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Message-ID: <20220221124405.o7vda3zaswi6ycrh@favored>
Date: Mon, 21 Feb 2022 06:44:05 -0600
From: Nishanth Menon <nm@...com>
To: Jan Kiszka <jan.kiszka@...mens.com>, Hari Nagalla <hnagalla@...com>
CC: <wim@...ux-watchdog.org>, <linux@...ck-us.net>,
<linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv4 3/4] watchdog: rti-wdt: attach to running watchdog
during probe
On 10:59-20220221, Jan Kiszka wrote:
> On 21.02.22 10:10, Jan Kiszka wrote:
> > On 17.07.20 15:29, Tero Kristo wrote:
> >> If the RTI watchdog is running already during probe, the driver must
> >> configure itself to match the HW. Window size and timeout is probed from
> >> hardware, and the last keepalive ping is adjusted to match it also.
> >>
> >> Signed-off-by: Tero Kristo <t-kristo@...com>
> >> ---
> >> drivers/watchdog/rti_wdt.c | 112 +++++++++++++++++++++++++++++++++----
> >> 1 file changed, 102 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> >> index d456dd72d99a..7cbdc178ffe8 100644
> >> --- a/drivers/watchdog/rti_wdt.c
> >> +++ b/drivers/watchdog/rti_wdt.c
> >> @@ -35,7 +35,11 @@
> >>
> >> #define RTIWWDRX_NMI 0xa
> >>
> >> -#define RTIWWDSIZE_50P 0x50
> >> +#define RTIWWDSIZE_50P 0x50
> >> +#define RTIWWDSIZE_25P 0x500
> >> +#define RTIWWDSIZE_12P5 0x5000
> >> +#define RTIWWDSIZE_6P25 0x50000
> >> +#define RTIWWDSIZE_3P125 0x500000
> >>
> >> #define WDENABLE_KEY 0xa98559da
> >>
> >> @@ -48,7 +52,7 @@
> >>
> >> #define DWDST BIT(1)
> >>
> >> -static int heartbeat;
> >> +static int heartbeat = DEFAULT_HEARTBEAT;
> >>
> >> /*
> >> * struct to hold data for each WDT device
> >> @@ -79,11 +83,9 @@ static int rti_wdt_start(struct watchdog_device *wdd)
> >> * be petted during the open window; not too early or not too late.
> >> * The HW configuration options only allow for the open window size
> >> * to be 50% or less than that; we obviouly want to configure the open
> >> - * window as large as possible so we select the 50% option. To avoid
> >> - * any glitches, we accommodate 5% safety margin also, so we setup
> >> - * the min_hw_hearbeat at 55% of the timeout period.
> >> + * window as large as possible so we select the 50% option.
> >> */
> >> - wdd->min_hw_heartbeat_ms = 11 * wdd->timeout * 1000 / 20;
> >> + wdd->min_hw_heartbeat_ms = 500 * wdd->timeout;
> >>
> >> /* Generate NMI when wdt expires */
> >> writel_relaxed(RTIWWDRX_NMI, wdt->base + RTIWWDRXCTRL);
> >> @@ -110,7 +112,48 @@ static int rti_wdt_ping(struct watchdog_device *wdd)
> >> return 0;
> >> }
> >>
> >> -static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
> >> +static int rti_wdt_setup_hw_hb(struct watchdog_device *wdd, u32 wsize)
> >> +{
> >> + /*
> >> + * RTI only supports a windowed mode, where the watchdog can only
> >> + * be petted during the open window; not too early or not too late.
> >> + * The HW configuration options only allow for the open window size
> >> + * to be 50% or less than that.
