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Message-ID: <20131029154519.GB9266@roeck-us.net>
Date: Tue, 29 Oct 2013 08:45:19 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Boris BREZILLON <b.brezillon@...rkiz.com>
Cc: Wim Van Sebroeck <wim@...ana.be>,
Fabio Porcedda <fabio.porcedda@...il.com>,
Nicolas Ferre <nicolas.ferre@...el.com>,
Guenter Roeck <groeck7@...il.com>,
Yang Wenyou <wenyou.yang@...el.com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-watchdog@...r.kernel.org
Subject: Re: [PATCH] watchdog: at91sam9_wdt: various fixes
On Tue, Oct 29, 2013 at 11:37:33AM +0100, Boris BREZILLON wrote:
> Fix the secs_to_ticks macro in case 0 is passed as an argument.
>
> Rework the heartbeat calculation to increase the security margin of the
> watchdog reset timer.
>
> Use the min_heartbeat value instead of the calculated heartbeat value for
> the first watchdog reset.
>
> Signed-off-by: Boris BREZILLON <b.brezillon@...rkiz.com>
Hi Boris,
can you possibly split the three changes into separate patches ?
The first is a no-brainer. Gives my opinion of my code review capabilities
a slight damper ;-).
For the other two problems, it might make sense to describe
the problems you are trying to solve.
Couple of comments inline.
Thanks,
Guenter
> ---
> drivers/watchdog/at91sam9_wdt.c | 35 ++++++++++++++++++++++++-----------
> 1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
> index 9bd089e..f1b59f1 100644
> --- a/drivers/watchdog/at91sam9_wdt.c
> +++ b/drivers/watchdog/at91sam9_wdt.c
> @@ -51,7 +51,7 @@
> #define ticks_to_hz_rounddown(t) ((((t) + 1) * HZ) >> 8)
> #define ticks_to_hz_roundup(t) (((((t) + 1) * HZ) + 255) >> 8)
> #define ticks_to_secs(t) (((t) + 1) >> 8)
> -#define secs_to_ticks(s) (((s) << 8) - 1)
> +#define secs_to_ticks(s) (s ? (((s) << 8) - 1) : 0)
>
(s)
> #define WDT_MR_RESET 0x3FFF2FFF
>
> @@ -61,6 +61,11 @@
> /* Watchdog max delta/value in secs */
> #define WDT_COUNTER_MAX_SECS ticks_to_secs(WDT_COUNTER_MAX_TICKS)
>
> +/* Watchdog heartbeat shift used for security margin:
> + * we'll try to rshift the heartbeat value with this value to secure
> + * the watchdog reset. */
> +#define WDT_HEARTBEAT_SHIFT 2
> +
> /* Hardware timeout in seconds */
> #define WDT_HW_TIMEOUT 2
>
> @@ -158,7 +163,9 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
> int err;
> u32 mask = wdt->mr_mask;
> unsigned long min_heartbeat = 1;
> + unsigned long max_heartbeat;
> struct device *dev = &pdev->dev;
> + int shift;
>
> tmp = wdt_read(wdt, AT91_WDT_MR);
> if ((tmp & mask) != (wdt->mr & mask)) {
> @@ -181,23 +188,27 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
> if (delta < value)
> min_heartbeat = ticks_to_hz_roundup(value - delta);
>
> - wdt->heartbeat = ticks_to_hz_rounddown(value);
> - if (!wdt->heartbeat) {
> + max_heartbeat = ticks_to_hz_rounddown(value);
> + if (!max_heartbeat) {
> dev_err(dev,
> "heartbeat is too small for the system to handle it correctly\n");
> return -EINVAL;
> }
>
> - if (wdt->heartbeat < min_heartbeat + 4) {
> + for (shift = WDT_HEARTBEAT_SHIFT; shift > 0; shift--) {
> + if ((max_heartbeat >> shift) < min_heartbeat)
> + continue;
> +
> + wdt->heartbeat = max_heartbeat >> shift;
> + break;
> + }
> +
> + if (!shift)
> wdt->heartbeat = min_heartbeat;
Correct me if I am wrong, but it seems to me that
if ((max_heartbeat >> 2) >= min_heartbeat)
wdt->heartbeat = max_heartbeat >> 2;
else if ((max_heartbeat >> 1) >= min_heartbeat)
wdt->heartbeat = max_heartbeat >> 1;
else
wdt->heartbeat = min_heartbeat;
would accomplish the same and be easier to understand.
However, given that, I wonder if it is really necessary to bail out above if
max_heartbeat is 0. After all, you set heartbeat to min_heartbeat anyway
in this case.
> +
> + if (max_heartbeat < min_heartbeat + 4)
> dev_warn(dev,
> "min heartbeat and max heartbeat might be too close for the system to handle it correctly\n");
> - if (wdt->heartbeat < 4)
> - dev_warn(dev,
> - "heartbeat might be too small for the system to handle it correctly\n");
> - } else {
> - wdt->heartbeat -= 4;
> - }
>
> if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) {
> err = request_irq(wdt->irq, wdt_interrupt,
> @@ -213,7 +224,9 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
> tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask);
>
> setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt);
> - mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
> + /* Use min_heartbeat the first time because the watchdog timer might
> + * be running for a long time when we reach this init function. */
/*
* Multi-line comment style
*
* Not really sure I understand what this accomplishes. What problem
* are you trying to solve here ?
*/
> + mod_timer(&wdt->timer, jiffies + min_heartbeat);
>
> /* Try to set timeout from device tree first */
> if (watchdog_init_timeout(&wdt->wdd, 0, dev))
> --
> 1.7.9.5
>
> --
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