From: greg@kroah.com (Greg KH)
To: kernelnewbies@lists.kernelnewbies.org
Subject: DMA over USB
Date: Tue, 1 Jul 2014 23:12:41 -0700 [thread overview]
Message-ID: <20140702061241.GA945@kroah.com> (raw)
In-Reply-To: <53B3A087.1090305@cdac.in>
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
next prev parent reply other threads:[~2014-07-02 6:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-02 5:10 DMA over USB Raghavendra
2014-07-02 5:25 ` Mandeep Sandhu
2014-07-02 5:29 ` Greg KH
2014-07-02 5:32 ` Greg KH
2014-07-02 6:02 ` Raghavendra
2014-07-02 6:12 ` Greg KH [this message]
2014-07-02 6:09 ` Raghavendra
2014-07-02 6:25 ` Greg KH
2014-07-02 6:29 ` Raghavendra
2014-07-02 5:35 ` Chan Kim
2014-07-02 6:12 ` Raghavendra
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