Message-ID: <1c403426-90c9-5478-4cba-852be5d5141b@roeck-us.net>
Date:   Fri, 10 Apr 2020 18:15:30 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sergey Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] watchdog: dw_wdt: Support devices with non-fixed TOP
 values

On 4/10/20 12:45 PM, Sergey Semin wrote:
> On Fri, Apr 10, 2020 at 09:21:35AM -0700, Guenter Roeck wrote:
>> On 4/10/20 5:59 AM, Sergey Semin wrote:
>>> On Sun, Mar 15, 2020 at 07:12:38AM -0700, Guenter Roeck wrote:
>>>> On Fri, Mar 06, 2020 at 04:27:44PM +0300, Sergey.Semin@...kalelectronics.ru wrote:
>>>>> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
>>>>>
>>>>> In case if the DW Watchdog IP core is synthesised with
>>>>> WDT_USE_FIX_TOP == false, the TOP interval indexes make the device
>>>>> to load a custom periods to the counter. These periods are hardwired
>>>>> at the synthesis stage and can be within [2^8, 2^(WDT_CNT_WIDTH - 1)].
>>>>> Alas their values can't be detected at runtime and must be somehow
>>>>> supplied to the driver so one could properly determine the watchdog
>>>>> timeout intervals. For this purpose we suggest to have a vendor-
>>>>> specific dts property "snps,watchdog-tops" utilized, which would
>>>>> provide an array of sixteen counter values. At device probe stage they
>>>>> will be used to initialize the watchdog device timeouts determined
>>>>> from the array values and current clocks source rate.
>>>>>
>>>>> In order to have custom TOP values supported the driver must be
>>>>> altered in the following way. First of all the fixed-top values
>>>>> ready-to-use array must be determined for compatibility with currently
>>>>> supported devices, which were synthesised with WDT_USE_FIX_TOP == true.
>>>>> Secondly we must redefine the timer period search functions. For
>>>>> generality they are redesigned in a way to support the TOP array with
>>>>> no limitations on the items order or value. Finally an array with
>>>>> pre-defined timeouts must be calculated at probe stage from either
>>>>> the custom or fixed TOP values depending on the DW watchdog component
>>>>> parameter WDT_USE_FIX_TOP value.
>>>>>
>>>>> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
>>>>> Signed-off-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
>>>>> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
>>>>> Cc: Paul Burton <paulburton@...nel.org>
>>>>> Cc: Ralf Baechle <ralf@...ux-mips.org>
>>>>> ---
>>>>>  drivers/watchdog/dw_wdt.c | 145 +++++++++++++++++++++++++++++++-------
>>>>>  1 file changed, 119 insertions(+), 26 deletions(-)
>>>>>
>>>>> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
>>>>> index fba21de2bbad..4a57b7d777dc 100644
>>>>> --- a/drivers/watchdog/dw_wdt.c
>>>>> +++ b/drivers/watchdog/dw_wdt.c
>>>>> @@ -13,6 +13,7 @@
>>>>>   */
>>>>>  
>>>>>  #include <linux/bitops.h>
>>>>> +#include <linux/limits.h>
>>>>>  #include <linux/clk.h>
>>>>>  #include <linux/delay.h>
>>>>>  #include <linux/err.h>
>>>>> @@ -34,12 +35,24 @@
>>>>>  #define WDOG_CURRENT_COUNT_REG_OFFSET	    0x08
>>>>>  #define WDOG_COUNTER_RESTART_REG_OFFSET     0x0c
>>>>>  #define WDOG_COUNTER_RESTART_KICK_VALUE	    0x76
>>>>> +#define WDOG_COMP_PARAMS_1_REG_OFFSET       0xf4
>>>>> +#define WDOG_COMP_PARAMS_1_USE_FIX_TOP      BIT(6)
>>>>>  
>>>>> -/* The maximum TOP (timeout period) value that can be set in the watchdog. */
>>>>> -#define DW_WDT_MAX_TOP		15
>>>>> +/* There are sixteen TOPs (timeout periods) that can be set in the watchdog. */
>>>>> +#define DW_WDT_NUM_TOPS		16
>>>>> +#define DW_WDT_FIX_TOP(_idx)	(1U << (16 + _idx))
>>>>>  
>>>>>  #define DW_WDT_DEFAULT_SECONDS	30
>>>>>  
>>>>> +static const u32 dw_wdt_fix_tops[DW_WDT_NUM_TOPS] = {
>>>>> +	DW_WDT_FIX_TOP(0), DW_WDT_FIX_TOP(1), DW_WDT_FIX_TOP(2),
>>>>> +	DW_WDT_FIX_TOP(3), DW_WDT_FIX_TOP(4), DW_WDT_FIX_TOP(5),
>>>>> +	DW_WDT_FIX_TOP(6), DW_WDT_FIX_TOP(7), DW_WDT_FIX_TOP(8),
>>>>> +	DW_WDT_FIX_TOP(9), DW_WDT_FIX_TOP(10), DW_WDT_FIX_TOP(11),
>>>>> +	DW_WDT_FIX_TOP(12), DW_WDT_FIX_TOP(13), DW_WDT_FIX_TOP(14),
>>>>> +	DW_WDT_FIX_TOP(15)
>>>>> +};
>>>>> +
>>>>>  static bool nowayout = WATCHDOG_NOWAYOUT;
>>>>>  module_param(nowayout, bool, 0);
>>>>>  MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
>>>>> @@ -49,6 +62,8 @@ struct dw_wdt {
>>>>>  	void __iomem		*regs;
>>>>>  	struct clk		*clk;
>>>>>  	unsigned long		rate;
>>>>> +	unsigned int		max_top;
>>>>> +	unsigned int		timeouts[DW_WDT_NUM_TOPS];
>>>>>  	struct watchdog_device	wdd;
>>>>>  	struct reset_control	*rst;
>>>>>  	/* Save/restore */
>>>>> @@ -64,20 +79,68 @@ static inline int dw_wdt_is_enabled(struct dw_wdt *dw_wdt)
>>>>>  		WDOG_CONTROL_REG_WDT_EN_MASK;
>>>>>  }
>>>>>  
>>>>> -static inline int dw_wdt_top_in_seconds(struct dw_wdt *dw_wdt, unsigned top)
>>>>> +static unsigned int dw_wdt_find_best_top(struct dw_wdt *dw_wdt,
>>>>> +					 unsigned int timeout, u32 *top)
>>>>>  {
>>>>> +	u32 diff = UINT_MAX, tmp;
>>>>> +	int idx;
>>>>> +
>>>>>  	/*
>>>>> -	 * There are 16 possible timeout values in 0..15 where the number of
>>>>> -	 * cycles is 2 ^ (16 + i) and the watchdog counts down.
