DMA over USB

DMA over USB

[Raghavendra]

Hello,

I have a query regarding DMA(Direct Memory Access) for the usb devices.

The understanding of DMA actions over PCI is straight forward. PCI 
devices support bus mastering capability, such that the PCI devices 
could take the ownership of the bus and perform access to the memory 
directly, and a software support exists for the same in Linux.

As far as USB devices are concerned, they don?t have the bus mastering 
capability like the PCI devices.
But the USB URB structure have a field named 'dma_addr_t transfer_dma', 
used for DMA access. The USB driver allocate the DMA buffers coherently 
and pass the DMA address to the URBs during its initialization.
As far as Linux is concerned, how the DMA action being taking place for 
USB devices. As per my understanding, the USB host controller is taking 
care of the DMA operations. But I require a little more insight into it.

Further more, if it is possible for the USB devices, then can this 
support be also extended towards low-end protocols such as I2C or SPI?

Thanks,
Raghavendra

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DMA over USB

[Mandeep Sandhu]

You might want to ask this question to the USB experts on the
linux-usb ML - linux-usb at vger.kernel.org

HTH,
-mandeep

On Tue, Jul 1, 2014 at 10:10 PM, Raghavendra <arrao@cdac.in> wrote:
> Hello,
>
> I have a query regarding DMA(Direct Memory Access) for the usb devices.
>
> The understanding of DMA actions over PCI is straight forward. PCI
> devices support bus mastering capability, such that the PCI devices
> could take the ownership of the bus and perform access to the memory
> directly, and a software support exists for the same in Linux.
>
> As far as USB devices are concerned, they don?t have the bus mastering
> capability like the PCI devices.
> But the USB URB structure have a field named 'dma_addr_t transfer_dma',
> used for DMA access. The USB driver allocate the DMA buffers coherently
> and pass the DMA address to the URBs during its initialization.
> As far as Linux is concerned, how the DMA action being taking place for
> USB devices. As per my understanding, the USB host controller is taking
> care of the DMA operations. But I require a little more insight into it.
>
> Further more, if it is possible for the USB devices, then can this
> support be also extended towards low-end protocols such as I2C or SPI?
>
> Thanks,
> Raghavendra
>
> -------------------------------------------------------------------------------------------------------------------------------
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DMA over USB

[Greg KH]

On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
> Hello,
> 
> I have a query regarding DMA(Direct Memory Access) for the usb devices.
> 
> The understanding of DMA actions over PCI is straight forward. PCI 
> devices support bus mastering capability, such that the PCI devices 
> could take the ownership of the bus and perform access to the memory 
> directly, and a software support exists for the same in Linux.
> 
> As far as USB devices are concerned, they don?t have the bus mastering 
> capability like the PCI devices.
> But the USB URB structure have a field named 'dma_addr_t transfer_dma', 
> used for DMA access. The USB driver allocate the DMA buffers coherently 
> and pass the DMA address to the URBs during its initialization.
> As far as Linux is concerned, how the DMA action being taking place for 
> USB devices. As per my understanding, the USB host controller is taking 
> care of the DMA operations. But I require a little more insight into it.

Why, what exactly are you concerned about?  What are you trying to do?

> Further more, if it is possible for the USB devices, then can this 
> support be also extended towards low-end protocols such as I2C or SPI?

It depends on your controller chips for those busses, if they support
DMA or not.

greg k-h

DMA over USB

[Greg KH]

On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
> On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
> > Hello,
> > 
> > I have a query regarding DMA(Direct Memory Access) for the usb devices.
> > 
> > The understanding of DMA actions over PCI is straight forward. PCI 
> > devices support bus mastering capability, such that the PCI devices 
> > could take the ownership of the bus and perform access to the memory 
> > directly, and a software support exists for the same in Linux.
> > 
> > As far as USB devices are concerned, they don?t have the bus mastering 
> > capability like the PCI devices.
> > But the USB URB structure have a field named 'dma_addr_t transfer_dma', 
> > used for DMA access. The USB driver allocate the DMA buffers coherently 
> > and pass the DMA address to the URBs during its initialization.
> > As far as Linux is concerned, how the DMA action being taking place for 
> > USB devices. As per my understanding, the USB host controller is taking 
> > care of the DMA operations. But I require a little more insight into it.
> 
> Why, what exactly are you concerned about?  What are you trying to do?

Also, you _have_ read the USB DMA documentation, right?

