xhci: Use more event ring segment table entries

Users have reported log spam created by "Event Ring Full" xHC event
TRBs. These are caused by interrupt latency in conjunction with a very
busy set of devices on the bus. The errors are benign, but throughput
will suffer as the xHC will pause processing of transfers until the
event ring is drained by the kernel. Expand the number of event TRB slots
available by increasing the number of event ring segments in the ERST.

Controllers have a hardware-defined limit as to the number of ERST
entries they can process, so make the actual number in use
min(ERST_MAX_SEGS, hw_max).

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 0a37f0d511cf53c377ac52669573086e4d5fb577..faab34d28f9a07ac811c03e9f93297a4128a0478 100644 (file)
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2239,12 +2239,17 @@ xhci_alloc_interrupter(struct xhci_hcd *xhci, gfp_t flags)
        struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
        struct xhci_interrupter *ir;
        int ret;
+       unsigned int nr_event_segs;
 
        ir = kzalloc_node(sizeof(*ir), flags, dev_to_node(dev));
        if (!ir)
                return NULL;
 
-       ir->event_ring = xhci_ring_alloc(xhci, ERST_NUM_SEGS, 1, TYPE_EVENT,
+       nr_event_segs = min_t(unsigned int,
+                             1 << HCS_ERST_MAX(xhci->hcs_params2),
+                             ERST_MAX_SEGS);
+
+       ir->event_ring = xhci_ring_alloc(xhci, nr_event_segs, 1, TYPE_EVENT,
                                        0, flags);
        if (!ir->event_ring) {
                xhci_warn(xhci, "Failed to allocate interrupter event ring\n");
@@ -2281,7 +2286,7 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
        /* set ERST count with the number of entries in the segment table */
        erst_size = readl(&ir->ir_set->erst_size);
        erst_size &= ERST_SIZE_MASK;
-       erst_size |= ERST_NUM_SEGS;
+       erst_size |= ir->event_ring->num_segs;
        writel(erst_size, &ir->ir_set->erst_size);
 
        erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 31088602c07088343701118d74d34b53852d44ae..c23b01d716478ee0c0d6d0524572741cf32a3eb1 100644 (file)
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1674,8 +1674,9 @@ struct urb_priv {
  * Each segment table entry is 4*32bits long.  1K seems like an ok size:
  * (1K bytes * 8bytes/bit) / (4*32 bits) = 64 segment entries in the table,
  * meaning 64 ring segments.
- * Initial allocated size of the ERST, in number of entries */
-#define        ERST_NUM_SEGS   1
+ */
+/* Maximum number of segments in the ERST */
+#define        ERST_MAX_SEGS   8
 /* Poll every 60 seconds */
 #define        POLL_TIMEOUT    60
 /* Stop endpoint command timeout (secs) for URB cancellation watchdog timer */