Hi Felipe,
On Wed, Apr 16, 2014 at 11:32 PM, Felipe Balbi <balbi@xxxxxx> wrote:
> Hi,
>
> On Wed, Apr 16, 2014 at 04:09:28PM +0530, sundeep subbaraya wrote:
>> 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
>
> wait, so you start_dma() before your gadget driver asks you to ?
in ep_queue driver starts dma transfer from/to IP buffer to/from req->buf.
If transfer is completed then request is not added to ep request queue
and returns from ep_queue.
If transfer is not completed (actual < length) then request is added
to queue and returns from ep_queue.
when buffer processed interrupt occurs, handler starts dma if there is
request in queue and calls complete call back (when actual == length)
Hence answer is Yes for some transfers (start dma called from
interrupt handler not from ep_queue).
Thanks,
Sundeep.B.S.
>
> --
> balbi
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