> From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of sundeep subbaraya > Sent: Wednesday, April 16, 2014 3:39 AM > > Hi Felipe, > > On Thu, Apr 3, 2014 at 8:28 PM, Felipe Balbi <balbi@xxxxxx> wrote: > > >> +static int start_dma(struct xusb_ep *ep, u32 src, u32 dst, u32 length) > > > > please prepend this with xudc_, it makes tracing a lot easier. > > > >> +{ > >> + struct xusb_udc *udc; > >> + int rc = 0; > >> + unsigned long timeout; > >> + > >> + udc = ep->udc; > >> + /* > >> + * Set the addresses in the DMA source and > >> + * destination registers and then set the length > >> + * into the DMA length register. > >> + */ > >> + udc->write_fn(udc->base_address, XUSB_DMA_DSAR_ADDR_OFFSET, src); > >> + udc->write_fn(udc->base_address, XUSB_DMA_DDAR_ADDR_OFFSET, dst); > >> + udc->write_fn(udc->base_address, XUSB_DMA_LENGTH_OFFSET, length); > >> + > >> + /* > >> + * Wait till DMA transaction is complete and > >> + * check whether the DMA transaction was > >> + * successful. > >> + */ > >> + while ((udc->read_fn(ep->udc->base_address + XUSB_DMA_STATUS_OFFSET) & > >> + XUSB_DMA_DMASR_BUSY) == XUSB_DMA_DMASR_BUSY) { > >> + timeout = jiffies + 10000; > >> + > >> + if (time_after(jiffies, timeout)) { > >> + rc = -ETIMEDOUT; > >> + goto clean; > >> + } > >> + } > > > > don't you get an IRQ for DMA completion ? If you do, you could be using > > wait_for_completion() > > This function is called in interrupt context when buffer is ready or > free. It initiates > DMA to transfer data from IP buffer to memory. Hence it waits in busy > loop till DMA > completes If this function is called in interrupt context, then you can't use jiffies for your timeout, since jiffies may not get updated while in interrupt context. -- Paul ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
