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? Best regards Michael. -- 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
