From: greg@kroah.com (Greg KH)
To: kernelnewbies@lists.kernelnewbies.org
Subject: DMA over USB
Date: Tue, 1 Jul 2014 22:29:39 -0700 [thread overview]
Message-ID: <20140702052939.GB7080@kroah.com> (raw)
In-Reply-To: <53B3943D.5050408@cdac.in>
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
next prev parent reply other threads:[~2014-07-02 5:29 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 [this message]
2014-07-02 5:32 ` Greg KH
2014-07-02 6:02 ` Raghavendra
2014-07-02 6:12 ` Greg KH
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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