[2/4] usb: dwc3: gadget: check if dep->frame_number is still valid

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Felipe,

(CC'ing Kieran)

Thank you for the patch.

On Monday, 20 August 2018 13:29:59 EEST Felipe Balbi wrote:
> Gadget driver may take an unbounded amount of time to queue requests
> after XferNotReady. This is important for isochronous endpoints which
> need to be started for a specific (micro-)frame.
> 
> Before kicking the transfer, let's check if current frame number is
> still less than our aligned frame number that we got from the
> previous XferNotReady. If it isn't, then we'll increment
> dep->frame_number to make sure it's ahead of current frame number.
> 
> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
> ---
>  drivers/usb/dwc3/core.h   |  2 ++
>  drivers/usb/dwc3/gadget.c | 11 +++++++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index 285ce0ef3b91..3acf8788a680 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -685,6 +685,8 @@ struct dwc3_ep {
>  	u8			type;
>  	u8			resource_index;
>  	u32			frame_number;
> +#define DWC3_EP_FRAME_NUMBER_MASK 0x3fff
> +
>  	u32			interval;
> 
>  	char			name[20];
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index f61a4250c883..0bac9b02f28b 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1257,6 +1257,9 @@ static int __dwc3_gadget_get_frame(struct dwc3 *dwc)
> 
>  static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
>  {
> +	u16 current_frame_number;
> +	u16 frame_number;
> +
>  	if (list_empty(&dep->pending_list)) {
>  		dev_info(dep->dwc->dev, "%s: ran out of requests\n",
>  				dep->name);
> @@ -1265,6 +1268,14 @@ static int __dwc3_gadget_start_isoc(struct dwc3_ep
> *dep) }
> 
>  	dep->frame_number = DWC3_ALIGN_FRAME(dep);
> +	current_frame_number = __dwc3_gadget_get_frame(dep->dwc);
> +	frame_number = dep->frame_number & DWC3_EP_FRAME_NUMBER_MASK;
> +
> +	if (frame_number <= current_frame_number) {
> +		dep->frame_number += current_frame_number - frame_number;
> +		dep->frame_number = DWC3_ALIGN_FRAME(dep);
> +	}
> +

This greatly improves the situation with the UVC function driver. However, 
we're still receiving errors from time to time related to missed transfer 
intervals, and those errors tend to occur in bursts. Kieran should be able to 
provide you with more information. Before acking this patch I would thus like 
to make sure that we're not missing part of the problem.

>  	return __dwc3_gadget_kick_transfer(dep);
>  }