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Message-ID: <bdecc38d-2b1a-9605-0978-5ad1e8b39e6b@siemens.com>
Date: Mon, 21 Feb 2022 10:59:20 +0100
From: Jan Kiszka <jan.kiszka@...mens.com>
To: <wim@...ux-watchdog.org>, <linux@...ck-us.net>,
<linux-watchdog@...r.kernel.org>, Nishanth Menon <nm@...com>
CC: <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv4 3/4] watchdog: rti-wdt: attach to running watchdog
during probe
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?
>
> 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
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