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SubjectRe: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support
From
Hi,

On Thu, Apr 17, 2014 at 1:38 AM, Paul Zimmerman
<Paul.Zimmerman@synopsys.com> wrote:
>> From: linux-usb-owner@vger.kernel.org [mailto:linux-usb-owner@vger.kernel.org] 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@ti.com> 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.

Yes. It is obvious that this logic is buggy, will change this.

Thanks,
Sundeep.B.S.
>
> --
> Paul
>


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