On Mon, 21 Mar 2011, Michael Hunold wrote: > Hello, > > I have been working recently on a ARM926-based SoC, which has an > OHCI-USB with only a small-amount of SRAM. At the moment, only 8kB of > SRAM are available to the OHCI-USB. > > I have found the comments before hcd_alloc_coherent(), used the > HCD_LOCAL_MEM flag accordingly and hacked dma_alloc_coherent() so that > it provides the right memory. > > Basically this is working fine and simple devices like keyboard and > mouse work without problems. > > Now I tried a couple of WiFi USB adapters and ran into a problem. > > Most of the drivers try to allocate huge amounts of buffers for transmit > queues in their init function and call usb_submit_urb() for them. > Ultimately, this triggers a memory allocation from the SRAM, which is of > course quickly exhausted already at driver init time. > > If I understand it correctly, the "problem" is in the way the devices > were designed: they don't have local memory from where data is read, but > they somehow use pre-allocated buffers in main memory (in my case the > SRAM memory). > > If this is so, then these devices will never work with OHCI-USBs that > only have a small amount of SRAM attached. > > Is that correct? More or less, yes. The devices won't work unless their drivers are re-written to allocate less memory for buffers. Alan Stern -- 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
