Date:	Fri,  5 Dec 2008 10:55:20 -0800
From:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
To:	netdev@...r.kernel.org
Cc:	wimax@...uxwimax.org, greg@...ah.com
Subject: [PATCH 27/40] i2400m/USB: error density tracking

This is a simple framework for tracking the amount of soft-errors in
time, so that if they go over a certain threshold they can be
considered hard errors and recovery started (instead of just
retrying).

We use this in the USB driver -- some of the USB errors are considered
soft and retried.

Signed-off-by: Inaky Perez-Gonzalez <inaky@...ux.intel.com>
---
 drivers/net/wimax/i2400m/edc.h |   90 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 90 insertions(+), 0 deletions(-)
 create mode 100644 drivers/net/wimax/i2400m/edc.h

diff --git a/drivers/net/wimax/i2400m/edc.h b/drivers/net/wimax/i2400m/edc.h
new file mode 100644
index 0000000..714540f
--- /dev/null
+++ b/drivers/net/wimax/i2400m/edc.h
@@ -0,0 +1,90 @@
+/*
+ * Intel Wireless WiMAX Connection 2400m
+ * Error Density Count: cheapo error density (over time) counter
+ *
+ *
+ * Copyright (C) 2005-2007 Intel Corporation <linux-wimax@...el.com>
+ * Reinette Chatre <reinette.chatre@...el.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version
+ * 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ *
+ * Embed an 'struct edc' somewhere. Each time there is a soft or
+ * retryable error, call edc_inc() and check if the error top
+ * watermark has been reached.
+ */
+
+#ifndef __EDC_H__
+#define __EDC_H__
+
+enum {
+	EDC_MAX_ERRORS = 10,
+	EDC_ERROR_TIMEFRAME = HZ,
+};
+
+/* error density counter */
+struct edc {
+	unsigned long timestart;
+	u16 errorcount;
+};
+
+static inline void edc_init(struct edc *edc)
+{
+	edc->timestart = jiffies;
+}
+
+/**
+ * edc_inc - report a soft error and check if we are over the watermark
+ *
+ * @edc: pointer to error density counter.
+ * @max_err: maximum number of errors we can accept over the timeframe
+ * @timeframe: lenght of the timeframe (in jiffies).
+ *
+ * Returns: !0 1 if maximum acceptable errors per timeframe has been
+ *     exceeded. 0 otherwise.
+ *
+ * This is way to determine if the number of acceptable errors per time
+ * period has been exceeded. It is not accurate as there are cases in which
+ * this scheme will not work, for example if there are periodic occurences
+ * of errors that straddle updates to the start time. This scheme is
+ * sufficient for our usage.
+ *
+ * To use, embed a 'struct edc' somewhere, initialize it with
+ * edc_init() and when an error hits:
+ *
+ * if (do_something_fails_with_a_soft_error) {
+ *        if (edc_inc(&my->edc, MAX_ERRORS, MAX_TIMEFRAME))
+ * 	           Ops, hard error, do something about it
+ *        else
+ *                 Retry or ignore, depending on whatever
+ * }
+ */
+static inline int edc_inc(struct edc *edc, u16 max_err, u16 timeframe)
+{
+	unsigned long now;
+
+	now = jiffies;
+	if (now - edc->timestart > timeframe) {
+		edc->errorcount = 1;
+		edc->timestart = now;
+	} else if (++edc->errorcount > max_err) {
+		edc->errorcount = 0;
+		edc->timestart = now;
+		return 1;
+	}
+	return 0;
+}
+
+#endif /* #ifndef __EDC_H__ */
-- 
1.5.6.5

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