Hello. On 20-10-2011 13:52, Javier Martinez Canillas wrote:
Sorry if this is not the right place to ask this. But I didn't find an USB user mailing list.
We have a custom TI DM3730 board using a Mentor Graphics's USB controller (musb_hdrc). We are using the usb ethernet gadget (g_ether) to create a point-to-point ethernet network between the board and a host PC.
The problem is that even when the bus is USB 2.0 with a theoretical transfer rate of 480 Mbps, we are only getting about 55 Mbps from the host to the target and about 65 Mbps from the target to the host.
We are pretty sure that the board can handle more traffic than that since with a fast Ethernet 100BASE-TX connection we get about 93 Mbps.
Is correct to get so low traffic with the usb ethernet gadget?
with MUSB, yes :-s
Sorry. The problem is that it has so many silicon issues that the very powerful mode1 DMA can't be used in all situations. Also, in case of ethernet packets, we will get unaligned buffers, which MUSB's internal DMA engine can't handle, then that packet has to be transferred via PIO.
I don't think there's anything which could be done in this case :-(
I forgot to tell you more about our environment. We are using an Arago project v2.6.37 kernel for OMAP3 devices.
We took this approach because we need some DSP specific out-of-tree modules provided by TI (cmemk.ko and dsplinkk.ko) and these modules compile and work with this kernel but not with mainline.
This v2.6.37 kernel has some patches that workarounds the unaligned buffers MUSB's DMA limitation by not using this engine and using the system DMA. I thought these were in mainline too but now looking the git log I realized that they weren't pushed upstream.
They were pushed but weren't accepted, IIRC. At least I remember the patches posted there that made use of SDMA to fall back from Inventra DMA.
Thank you and best regards,
WBR, Sergei -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
