xhci: dbc: Avoid event polling busyloop if pending rx transfers are inactive.

Event polling delay is set to 0 if there are any pending requests in
either rx or tx requests lists. Checking for pending requests does
not work well for "IN" transfers as the tty driver always queues
requests to the list and TRBs to the ring, preparing to receive data
from the host.

This causes unnecessary busylooping and cpu hogging.

Only set the event polling delay to 0 if there are pending tx "write"
transfers, or if it was less than 10ms since last active data transfer
in any direction.

Cc: Łukasz Bartosik <ukaszb@chromium.org>
Fixes: fb18e5bb9660 ("xhci: dbc: poll at different rate depending on data transfer activity")
Cc: stable@vger.kernel.org
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250505125630.561699-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
index fd7895b24367db81644692e8a0a0382f70cc09eb..0d4ce5734165ed3fc9b04d5901395fb4e95e6838 100644 (file)
--- a/drivers/usb/host/xhci-dbgcap.c
+++ b/drivers/usb/host/xhci-dbgcap.c
@@ -823,6 +823,7 @@ static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
 {
        dma_addr_t              deq;
        union xhci_trb          *evt;
+       enum evtreturn          ret = EVT_DONE;
        u32                     ctrl, portsc;
        bool                    update_erdp = false;
 
@@ -909,6 +910,7 @@ static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
                        break;
                case TRB_TYPE(TRB_TRANSFER):
                        dbc_handle_xfer_event(dbc, evt);
+                       ret = EVT_XFER_DONE;
                        break;
                default:
                        break;
@@ -927,7 +929,7 @@ static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
                lo_hi_writeq(deq, &dbc->regs->erdp);
        }
 
-       return EVT_DONE;
+       return ret;
 }
 
 static void xhci_dbc_handle_events(struct work_struct *work)
@@ -936,6 +938,7 @@ static void xhci_dbc_handle_events(struct work_struct *work)
        struct xhci_dbc         *dbc;
        unsigned long           flags;
        unsigned int            poll_interval;
+       unsigned long           busypoll_timelimit;
 
        dbc = container_of(to_delayed_work(work), struct xhci_dbc, event_work);
        poll_interval = dbc->poll_interval;
@@ -954,11 +957,21 @@ static void xhci_dbc_handle_events(struct work_struct *work)
                        dbc->driver->disconnect(dbc);
                break;
        case EVT_DONE:
-               /* set fast poll rate if there are pending data transfers */
+               /*
+                * Set fast poll rate if there are pending out transfers, or
+                * a transfer was recently processed
+                */
+               busypoll_timelimit = dbc->xfer_timestamp +
+                       msecs_to_jiffies(DBC_XFER_INACTIVITY_TIMEOUT);
+
                if (!list_empty(&dbc->eps[BULK_OUT].list_pending) ||
-                   !list_empty(&dbc->eps[BULK_IN].list_pending))
+                   time_is_after_jiffies(busypoll_timelimit))
                        poll_interval = 0;
                break;
+       case EVT_XFER_DONE:
+               dbc->xfer_timestamp = jiffies;
+               poll_interval = 0;
+               break;
        default:
                dev_info(dbc->dev, "stop handling dbc events\n");
                return;

diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
index 9dc8f4d8077cc424047d89de950cca11685c355c..47ac72c2286d9a42862fe7fc51067a263560feee 100644 (file)
--- a/drivers/usb/host/xhci-dbgcap.h
+++ b/drivers/usb/host/xhci-dbgcap.h
@@ -96,6 +96,7 @@ struct dbc_ep {
 #define DBC_WRITE_BUF_SIZE             8192
 #define DBC_POLL_INTERVAL_DEFAULT      64      /* milliseconds */
 #define DBC_POLL_INTERVAL_MAX          5000    /* milliseconds */
+#define DBC_XFER_INACTIVITY_TIMEOUT    10      /* milliseconds */
 /*
  * Private structure for DbC hardware state:
  */
@@ -142,6 +143,7 @@ struct xhci_dbc {
        enum dbc_state                  state;
        struct delayed_work             event_work;
        unsigned int                    poll_interval;  /* ms */
+       unsigned long                   xfer_timestamp;
        unsigned                        resume_required:1;
        struct dbc_ep                   eps[2];
 
@@ -187,6 +189,7 @@ struct dbc_request {
 enum evtreturn {
        EVT_ERR = -1,
        EVT_DONE,
+       EVT_XFER_DONE,
        EVT_GSER,
        EVT_DISC,
 };