＼|/                   2. UVA(in page unit)
> >>
> >>        -----> multimedia device driver -------------------> videobuf2
> >>        |
> >>        |        |     ^                                         |
> >>        |        |     |                                         |
> >>        |        |     -------------------------------------------
> >>        |        |                    3. PA(in page unit)
> >>        |        |
> >>        |        | 4. PA(in page unit)
> >> 6. DVA  |        |
> >>        |        |
> >>        |        |
> >>        |      ＼|/
> >>        |
> >>        |       Virtual Contiguous Memory ---------
> >>        |                                         |
> >>        |           |     ^                       |
> >>        |           |     |                       | 5. map PA to DVA
> >>        |           |     |                       |
> >>        |           |     |                       |
> >>        -------------     -------------------------
> >>
> >> PA : physical address.
> >> UVA : user virtual address.
> >> DVA : device virtual address.
> >>
> >> 1. user application allocates user space memory through malloc
> >> function
> > and
> >> sending it to multimedia device driver based on v4l2 framework
> >> through
> > userptr
> >> feature.
> >>
> >> 2, 3. multimedia device driver gets translated physical address from
> >> videobuf2 framework in page unit.
> >>
> >> 4, 5. multimedia device driver gets allocated device virtual address
> >> and
> > mapping it
> >> to physical address and then mapping them through VCM interface.
> >>
> >> 6. multimedia device driver sets device virtual address from VCM to
> > buffer register.
> >>
> >> the diagram above is fully theoretical so I wonder that this way is
> > reasonable and
> >> has some problems also what should be considered.
> >>
> >> thank you for your interesting.
> >>
> >> _______________________________________________
> >> linux-arm-kernel mailing list
> >> linux-arm-kernel@lists.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe
> >> linux-media" in
> > the body
> >> of a message to majordomo@vger.kernel.org More majordomo info at
> >> http://vger.kernel.org/majordomo-info.html
> >
> >
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body
> of a message to majordomo@vger.kernel.org More majordomo info at
> http://vger.kernel.org/majordomo-info.html

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Re: Memory sharing issue by application on V4L2 based device driver

[daeinki]

Hello, Mr. Jonghun.

please, note that user process's pgd and device's pgd with system mmu
are differnent. first, the memory allocated by user malloc should be
mapped to physical memory in page unit because user app also should be
accessed to own memory region. and when mapping the physical memory to
device virtual address, it creates page table entry for 64k or 1M and
then could map physical address to those entries. therefore what you
mention has no problem.

actual issue is not to need demend paging, some issues we don't
understand may exist as side effects.

thank you.

