On Sat, Dec 21, 2013 at 11:03 PM, Arnd Bergmann [off-list ref] wrote:

On Saturday 21 December 2013 17:00:51 Loc Ho wrote:

quoted

On Sat, Dec 21, 2013 at 12:11 PM, Arnd Bergmann [off-list ref] wrote:

quoted

On Saturday 21 December 2013, Ravi Patel wrote:

quoted

This patch adds support for APM X-Gene SoC Queue Manager/Traffic Manager.
 QMTM is required by APM X-Gene SoC Ethernet, PktDMA (XOR Engine) and
 Security Engine subsystems. All subsystems communicate with QMTM using
 messages which include information about the work to be performed and
 the location of associated data buffers.

Please describe here what the purpose of the qmtm is, as this is not
entirely clear from the code.

In particular, please describe how this differs from a dmaengine driver
and why it is not possible to extend the dma slave API to describe qmtm
as a dma engine.

[Loc Ho]
If the QM driver implements the DMA API, what about the actual DMA
engine driver which interfaces with this QM driver. We would have DMA
client interfaces with the X-Gene DMA driver (not available yet) via
DMA API which in turn interfaces with this QM driver via DMA API.
Won't this be kind of awkward? Also, the QM only manage messages (or
descriptors) which are 32-bytes or 64-bytes. It doesn't actually do
any data transfer of various sizes.

Please describe here what the purpose of the qmtm is, as this is not
entirely clear from the code or from your reply.

Greg was guessing that it's a bus controller, my best guess is a DMA
engine. If it's something completely different, you have to let
us know what it is so we can do a proper review rather than guessing.

Please provide a link to the data sheet if you are unable to explain.

Here is URL to a text document explaining role of QMTM device with CPU, Ethernet
subsystem.

https://drive.google.com/file/d/0B28TgQZ3JLoRRGNnbjJoUGNHWW8/edit?usp=sharing

For simplicity, I have shown only Ethernet.
PktDMA and Security subsystem interfaces with QMTM in the same way as Ethernet.