What about the documentation in this area is unclear?

thanks,

greg k-h

DMA over USB

[Chan Kim]

Hi Raghavendra,
In my case, we used USB host design from opencore. And the driver (I don't know where it came from. it's similar to sl811-hcd.c from cypress) writes or reads the data to /from the USB host. Not using DMA. I think if the USB host has DMA capability, tha pio read/write should be chnaged to triggering DMA.
http://lxr.free-electrons.com/source/drivers/usb/host/sl811-hcd.c  see line 234.
Chan



?? ?? : "Raghavendra" <arrao@cdac.in>
?? ?? : 2014-07-02 14:20:42 ( +09:00 )
?? ?? : kernelnewbies <Kernelnewbies@kernelnewbies.org>
?? : 
?? : DMA over USB

Hello,

I have a query regarding DMA(Direct Memory Access) for the usb devices.

The understanding of DMA actions over PCI is straight forward. PCI 
devices support bus mastering capability, such that the PCI devices 
could take the ownership of the bus and perform access to the memory 
directly, and a software support exists for the same in Linux.

As far as USB devices are concerned, they don?t have the bus mastering 
capability like the PCI devices.
But the USB URB structure have a field named 'dma_addr_t transfer_dma', 
used for DMA access. The USB driver allocate the DMA buffers coherently 
and pass the DMA address to the URBs during its initialization.
As far as Linux is concerned, how the DMA action being taking place for 
USB devices. As per my understanding, the USB host controller is taking 
care of the DMA operations. But I require a little more insight into it.

Further more, if it is possible for the USB devices, then can this 
support be also extended towards low-end protocols such as I2C or SPI?

Thanks,
Raghavendra

-------------------------------------------------------------------------------------------------------------------------------
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DMA over USB

[Raghavendra]

On Wednesday 02 July 2014 11:02 AM, Greg KH wrote:
> On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
>> On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
>>> Hello,
>>>
>>> I have a query regarding DMA(Direct Memory Access) for the usb devices.
>>>
>>> The understanding of DMA actions over PCI is straight forward. PCI
>>> devices support bus mastering capability, such that the PCI devices
>>> could take the ownership of the bus and perform access to the memory
>>> directly, and a software support exists for the same in Linux.
>>>
>>> As far as USB devices are concerned, they don?t have the bus mastering
>>> capability like the PCI devices.
>>> But the USB URB structure have a field named 'dma_addr_t transfer_dma',
>>> used for DMA access. The USB driver allocate the DMA buffers coherently
>>> and pass the DMA address to the URBs during its initialization.
>>> As far as Linux is concerned, how the DMA action being taking place for
>>> USB devices. As per my understanding, the USB host controller is taking
>>> care of the DMA operations. But I require a little more insight into it.
>> Why, what exactly are you concerned about?  What are you trying to do?
> Also, you _have_ read the USB DMA documentation, right?
>
> What about the documentation in this area is unclear?
Yes, I have read the documentation and its fine. I am mostly concerned 
about the all the heavy lifting happening in the background.
>
> thanks,
>
> greg k-h
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>


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-------------------------------------------------------------------------------------------------------------------------------

DMA over USB

[Raghavendra]

On Wednesday 02 July 2014 11:42 AM, Greg KH wrote:
> On Wed, Jul 02, 2014 at 11:32:47AM +0530, Raghavendra wrote:
>> On Wednesday 02 July 2014 11:02 AM, Greg KH wrote:
>>> On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
>>>> On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
>>>>> Hello,
>>>>>
>>>>> I have a query regarding DMA(Direct Memory Access) for the usb devices.
>>>>>
>>>>> The understanding of DMA actions over PCI is straight forward. PCI
>>>>> devices support bus mastering capability, such that the PCI devices
>>>>> could take the ownership of the bus and perform access to the memory
>>>>> directly, and a software support exists for the same in Linux.
>>>>>
>>>>> As far as USB devices are concerned, they don?t have the bus mastering
>>>>> capability like the PCI devices.
>>>>> But the USB URB structure have a field named 'dma_addr_t transfer_dma',
>>>>> used for DMA access. The USB driver allocate the DMA buffers coherently
>>>>> and pass the DMA address to the URBs during its initialization.
>>>>> As far as Linux is concerned, how the DMA action being taking place for
>>>>> USB devices. As per my understanding, the USB host controller is taking
>>>>> care of the DMA operations. But I require a little more insight into it.
>>>> Why, what exactly are you concerned about?  What are you trying to do?
>>> Also, you _have_ read the USB DMA documentation, right?
>>>
>>> What about the documentation in this area is unclear?
>> Yes, I have read the documentation and its fine. I am mostly concerned about
>> the all the heavy lifting happening in the background.
> Why?  What exactly are you "concerned" about?  What hardware controller?
> Is something not working properly?
Everything is fine. This is more of a theoretical understanding.
>
> greg k-h