Jonghun Han 쓴 글:
> Hello,
> 
> That's not a translation issue. What I mention is the size of allocation.
> The malloc uses 4KB page allocation and SYS.MMU can handle it.
> But 64KB or 1MB physically contiguous memory is better than 4KB page in the
> point of performance.
> 
> Best regards,
> 
>> -----Original Message-----
>> From: linux-media-owner@vger.kernel.org [mailto:linux-media-
>> owner@vger.kernel.org] On Behalf Of InKi Dae
>> Sent: Friday, January 07, 2011 11:17 AM
>> To: Jonghun Han
>> Cc: linux-media@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> linux-fbdev;
>> kyungmin.park@samsung.com
>> Subject: Re: Memory sharing issue by application on V4L2 based device
> driver
>> with system mmu.
>>
>> thank you for your comments.
>>
>> your second comment has no any problem as I said before, user virtual
> addess
>> could be translated in page unit. but the problem, as you said, is that
> when cpu
>> access to the memory in user mode, the memory allocated by malloc, page
> fault
>> occurs so we can't find pfn to user virtual address. I missed that. but I
> think we
>> could resolve this one.
>>
>> as before, user application allocates memory through malloc function and
> then
>> send it to device driver(using userptr feature). if the pfn is null when
> device driver
>> translated user virtual address in page unit then it allocates phsical
> memory in
>> page unit using some interface such as alloc_page() and then mapping
> them. when
>> pfn is null, to check it and allocate physical memory in page unit could
> be
>> processed by videobuf2.
>>
>> of course, videobuf2 has no any duty considered for system mmu. so
>> videobuf2 just provides callback for 3rd party and any platform with
> system mmu
>> such as Samsung SoC C210 implements the function(allocating physical
> memory
>> and mapping it) and registers it to callback of videobuf2. by doing so, I
> think your
>> first comment could be cleared.
>>
>> please, feel free to give me your opinion and pointing out.
>>
>> thank you.
>>
>> 2011년 1월 7일 오전 8:57, Jonghun Han <jonghun.han@samsung.com>님의 말:
>>> Hello,
>>>
>>> There are two reasons why malloc isn't suitable for it.
>>>
>>> The first is that malloc doesn't allocate memory when malloc is called.
>>> So driver or vb2 cannot find PFN for it in the VIDIOC_QBUF.
>>>
>>> The second is that malloc uses 4KB page allocation.
>>> SYS.MMU(IO-MMU) can handle scattered memory. But it has a penalty when
>>> TLB miss is occurred.
>>> So as possible as physically contiguous pages are needed for
>>> performance enhancement.
>>>
>>> So new allocator which can clear two main issues is needed.
>>>
>>> Best regards,
>>>
>>>> -----Original Message-----
>>>> From: linux-media-owner@vger.kernel.org [mailto:linux-media-
>>>> owner@vger.kernel.org] On Behalf Of InKi Dae
>>>> Sent: Thursday, January 06, 2011 10:25 PM
>>>> To: linux-media@vger.kernel.org
>>>> Subject: Memory sharing issue by application on V4L2 based device
>>>> driver
>>> with
>>>> system mmu.
>>>>
>>>> Hello, all.
>>>>
>>>> I'd like to discuss memory sharing issue by application on v4l2 based
>>> device driver
>>>> with system mmu and get some advices about that.
>>>>
>>>> Now I am working on Samsung SoC C210 platform and this platform has
>>>> some multimedia devices with system mmu such as fimc, and mfc also we
>>>> have implemented device drivers for them. those drivers are based on
>>>> V4L2
>>> framework
>>>> with videobuf2. for system mmu of each device, we used VCM(Virtual
>>> Contiguous
>>>> Memory) framework.
>>>>
>>>> Simply, VCM framework provides  physical memory, device virtual
>>>> memory allocation and memory mapping between them. when device driver
>>>> is
>>> initialized or
>>>> operated by user application, each driver allocates physical memory
>>>> and
>>> device
>>>> virtual memory and then mapping using VCM interface.
>>>>
>>>> refer to below link for more detail.
>>>> http://www.spinics.net/lists/linux-media/msg26548.html
>>>>
>>>> Physical memory access process is as the following.
>>>>            DVA                          PA
>>>> device --------------> system mmu ------------------> physical memory
>>>>
>>>> DVA : device virtual address.
>>>> PA : physical address.
>>>>
>>>> like this, device virtual address should be set to buffer(source or
>>>> destination) register of multimedia device.
>>>>
>>>> the problem is that application want to share own memory with any
>>>> device
>>> driver to
>>>> avoid memory copy. in other words, user-allocated memory could be
>>>> source
>>> or
>>>> destination memory of multimedia device driver.
>>>>
>>>>
>>>> let's see the diagram below.
>>>>
>>>>                user application
>>>>
>>>>                      |
>>>>                      |
>>>>                      |
>>>>                      |
>>>>                      |  1. UVA(allocated by malloc)
>>>>                      |
>>>>                      |
>>>>                    ＼|/                   2. UVA(in page unit)
>>>>
>>>>        -----> multimedia device driver -------------------> videobuf2
>>>>        |
>>>>        |        |     ^                                         |
>>>>        |        |     |                                         |
>>>>        |        |     -------------------------------------------
>>>>        |        |                    3. PA(in page unit)
>>>>        |        |
>>>>        |        | 4. PA(in page unit)
>>>> 6. DVA  |        |
>>>>        |        |
>>>>        |        |
>>>>        |      ＼|/
>>>>        |
>>>>        |       Virtual Contiguous Memory ---------
>>>>        |                                         |
>>>>        |           |     ^                       |
>>>>        |           |     |                       | 5. map PA to DVA
>>>>        |           |     |                       |
>>>>        |           |     |                       |
>>>>        -------------     -------------------------
>>>>
>>>> PA : physical address.
>>>> UVA : user virtual address.
>>>> DVA : device virtual address.
>>>>
>>>> 1. user application allocates user space memory through malloc
>>>> function
>>> and
>>>> sending it to multimedia device driver based on v4l2 framework
>>>> through
>>> userptr
>>>> feature.
>>>>
>>>> 2, 3. multimedia device driver gets translated physical address from
>>>> videobuf2 framework in page unit.
>>>>
>>>> 4, 5. multimedia device driver gets allocated device virtual address
>>>> and
>>> mapping it
>>>> to physical address and then mapping them through VCM interface.
>>>>
>>>> 6. multimedia device driver sets device virtual address from VCM to
>>> buffer register.
>>>> the diagram above is fully theoretical so I wonder that this way is
>>> reasonable and
>>>> has some problems also what should be considered.
>>>>
>>>> thank you for your interesting.
>>>>
>>>> _______________________________________________
>>>> linux-arm-kernel mailing list
>>>> linux-arm-kernel@lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-media" in
>>> the body
>>>> of a message to majordomo@vger.kernel.org More majordomo info at
>>>> http://vger.kernel.org/majordomo-info.html
>>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body
>> of a message to majordomo@vger.kernel.org More majordomo info at
>> http://vger.kernel.org/majordomo-info.html
> 
> --
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Re: Memory sharing issue by application on V4L2 based device

[Konrad Rzeszutek Wilk]

 .. snip..
> But 64KB or 1MB physically contiguous memory is better than 4KB page in the
> point of performance.