> >> + */
> >> + switch (wsize) {
> >> + case RTIWWDSIZE_50P:
> >> + /* 50% open window => 50% min heartbeat */
> >> + wdd->min_hw_heartbeat_ms = 500 * heartbeat;
> >> + break;
> >> +
> >> + case RTIWWDSIZE_25P:
> >> + /* 25% open window => 75% min heartbeat */
> >> + wdd->min_hw_heartbeat_ms = 750 * heartbeat;
> >> + break;
> >> +
> >> + case RTIWWDSIZE_12P5:
> >> + /* 12.5% open window => 87.5% min heartbeat */
> >> + wdd->min_hw_heartbeat_ms = 875 * heartbeat;
> >> + break;
> >> +
> >> + case RTIWWDSIZE_6P25:
> >> + /* 6.5% open window => 93.5% min heartbeat */
> >> + wdd->min_hw_heartbeat_ms = 935 * heartbeat;
> >> + break;
> >> +
> >> + case RTIWWDSIZE_3P125:
> >> + /* 3.125% open window => 96.9% min heartbeat */
> >> + wdd->min_hw_heartbeat_ms = 969 * heartbeat;
> >> + break;
> >> +
> >> + default:
> >> + return -EINVAL;
> >> + }
> >> +
> >> + return 0;
> >> +}
> >> +
> >> +static unsigned int rti_wdt_get_timeleft_ms(struct watchdog_device *wdd)
> >> {
> >> u64 timer_counter;
> >> u32 val;
> >> @@ -123,11 +166,18 @@ static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
> >>
> >> timer_counter = readl_relaxed(wdt->base + RTIDWDCNTR);
> >>
> >> + timer_counter *= 1000;
> >> +
> >> do_div(timer_counter, wdt->freq);
> >>
> >> return timer_counter;
> >> }
> >>
> >> +static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
> >> +{
> >> + return rti_wdt_get_timeleft_ms(wdd) / 1000;
> >> +}
> >> +
> >> static const struct watchdog_info rti_wdt_info = {
> >> .options = WDIOF_KEEPALIVEPING,
> >> .identity = "K3 RTI Watchdog",
> >> @@ -148,6 +198,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >> struct watchdog_device *wdd;
> >> struct rti_wdt_device *wdt;
> >> struct clk *clk;
> >> + u32 last_ping = 0;
> >>
> >> wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
> >> if (!wdt)
> >> @@ -169,6 +220,14 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >> return -EINVAL;
> >> }
> >>
> >> + /*
> >> + * If watchdog is running at 32k clock, it is not accurate.
> >> + * Adjust frequency down in this case so that we don't pet
> >> + * the watchdog too often.
> >> + */
> >> + if (wdt->freq < 32768)
> >> + wdt->freq = wdt->freq * 9 / 10;
> >> +
> >
> > This seems broken: You are only adjusting the frequency value used by
> > the driver. What has been programmed into the hardware already is still
> > based on real frequency. Moreover, this path is not only taken when the
> > watchdog is already running - but the latter case is what the subject
> > and commit message suggests. I've noticed this by comparing
> > bootloader-programmed values with those the driver assumes to see - 10%
> > off, obviously.
> >
> > So, what is actually supposed to happen here?
This assumes that the clk is coming in from RC_OSC_32k - which is in the
range of accuracy of 10-20% off clock. also one more variable to keep in
mind is that the 32k divided clk from hfosc will not be exact.
Hari: Thoughts?