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DMA over USB

[Raghavendra]

On Wednesday 02 July 2014 11:05 AM, Chan Kim wrote:
> Hi Raghavendra,
> In my case, we used USB host design from opencore. And the driver (I don't know where it came from. it's similar to sl811-hcd.c from cypress) writes or reads the data to /from the USB host. Not using DMA. I think if the USB host has DMA capability, tha pio read/write should be chnaged to triggering DMA.
> http://lxr.free-electrons.com/source/drivers/usb/host/sl811-hcd.c  see line 234.
> Chan
>
>
>
> ?? ?? : "Raghavendra" <arrao@cdac.in>
> ?? ?? : 2014-07-02 14:20:42 ( +09:00 )
> ?? ?? : kernelnewbies <Kernelnewbies@kernelnewbies.org>
> ?? : 
> ?? : DMA over USB
>
> Hello,
>
> I have a query regarding DMA(Direct Memory Access) for the usb devices.
>
> The understanding of DMA actions over PCI is straight forward. PCI 
> devices support bus mastering capability, such that the PCI devices 
> could take the ownership of the bus and perform access to the memory 
> directly, and a software support exists for the same in Linux.
>
> As far as USB devices are concerned, they don?t have the bus mastering 
> capability like the PCI devices.
> But the USB URB structure have a field named 'dma_addr_t transfer_dma', 
> used for DMA access. The USB driver allocate the DMA buffers coherently 
> and pass the DMA address to the URBs during its initialization.
> As far as Linux is concerned, how the DMA action being taking place for 
> USB devices. As per my understanding, the USB host controller is taking 
> care of the DMA operations. But I require a little more insight into it.
>
> Further more, if it is possible for the USB devices, then can this 
> support be also extended towards low-end protocols such as I2C or SPI?
>
> Thanks,
> Raghavendra
>
> -------------------------------------------------------------------------------------------------------------------------------
> [ C-DAC is on Social-Media too. Kindly follow us at:
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> This e-mail is for the sole use of the intended recipient(s) and may
> contain confidential and privileged information. If you are not the
> intended recipient, please contact the sender by reply e-mail and destroy
> all copies and the original message. Any unauthorized review, use,
> disclosure, dissemination, forwarding, printing or copying of this email
> is strictly prohibited and appropriate legal action will be taken.
> -------------------------------------------------------------------------------------------------------------------------------
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
Thanks Chan.

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DMA over USB

[Greg KH]

On Wed, Jul 02, 2014 at 11:32:47AM +0530, Raghavendra wrote:
> On Wednesday 02 July 2014 11:02 AM, Greg KH wrote:
> >On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
> >>On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
> >>>Hello,
> >>>
> >>>I have a query regarding DMA(Direct Memory Access) for the usb devices.
> >>>
> >>>The understanding of DMA actions over PCI is straight forward. PCI
> >>>devices support bus mastering capability, such that the PCI devices
> >>>could take the ownership of the bus and perform access to the memory
> >>>directly, and a software support exists for the same in Linux.
> >>>
> >>>As far as USB devices are concerned, they don?t have the bus mastering
> >>>capability like the PCI devices.
> >>>But the USB URB structure have a field named 'dma_addr_t transfer_dma',
> >>>used for DMA access. The USB driver allocate the DMA buffers coherently
> >>>and pass the DMA address to the URBs during its initialization.
> >>>As far as Linux is concerned, how the DMA action being taking place for
> >>>USB devices. As per my understanding, the USB host controller is taking
> >>>care of the DMA operations. But I require a little more insight into it.
> >>Why, what exactly are you concerned about?  What are you trying to do?
> >Also, you _have_ read the USB DMA documentation, right?
> >
> >What about the documentation in this area is unclear?
> Yes, I have read the documentation and its fine. I am mostly concerned about
> the all the heavy lifting happening in the background.

