Hi Oliver, Thanks for review. On 08/31/2016 05:53 PM, Oliver Neukum wrote: > On Mon, 2016-08-29 at 13:26 +0800, Lu Baolu wrote: >> + /* >> + * Memory barrier to ensure hardware sees the trbs >> + * enqueued above. >> + */ >> + wmb(); >> + if (cycle) >> + trb->field[3] |= cpu_to_le32(cycle); >> + else >> + trb->field[3] &= cpu_to_le32(~TRB_CYCLE); > And this manipulation you don't need the hardware to see? TRB is a shared memory block between CPU and DbC hardware. TRB_CYCLE bit is the identifier of the owner. When CPU submits a transfer block to device, it populates the TRB and toggles the cycle bit in the end to let device handle it. Before toggling the cycle bit, driver must make sure 1) the compiler should not reorder the write sequence, and 2) all writes should be really take effect in memory instead of pending in the caches. That's the reason I put a wmb() before toggling the cycle bit. Best regards, Lu Baolu -- 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
