usb: octeon-hcd: keep SOF interrupts while a periodic pipe is due

cvmx_usb_schedule() now sleeps on an hrtimer until the nearest future periodic deadline instead of counting frames down on every SOF. The scan that finds that deadline only looks at pipes with

	next_tx_frame > usb->frame_number

which is right for picking the deadline, but it means a periodic pipe that is already due and was *not* started is invisible to the decision. A pipe can be due and not started for reasons that resolve on their own:
no idle hardware channel this round, its split window is closed (cvmx_usb_find_ready_pipe() rejects both), or another pipe owns usb->active_split.

Such a pipe is only retried from a SOF - cvmx_usb_next_pipe() looks at the isochronous and interrupt lists only when is_sof is true - so when some other periodic pipe sets a far deadline, the driver masks SOF, arms the timer for that far deadline and the due pipe waits for it. With a hub's status pipe as the far one, that is hundreds of frames; the code allows up to 8000 (one second) before it falls back to SOF.

Before the hrtimer this could not happen: any pipe with a future deadline set need_sof, so SOF stayed enabled every frame and the due pipe was retried on the next one.

Note the pipe that is due and not started, and keep SOF enabled in that case, exactly as the old code did. Nothing changes when no periodic pipe is due, which is the case the timer was added for.

Control and bulk pipes are excluded deliberately: their next_tx_frame is not updated on completion, so they are almost always "due" and would keep SOF enabled permanently.

---
Resend of
https://lore.kernel.org/all/[email protected]/
with no code change; the Assisted-by tag is now in the form coding-assistants.rst documents.

@@ -1923,6 +1923,7 @@ static void cvmx_usb_schedule(struct octeon_hcd *usb, int is_sof)
 	struct cvmx_usb_pipe *pipe;
 	int need_sof;
 	u64 min_due;
+	bool due_now;
 	enum cvmx_usb_transfer ttype;
 
 	if (usb->init_flags & CVMX_USB_INITIALIZE_FLAGS_NO_DMA) {

@@ -1964,12 +1965,23 @@ done:
 	 */
 	need_sof = 0;
 	min_due = ~0ull;
+	due_now = false;
 	for (ttype = CVMX_USB_TRANSFER_CONTROL;
 	     ttype <= CVMX_USB_TRANSFER_INTERRUPT; ttype++) {
 		list_for_each_entry(pipe, &usb->active_pipes[ttype], node) {
-			if (pipe->next_tx_frame > usb->frame_number &&
-			    pipe->next_tx_frame < min_due)
+			if (pipe->next_tx_frame <= usb->frame_number) {
+				/*
+				 * A periodic pipe that is due but was not
+				 * started - no idle channel, or its split
+				 * window is closed - is only retried from a
+				 * SOF, so do not sleep past it.
+				 */
+				if (ttype == CVMX_USB_TRANSFER_ISOCHRONOUS ||
+				    ttype == CVMX_USB_TRANSFER_INTERRUPT)
+					due_now = true;
+			} else if (pipe->next_tx_frame < min_due) {
 				min_due = pipe->next_tx_frame;
+			}
 		}
 	}
 	if (min_due != ~0ull) {

@@ -1983,7 +1995,7 @@ done:
 		 * a few frames. Stay well below the 16383-frame wrap of
 		 * HFNUM. One (micro)frame is 125us in high-speed mode.
 		 */
-		if (delta <= 4 || delta > 8000)
+		if (due_now || delta <= 4 || delta > 8000)
 			need_sof = 1;
 		else
 			hrtimer_start(&usb->sof_timer,

2.47.0

cvmx_usb_schedule() now sleeps on an hrtimer until the nearest future periodic deadline instead of counting frames down on every SOF. The scan that finds that deadline only looks at pipes with

	next_tx_frame > usb->frame_number

which is right for picking the deadline, but two kinds of pipe that need a SOF to make progress are invisible to the decision:

- A periodic pipe that is due and was *not* started: no idle hardware channel this round, its split window is closed (cvmx_usb_find_ready_pipe() rejects both), or another pipe owns usb->active_split. cvmx_usb_next_pipe() looks at the isochronous and interrupt lists only when is_sof is true.

- Any pipe that has sent its start split and waits for the frame its split complete may go out in (split_sc_frame, also checked by cvmx_usb_find_ready_pipe()). A control or bulk pipe on a full or low speed device behind a hub is in this state between its two halves, and with SOF masked nothing guarantees an interrupt that brings frame_number there.

When some other periodic pipe sets a far deadline - a hub's status pipe, whenever a hub is attached - the driver masks SOF, arms the timer for that deadline and these pipes wait for it. That is hundreds of frames; the code allows up to 8000 (one second) before it falls back to SOF.

Before the hrtimer this could not happen: any pipe with a future deadline set need_sof, so SOF stayed enabled every frame and the pipe was retried on the next one.

Note such a pipe and keep SOF enabled while there is one, whether or not another pipe has a future deadline. Nothing changes when there is none, which is the case the timer was added for.

Other control and bulk pipes are excluded deliberately: their next_tx_frame is not updated on completion, so they are almost always "due" and would keep SOF enabled permanently.

---
v2: the Sashiko review bot found that v1 missed two cases:
- due_now was only looked at when some pipe had a future deadline, so a due pipe with none still left SOF masked;
- a control or bulk pipe waiting for its split complete is in the same position as a due periodic pipe, but v1 excluded all control and bulk pipes. split_sc_frame tells these apart from the always-due ones.
Compile-tested only: there is no full or low speed device behind a hub on the test board, so the split path is not exercised.
v1: https://lore.kernel.org/all/[email protected]/

    and the resend [email protected]

index 256e459..9477a1d 100644
@@ -1923,6 +1923,7 @@ static void cvmx_usb_schedule(struct octeon_hcd *usb, int is_sof)
 	struct cvmx_usb_pipe *pipe;
 	int need_sof;
 	u64 min_due;
+	bool due_now;
 	enum cvmx_usb_transfer ttype;
 
 	if (usb->init_flags & CVMX_USB_INITIALIZE_FLAGS_NO_DMA) {

@@ -1964,15 +1965,32 @@ done:
 	 */
 	need_sof = 0;
 	min_due = ~0ull;
+	due_now = false;
 	for (ttype = CVMX_USB_TRANSFER_CONTROL;
 	     ttype <= CVMX_USB_TRANSFER_INTERRUPT; ttype++) {
 		list_for_each_entry(pipe, &usb->active_pipes[ttype], node) {
+			/*
+			 * Do not sleep past a pipe that is only retried from a
+			 * SOF: a periodic one that is due but was not started
+			 * (no idle channel, closed split window, another pipe's
+			 * split active), or any pipe waiting for the frame its
+			 * split complete may go out in. Other control and bulk
+			 * pipes are left out: their next_tx_frame is not updated
+			 * on completion, so they always look due.
+			 */
+			if (pipe->split_sc_frame != -1 ||
+			    (pipe->next_tx_frame <= usb->frame_number &&
+			     (ttype == CVMX_USB_TRANSFER_ISOCHRONOUS ||
+			      ttype == CVMX_USB_TRANSFER_INTERRUPT)))
+				due_now = true;
 			if (pipe->next_tx_frame > usb->frame_number &&
 			    pipe->next_tx_frame < min_due)
 				min_due = pipe->next_tx_frame;
 		}
 	}
-	if (min_due != ~0ull) {
+	if (due_now) {
+		need_sof = 1;
+	} else if (min_due != ~0ull) {
 		u64 delta = min_due - usb->frame_number;
 
 		/*