as proposed on tech-kern@.
While all DMA memory used in the USB framework is mapped BUS_DMAMAP_COHERENT
(including data memory, which is memcpy'd from/to USB-private buffers),
the CPU can reorder loads or stores from/to main memory, causing the
controller to have an incoherent view of the DMA descriptors lists for a
short time. bus_dmamap_sync() should contain memory barriers that prevents
the CPU from reordering load/store. Note that BUS_DMAMAP_COHERENT is
still required for the DMA descriptor lists - these can't work properly
with software cache coherency.
This fixes "host controller process error/host controller halted" errors
I'm occasionally seeing with a umodem device on uhci on x86.
Thanks to Michael Lorenz for testing it on his O2, and Izumi Tsutsui on
his Cobalt Qube 2700.
in the wanted bus_dma space. If an allocation fails during operation
(i.e. when hotplugging an umass device), fall back to using the reserve.
The amount can be configured as USB_MEM_RESERVE. The default value is
256k.
Ideally, there would be a way to steal pages in the desired area from
UVM, but that's far more complicated, and this is not intrusive, plus
it works.
the device driver instead of happening automagically in the HC driver.
This affects both the HC-USBD interface as well as the USBD-device
interface.
This change will allow DMA buffers to be reused e.g. in isochronous
traffic.
Add isochronous support to the UHCI driver (not for OHCI yet).