> >
> > Jan
> >
> >> pm_runtime_enable(dev);
> >> ret = pm_runtime_get_sync(dev);
> >> if (ret) {
> >> @@ -185,11 +244,8 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >> wdd->min_timeout = 1;
> >> wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
> >> wdt->freq * 1000;
> >> - wdd->timeout = DEFAULT_HEARTBEAT;
> >> wdd->parent = dev;
> >>
> >> - watchdog_init_timeout(wdd, heartbeat, dev);
> >> -
> >> watchdog_set_drvdata(wdd, wdt);
> >> watchdog_set_nowayout(wdd, 1);
> >> watchdog_set_restart_priority(wdd, 128);
> >> @@ -201,12 +257,48 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >> goto err_iomap;
> >> }
> >>
> >> + if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
> >> + u32 time_left_ms;
> >> + u64 heartbeat_ms;
> >> + u32 wsize;
> >> +
> >> + set_bit(WDOG_HW_RUNNING, &wdd->status);
> >> + time_left_ms = rti_wdt_get_timeleft_ms(wdd);
> >> + heartbeat_ms = readl(wdt->base + RTIDWDPRLD);
> >> + heartbeat_ms <<= WDT_PRELOAD_SHIFT;
> >> + heartbeat_ms *= 1000;
> >> + do_div(heartbeat_ms, wdt->freq);
> >> + if (heartbeat_ms != heartbeat * 1000)
> >> + dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
> >> +
> >> + heartbeat = heartbeat_ms;
> >> + heartbeat /= 1000;
> >> +
> >> + wsize = readl(wdt->base + RTIWWDSIZECTRL);
> >> + ret = rti_wdt_setup_hw_hb(wdd, wsize);
> >> + if (ret) {
> >> + dev_err(dev, "bad window size.\n");
> >> + goto err_iomap;
> >> + }
> >> +
> >> + last_ping = heartbeat_ms - time_left_ms;
> >> + if (time_left_ms > heartbeat_ms) {
> >> + dev_warn(dev, "time_left > heartbeat? Assuming last ping just before now.\n");
> >> + last_ping = 0;
> >> + }
> >> + }
> >> +
> >> + watchdog_init_timeout(wdd, heartbeat, dev);
> >> +
> >> ret = watchdog_register_device(wdd);
> >> if (ret) {
> >> dev_err(dev, "cannot register watchdog device\n");
> >> goto err_iomap;
> >> }
> >>
> >> + if (last_ping)
> >> + watchdog_set_last_hw_keepalive(wdd, last_ping);
> >> +
> >> return 0;
> >>
> >> err_iomap:
> >
>
> There is actually more "inaccurate". For now, I would try to address it
> like this:
>
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 88815419ad1a..1b6629fa5bfc 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -231,14 +231,6 @@ static int rti_wdt_probe(struct platform_device *pdev)
> return -EINVAL;
> }
>
> - /*
> - * If watchdog is running at 32k clock, it is not accurate.
> - * Adjust frequency down in this case so that we don't pet
> - * the watchdog too often.
> - */
> - if (wdt->freq < 32768)
> - wdt->freq = wdt->freq * 9 / 10;
> -
> pm_runtime_enable(dev);
> ret = pm_runtime_get_sync(dev);
> if (ret) {
> @@ -252,8 +244,6 @@ static int rti_wdt_probe(struct platform_device *pdev)
> wdd->info = &rti_wdt_info;
> wdd->ops = &rti_wdt_ops;
> wdd->min_timeout = 1;
> - wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
> - wdt->freq * 1000;
> wdd->parent = dev;
>
> watchdog_set_drvdata(wdd, wdt);
> @@ -280,7 +270,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
> if (heartbeat_ms != heartbeat * 1000)
> dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
>
> - heartbeat = heartbeat_ms;
> + heartbeat = heartbeat_ms + 500;
> heartbeat /= 1000;
>
> wsize = readl(wdt->base + RTIWWDSIZECTRL);
> @@ -297,6 +287,17 @@ static int rti_wdt_probe(struct platform_device *pdev)
> }
> }
>
> + /*
> + * If watchdog is running at 32k clock, it is not accurate.
> + * Adjust frequency down in this case so that we don't pet
> + * the watchdog too often.
> + */
> + if (wdt->freq < 32768)
> + wdt->freq = wdt->freq * 9 / 10;
> +
> + wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
> + wdt->freq * 1000;
> +
> watchdog_init_timeout(wdd, heartbeat, dev);
>
> ret = watchdog_register_device(wdd);
>
>
> This moves the virtual frequency tweaking after reading back the
> programmed timeout. It also properly rounds that up to full seconds so
> that, e.g., bootloader-programmed programmed 60s will become 59s in the
> driver. That could have led to too short min_hw_heartbeat_ms.
>
> I can send this out as real patch, but I'd still like to understand the
> freq fiddling first. Is that addressing a real hardware issue? Or was it
> actually papering over that round-up problem?
>
> Jan
>
> --
> Siemens AG, Technology
> Competence Center Embedded Linux
--
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D)/Fingerprint: F8A2 8693 54EB 8232 17A3 1A34 DDB5 849D 1736 249D
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