Could you explain that in more details please? I presume you are
talking about a CPU that has a MMU unit, right?

RE: Memory sharing issue by application on V4L2 based device driver

[Jonghun Han]

Sorry for late reply.

Samsung SoC C210 has many multimedia IPs.
Each IP has its own MMU named SYSTEM MMU like CPU's MMU.
So it can handle discontiguous memory using device own virtual address.

What Inki Dae wants to discuss is how to allocate the memory and how to
share it with other multimedia IPs. 

Thank you for interesting.

Best regards,

> -----Original Message-----
> From: linux-fbdev-owner@vger.kernel.org [mailto:linux-fbdev-
> owner@vger.kernel.org] On Behalf Of Konrad Rzeszutek Wilk
> Sent: Wednesday, January 12, 2011 2:35 AM
> To: Jonghun Han
> Cc: 'InKi Dae'; linux-media@vger.kernel.org;
linux-arm-kernel@lists.infradead.org;
> 'linux-fbdev'; kyungmin.park@samsung.com
> Subject: Re: Memory sharing issue by application on V4L2 based device
driver
> with system mmu.
> 
> 
>  .. snip..
> > But 64KB or 1MB physically contiguous memory is better than 4KB page
> > in the point of performance.
> 
> Could you explain that in more details please? I presume you are talking
about a
> CPU that has a MMU unit, right?
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in
the body
> of a message to majordomo@vger.kernel.org More majordomo info at
> http://vger.kernel.org/majordomo-info.html

Re: Memory sharing issue by application on V4L2 based device

[Michel Dänzer]

On Fre, 2011-01-07 at 11:17 +0900, InKi Dae wrote: 
> thank you for your comments.
> 
> your second comment has no any problem as I said before, user virtual
> addess could be translated in page unit. but the problem, as you said,
> is that when cpu access to the memory in user mode, the memory
> allocated by malloc, page fault occurs so we can't find pfn to user
> virtual address. I missed that. but I think we could resolve this one.
> 
> as before, user application allocates memory through malloc function
> and then send it to device driver(using userptr feature). if the pfn
> is null when device driver translated user virtual address in page
> unit then it allocates phsical memory in page unit using some
> interface such as alloc_page() and then mapping them. when pfn is
> null, to check it and allocate physical memory in page unit could be
> processed by videobuf2.
> 
> of course, videobuf2 has no any duty considered for system mmu. so
> videobuf2 just provides callback for 3rd party and any platform with
> system mmu such as Samsung SoC C210 implements the function(allocating
> physical memory and mapping it) and registers it to callback of
> videobuf2. by doing so, I think your first comment could be cleared.

FWIW, TTM (drivers/gpu/drm/ttm, include/drm/ttm) is designed and used
for managing memory between CPU/GPU and kernel/userspace access. I
haven't looked at your requirements in detail, but if you haven't looked
at TTM yet, it sounds like it might be worth a look.


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer

Re: Memory sharing issue by application on V4L2 based device driver

[daeinki]

Michel Dänzer 쓴 글:
> On Fre, 2011-01-07 at 11:17 +0900, InKi Dae wrote: 
>> thank you for your comments.
>>
>> your second comment has no any problem as I said before, user virtual
>> addess could be translated in page unit. but the problem, as you said,
>> is that when cpu access to the memory in user mode, the memory
>> allocated by malloc, page fault occurs so we can't find pfn to user
>> virtual address. I missed that. but I think we could resolve this one.
>>
>> as before, user application allocates memory through malloc function
>> and then send it to device driver(using userptr feature). if the pfn
>> is null when device driver translated user virtual address in page
>> unit then it allocates phsical memory in page unit using some
>> interface such as alloc_page() and then mapping them. when pfn is
>> null, to check it and allocate physical memory in page unit could be
>> processed by videobuf2.
>>
>> of course, videobuf2 has no any duty considered for system mmu. so
>> videobuf2 just provides callback for 3rd party and any platform with
>> system mmu such as Samsung SoC C210 implements the function(allocating
>> physical memory and mapping it) and registers it to callback of
>> videobuf2. by doing so, I think your first comment could be cleared.
> 
> FWIW, TTM (drivers/gpu/drm/ttm, include/drm/ttm) is designed and used
> for managing memory between CPU/GPU and kernel/userspace access. I
> haven't looked at your requirements in detail, but if you haven't looked
> at TTM yet, it sounds like it might be worth a look.
> 
> 
Thank you for your advice. I would look at TTM driver.