From: Chris Brandt <Chris.Brandt@renesas.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
"linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>,
Simon Horman <horms+renesas@verge.net.au>
Subject: RE: [PATCH v2 1/2] watchdog: rza_wdt: Support longer timeouts
Date: Thu, 6 Sep 2018 21:39:30 +0000 [thread overview]
Message-ID: <TY1PR01MB1562E9684200CF49FFD095F38A010@TY1PR01MB1562.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <20180906185643.GA25704@roeck-us.net>
On Thursday, September 06, 2018, Guenter Roeck wrote:
> > > + u16 counter;
> > > +
> > > + if (priv->cks == CKS_4BIT) {
> > > + counter = DIV_ROUND_UP((timeout * rate), 4194304) + 1;
> >
> > two spaces ?
> >
> > Also, I am not sure how this prevents overflows. Was't the concern
> > that timeout * rate might overflow an int ?
Actually, I don't have to care about math overflows for large timeout
values because the driver sets a max timeout value.
if (priv->cks == CKS_4BIT) {
/* Assume slowest clock rate possible (CKS=0xF) */
priv->wdev.max_timeout = (4194304 * U8_MAX) / rate;
So if a user sends a timeout greater than that, the upper layer returns
'Invalid argument' before it ever gets to the driver.
I guess that technically means I don't really have to do the
if (counter > 256)
counter = 256;
either because I will never get a timeout value greater than my max.
(but, I might keep it in there anyway)
Chris
next prev parent reply other threads:[~2018-09-07 2:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 18:37 [PATCH v2 0/2] watchdog: Add support for RZ/A2 wdt Chris Brandt
2018-09-06 18:37 ` [PATCH v2 1/2] watchdog: rza_wdt: Support longer timeouts Chris Brandt
2018-09-06 18:52 ` Guenter Roeck
2018-09-06 18:56 ` Guenter Roeck
2018-09-06 19:40 ` Chris Brandt
2018-09-06 19:40 ` Chris Brandt
2018-09-06 21:39 ` Chris Brandt [this message]
2018-09-06 20:45 ` Chris Brandt
2018-09-06 18:37 ` [PATCH v2 2/2] dt-bindings: watchdog: renesas-wdt: Add support for R7S9210 Chris Brandt
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