linux-kernel - Re: [PATCH v12 04/41] usb: host: xhci-mem: Cleanup pending secondary event ring events

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Date: Thu, 4 Jan 2024 16:48:19 +0200
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: Wesley Cheng <quic_wcheng@...cinc.com>, srinivas.kandagatla@...aro.org,
 mathias.nyman@...el.com, perex@...ex.cz, conor+dt@...nel.org,
 corbet@....net, gregkh@...uxfoundation.org, lgirdwood@...il.com,
 andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org,
 konrad.dybcio@...aro.org, Thinh.Nguyen@...opsys.com, broonie@...nel.org,
 bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org, agross@...nel.org
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-sound@...r.kernel.org, linux-usb@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-doc@...r.kernel.org,
 alsa-devel@...a-project.org
Subject: Re: [PATCH v12 04/41] usb: host: xhci-mem: Cleanup pending secondary
 event ring events

On 2.1.2024 23.45, Wesley Cheng wrote:
> As part of xHCI bus suspend, the XHCI is halted.  However, if there are
> pending events in the secondary event ring, it is observed that the xHCI
> controller stops responding to further commands upon host or device
> initiated bus resume.  Iterate through all pending events and update the
> dequeue pointer to the beginning of the event ring.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
...
> +/*
> + * Move the event ring dequeue pointer to skip events kept in the secondary
> + * event ring.  This is used to ensure that pending events in the ring are
> + * acknowledged, so the XHCI HCD can properly enter suspend/resume.  The
> + * secondary ring is typically maintained by an external component.
> + */
> +void xhci_skip_sec_intr_events(struct xhci_hcd *xhci,
> +	struct xhci_ring *ring,	struct xhci_interrupter *ir)
> +{
> +	union xhci_trb *erdp_trb, *current_trb;
> +	u64 erdp_reg;
> +	u32 iman_reg;
> +	dma_addr_t deq;
> +
> +	/* disable irq, ack pending interrupt and ack all pending events */
> +	xhci_disable_interrupter(ir);
> +	iman_reg = readl_relaxed(&ir->ir_set->irq_pending);
> +	if (iman_reg & IMAN_IP)
> +		writel_relaxed(iman_reg, &ir->ir_set->irq_pending);
> +
> +	/* last acked event trb is in erdp reg  */
> +	erdp_reg = xhci_read_64(xhci, &ir->ir_set->erst_dequeue);
> +	deq = (dma_addr_t)(erdp_reg & ERST_PTR_MASK);
> +	if (!deq) {
> +		xhci_err(xhci, "event ring handling not required\n");
> +		return;
> +	}
> +
> +	erdp_trb = current_trb = ir->event_ring->dequeue;
> +	/* read cycle state of the last acked trb to find out CCS */
> +	ring->cycle_state = le32_to_cpu(current_trb->event_cmd.flags) & TRB_CYCLE;
> +
> +	while (1) {
> +		inc_deq(xhci, ir->event_ring);
> +		erdp_trb = ir->event_ring->dequeue;
> +		/* cycle state transition */
> +		if ((le32_to_cpu(erdp_trb->event_cmd.flags) & TRB_CYCLE) !=
> +		    ring->cycle_state)
> +			break;
> +	}
> +
> +	xhci_update_erst_dequeue(xhci, ir, current_trb, true);
> +}

Code above is very similar to the existing event ring processing parts of xhci_irq()
and xhci_handle_event()

I'll see if I can refactor the existing event ring processing, decouple it from
event handling so that it could be used by primary and secondary interrupters with
handlers, and this case where we just want to clear the event ring.

Thanks
Mathias