Why?  What exactly are you "concerned" about?  What hardware controller?
Is something not working properly?

greg k-h

DMA over USB

[Greg KH]

On Wed, Jul 02, 2014 at 11:39:36AM +0530, Raghavendra wrote:
> On Wednesday 02 July 2014 11:42 AM, Greg KH wrote:
> >On Wed, Jul 02, 2014 at 11:32:47AM +0530, Raghavendra wrote:
> >>On Wednesday 02 July 2014 11:02 AM, Greg KH wrote:
> >>>On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
> >>>>On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
> >>>>>Hello,
> >>>>>
> >>>>>I have a query regarding DMA(Direct Memory Access) for the usb devices.
> >>>>>
> >>>>>The understanding of DMA actions over PCI is straight forward. PCI
> >>>>>devices support bus mastering capability, such that the PCI devices
> >>>>>could take the ownership of the bus and perform access to the memory
> >>>>>directly, and a software support exists for the same in Linux.
> >>>>>
> >>>>>As far as USB devices are concerned, they don?t have the bus mastering
> >>>>>capability like the PCI devices.
> >>>>>But the USB URB structure have a field named 'dma_addr_t transfer_dma',
> >>>>>used for DMA access. The USB driver allocate the DMA buffers coherently
> >>>>>and pass the DMA address to the URBs during its initialization.
> >>>>>As far as Linux is concerned, how the DMA action being taking place for
> >>>>>USB devices. As per my understanding, the USB host controller is taking
> >>>>>care of the DMA operations. But I require a little more insight into it.
> >>>>Why, what exactly are you concerned about?  What are you trying to do?
> >>>Also, you _have_ read the USB DMA documentation, right?
> >>>
> >>>What about the documentation in this area is unclear?
> >>Yes, I have read the documentation and its fine. I am mostly concerned about
> >>the all the heavy lifting happening in the background.
> >Why?  What exactly are you "concerned" about?  What hardware controller?
> >Is something not working properly?
> Everything is fine. This is more of a theoretical understanding.

The code is there for your theoretical research :)

DMA over USB

[Raghavendra]

On Wednesday 02 July 2014 11:55 AM, Greg KH wrote:
> On Wed, Jul 02, 2014 at 11:39:36AM +0530, Raghavendra wrote:
>> On Wednesday 02 July 2014 11:42 AM, Greg KH wrote:
>>> On Wed, Jul 02, 2014 at 11:32:47AM +0530, Raghavendra wrote:
>>>> On Wednesday 02 July 2014 11:02 AM, Greg KH wrote:
>>>>> On Tue, Jul 01, 2014 at 10:29:39PM -0700, Greg KH wrote:
>>>>>> On Wed, Jul 02, 2014 at 10:40:21AM +0530, Raghavendra wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> I have a query regarding DMA(Direct Memory Access) for the usb devices.
>>>>>>>
>>>>>>> The understanding of DMA actions over PCI is straight forward. PCI
>>>>>>> devices support bus mastering capability, such that the PCI devices
>>>>>>> could take the ownership of the bus and perform access to the memory
>>>>>>> directly, and a software support exists for the same in Linux.
>>>>>>>
>>>>>>> As far as USB devices are concerned, they don?t have the bus mastering
>>>>>>> capability like the PCI devices.
>>>>>>> But the USB URB structure have a field named 'dma_addr_t transfer_dma',
>>>>>>> used for DMA access. The USB driver allocate the DMA buffers coherently
>>>>>>> and pass the DMA address to the URBs during its initialization.
>>>>>>> As far as Linux is concerned, how the DMA action being taking place for
>>>>>>> USB devices. As per my understanding, the USB host controller is taking
>>>>>>> care of the DMA operations. But I require a little more insight into it.
>>>>>> Why, what exactly are you concerned about?  What are you trying to do?
>>>>> Also, you _have_ read the USB DMA documentation, right?
>>>>>
>>>>> What about the documentation in this area is unclear?
>>>> Yes, I have read the documentation and its fine. I am mostly concerned about
>>>> the all the heavy lifting happening in the background.
>>> Why?  What exactly are you "concerned" about?  What hardware controller?
>>> Is something not working properly?
>> Everything is fine. This is more of a theoretical understanding.
> The code is there for your theoretical research :)
Ok thanks Greg. I shall look forward to it.

Regards,
Raghavendra

-------------------------------------------------------------------------------------------------------------------------------
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