From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>,
Uday M Bhat <uday.m.bhat@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15.y 2/6] xhci: dbc: poll at different rate depending on data transfer activity
Date: Mon, 27 Oct 2025 14:42:48 -0400 [thread overview]
Message-ID: <20251027184252.639069-2-sashal@kernel.org> (raw)
In-Reply-To: <20251027184252.639069-1-sashal@kernel.org>
From: Mathias Nyman <mathias.nyman@linux.intel.com>
[ Upstream commit fb18e5bb96603cc79d97f03e4c05f3992cf28624 ]
DbC driver starts polling for events immediately when DbC is enabled.
The current polling interval is 1ms, which keeps the CPU busy, impacting
power management even when there are no active data transfers.
Solve this by polling at a slower rate, with a 64ms interval as default
until a transfer request is queued, or if there are still are pending
unhandled transfers at event completion.
Tested-by: Uday M Bhat <uday.m.bhat@intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240229141438.619372-9-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: f3d12ec847b9 ("xhci: dbc: fix bogus 1024 byte prefix if ttyDBC read races with stall event")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/usb/host/xhci-dbgcap.c | 13 +++++++++++--
drivers/usb/host/xhci-dbgcap.h | 2 ++
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
index 9a1728333affa..fa4ef738d9e62 100644
--- a/drivers/usb/host/xhci-dbgcap.c
+++ b/drivers/usb/host/xhci-dbgcap.c
@@ -665,7 +665,8 @@ static int xhci_dbc_start(struct xhci_dbc *dbc)
return ret;
}
- return mod_delayed_work(system_wq, &dbc->event_work, 1);
+ return mod_delayed_work(system_wq, &dbc->event_work,
+ msecs_to_jiffies(dbc->poll_interval));
}
static void xhci_dbc_stop(struct xhci_dbc *dbc)
@@ -964,8 +965,10 @@ static void xhci_dbc_handle_events(struct work_struct *work)
enum evtreturn evtr;
struct xhci_dbc *dbc;
unsigned long flags;
+ unsigned int poll_interval;
dbc = container_of(to_delayed_work(work), struct xhci_dbc, event_work);
+ poll_interval = dbc->poll_interval;
spin_lock_irqsave(&dbc->lock, flags);
evtr = xhci_dbc_do_handle_events(dbc);
@@ -981,13 +984,18 @@ 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 */
+ if (!list_empty(&dbc->eps[BULK_OUT].list_pending) ||
+ !list_empty(&dbc->eps[BULK_IN].list_pending))
+ poll_interval = 1;
break;
default:
dev_info(dbc->dev, "stop handling dbc events\n");
return;
}
- mod_delayed_work(system_wq, &dbc->event_work, 1);
+ mod_delayed_work(system_wq, &dbc->event_work,
+ msecs_to_jiffies(poll_interval));
}
static ssize_t dbc_show(struct device *dev,
@@ -1242,6 +1250,7 @@ xhci_alloc_dbc(struct device *dev, void __iomem *base, const struct dbc_driver *
dbc->idVendor = DBC_VENDOR_ID;
dbc->bcdDevice = DBC_DEVICE_REV;
dbc->bInterfaceProtocol = DBC_PROTOCOL;
+ dbc->poll_interval = DBC_POLL_INTERVAL_DEFAULT;
if (readl(&dbc->regs->control) & DBC_CTRL_DBC_ENABLE)
goto err;
diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
index 34c20d6c9e559..86312043552df 100644
--- a/drivers/usb/host/xhci-dbgcap.h
+++ b/drivers/usb/host/xhci-dbgcap.h
@@ -93,6 +93,7 @@ struct dbc_ep {
#define DBC_QUEUE_SIZE 16
#define DBC_WRITE_BUF_SIZE 8192
+#define DBC_POLL_INTERVAL_DEFAULT 64 /* milliseconds */
/*
* Private structure for DbC hardware state:
@@ -138,6 +139,7 @@ struct xhci_dbc {
enum dbc_state state;
struct delayed_work event_work;
+ unsigned int poll_interval; /* ms */
unsigned resume_required:1;
struct dbc_ep eps[2];
--
2.51.0
next prev parent reply other threads:[~2025-10-27 18:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-27 7:20 FAILED: patch "[PATCH] xhci: dbc: fix bogus 1024 byte prefix if ttyDBC read races" failed to apply to 5.15-stable tree gregkh
2025-10-27 18:42 ` [PATCH 5.15.y 1/6] xhci: dbc: Provide sysfs option to configure dbc descriptors Sasha Levin
2025-10-27 18:42 ` Sasha Levin [this message]
2025-10-27 18:42 ` [PATCH 5.15.y 3/6] xhci: dbc: Allow users to modify DbC poll interval via sysfs Sasha Levin
2025-10-27 18:42 ` [PATCH 5.15.y 4/6] xhci: dbc: Improve performance by removing delay in transfer event polling Sasha Levin
2025-10-27 18:42 ` [PATCH 5.15.y 5/6] xhci: dbc: Avoid event polling busyloop if pending rx transfers are inactive Sasha Levin
2025-10-27 18:42 ` [PATCH 5.15.y 6/6] xhci: dbc: fix bogus 1024 byte prefix if ttyDBC read races with stall event Sasha Levin
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