Re: [PATCH v2 1/1] usb: host: xhci: update event ring dequeue pointer on purpose

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 29.9.2019 9.07, Peter Chen wrote:
> On some situations, the software handles TRB events slower
> than adding TRBs, then xhci_handle_event can't return zero
> long time, the xHC will consider the event ring is full,
> and trigger "Event Ring Full" error, but in fact, the software
> has already finished lots of events, just no chance to
> update ERDP (event ring dequeue pointer).
> 
> In this commit, we force update ERDP if half of TRBS_PER_SEGMENT
> events have handled to avoid "Event Ring Full" error.
> 
> Signed-off-by: Peter Chen <peter.chen@nxp.com>
> ---
> Changes for v2:
> - If current ERDP value is the same with intended written one,
>    give up this written.
> 
>   drivers/usb/host/xhci-ring.c | 62 ++++++++++++++++++++++++++----------
>   1 file changed, 45 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index e220bcbee173..2c0a15c3b3a7 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -2737,6 +2737,44 @@ static int xhci_handle_event(struct xhci_hcd *xhci)
>   	return 1;
>   }
>   
> +/*
> + * Update Event Ring Dequeue Pointer:
> + * - When all events have finished
> + * - To avoid "Event Ring Full Error" condition
> + */
> +static void xhci_update_erst_dequeue(struct xhci_hcd *xhci,
> +		union xhci_trb *event_ring_deq)
> +{
> +	u64 temp_64;
> +	dma_addr_t deq;
> +
> +	temp_64 = xhci_read_64(xhci, &xhci->ir_set->erst_dequeue);
> +	/* If necessary, update the HW's version of the event ring deq ptr. */
> +	if (event_ring_deq != xhci->event_ring->dequeue) {
> +		deq = xhci_trb_virt_to_dma(xhci->event_ring->deq_seg,
> +				xhci->event_ring->dequeue);
> +		if (deq == 0)
> +			xhci_warn(xhci, "WARN something wrong with SW event "
> +					"ring dequeue ptr.\n");
> +
> +		/*
> +		 * Per 4.9.4, Software writes to the ERDP register shall
> +		 * always advance the Event Ring Dequeue Pointer value.
> +		 */
> +		if ((temp_64 & (u64) ~ERST_PTR_MASK) ==
> +				((u64) deq & (u64) ~ERST_PTR_MASK))
> +			return;
> +
> +		/* Update HC event ring dequeue pointer */
> +		temp_64 &= ERST_PTR_MASK;
> +		temp_64 |= ((u64) deq & (u64) ~ERST_PTR_MASK);
> +	}
> +
> +	/* Clear the event handler busy flag (RW1C) */
> +	temp_64 |= ERST_EHB;
> +	xhci_write_64(xhci, temp_64, &xhci->ir_set->erst_dequeue);
> +}
> +
>   /*
>    * xHCI spec says we can get an interrupt, and if the HC has an error condition,
>    * we might get bad data out of the event ring.  Section 4.10.2.7 has a list of
> @@ -2748,9 +2786,9 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
>   	union xhci_trb *event_ring_deq;
>   	irqreturn_t ret = IRQ_NONE;
>   	unsigned long flags;
> -	dma_addr_t deq;
>   	u64 temp_64;
>   	u32 status;
> +	int event_loop = 0;
>   
>   	spin_lock_irqsave(&xhci->lock, flags);
>   	/* Check if the xHC generated the interrupt, or the irq is shared */
> @@ -2804,24 +2842,14 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
>   	/* FIXME this should be a delayed service routine
>   	 * that clears the EHB.
>   	 */
> -	while (xhci_handle_event(xhci) > 0) {}
> -
> -	temp_64 = xhci_read_64(xhci, &xhci->ir_set->erst_dequeue);
> -	/* If necessary, update the HW's version of the event ring deq ptr. */
> -	if (event_ring_deq != xhci->event_ring->dequeue) {
> -		deq = xhci_trb_virt_to_dma(xhci->event_ring->deq_seg,
> -				xhci->event_ring->dequeue);
> -		if (deq == 0)
> -			xhci_warn(xhci, "WARN something wrong with SW event "
> -					"ring dequeue ptr.\n");
> -		/* Update HC event ring dequeue pointer */
> -		temp_64 &= ERST_PTR_MASK;
> -		temp_64 |= ((u64) deq & (u64) ~ERST_PTR_MASK);
> +	while (xhci_handle_event(xhci) > 0) {
> +		if (event_loop++ < TRBS_PER_SEGMENT / 2)
> +			continue;
> +		xhci_update_erst_dequeue(xhci, event_ring_deq);
> +		event_loop = 0;
>   	}
>   
> -	/* Clear the event handler busy flag (RW1C); event ring is empty. */
> -	temp_64 |= ERST_EHB;
> -	xhci_write_64(xhci, temp_64, &xhci->ir_set->erst_dequeue);
> +	xhci_update_erst_dequeue(xhci, event_ring_deq);
>   	ret = IRQ_HANDLED;
>   
>   out:
> 

This should work, adding to queue

-Mathias