>>>>> +	 * In general case of non-fixed timeout values they can be arranged in
>>>>> +	 * any order so we have to traverse all the array values. We also try
>>>>> +	 * to find a closest timeout number and make sure its value is greater
>>>>> +	 * than the requested timeout. Note we'll return a maximum timeout
>>>>> +	 * if reachable value couldn't be found.
>>>>>  	 */
>>>>> -	return (1U << (16 + top)) / dw_wdt->rate;
>>>>> +	for (*top = dw_wdt->max_top, idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
>>>>> +		if (dw_wdt->timeouts[idx] < timeout)
>>>>> +			continue;
>>>>> +
>>>>> +		tmp = dw_wdt->timeouts[idx] - timeout;
>>>>> +		if (tmp < diff) {
>>>>> +			diff = tmp;
>>>>> +			*top = idx;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	return dw_wdt->timeouts[*top];
>>>>> +}
>>>>> +
>>>>> +static unsigned int dw_wdt_find_min_timeout(struct dw_wdt *dw_wdt)
>>>>
>>>> I would appreciate if the names of functions returning ms end with _ms
>>>> to avoid confusion.
>>>
>>> Ok. I'll also modify the functions a bit, so only the
>>> dw_wdt_find_best_top_ms() and dw_wdt_find_max_top_ms() methods would
>>> return timeouts in milliseconds. Though if you insist in keeping seconds
>>> in the timeouts array (see the comment after the next one), it'll be
>>> dw_wdt_find_max_top_ms() only.
>>>
>>>>
>>>>> +{
>>>>> +	u32 min_timeout = UINT_MAX, top;
>>>>> +	int idx;
>>>>> +
>>>>> +	for (top = 0, idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
>>>>> +		if (dw_wdt->timeouts[idx] <= min_timeout) {
>>>>> +			min_timeout = dw_wdt->timeouts[idx];
>>>>> +			top = idx;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	return dw_wdt->timeouts[top];
>>>>> +}
>>>>> +
>>>>> +static unsigned int dw_wdt_find_max_top(struct dw_wdt *dw_wdt, u32 *top)
>>>>> +{
>>>>> +	u32 max_timeout = 0;
>>>>> +	int idx;
>>>>> +
>>>>> +	for (*top = 0, idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
>>>>> +		if (dw_wdt->timeouts[idx] >= max_timeout) {
>>>>> +			max_timeout = dw_wdt->timeouts[idx];
>>>>> +			*top = idx;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	return dw_wdt->timeouts[*top];
>>>>>  }
>>>>>  
>>>>> -static int dw_wdt_get_top(struct dw_wdt *dw_wdt)
>>>>> +static unsigned int dw_wdt_get_timeout(struct dw_wdt *dw_wdt)
>>>>>  {
>>>>>  	int top = readl(dw_wdt->regs + WDOG_TIMEOUT_RANGE_REG_OFFSET) & 0xF;
>>>>>  
>>>>> -	return dw_wdt_top_in_seconds(dw_wdt, top);
>>>>> +	return dw_wdt->timeouts[top];
>>>>>  }
>>>>>  
>>>>>  static int dw_wdt_ping(struct watchdog_device *wdd)
>>>>> @@ -90,20 +153,13 @@ static int dw_wdt_ping(struct watchdog_device *wdd)
>>>>>  	return 0;
>>>>>  }
>>>>>  
>>>>> -static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
>>>>> +static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int req)
>>>>>  {
>>>>>  	struct dw_wdt *dw_wdt = to_dw_wdt(wdd);
>>>>> -	int i, top_val = DW_WDT_MAX_TOP;
>>>>> +	unsigned int timeout;
>>>>> +	u32 top;
>>>>>  
>>>>> -	/*
>>>>> -	 * Iterate over the timeout values until we find the closest match. We
>>>>> -	 * always look for >=.
>>>>> -	 */
>>>>> -	for (i = 0; i <= DW_WDT_MAX_TOP; ++i)
>>>>> -		if (dw_wdt_top_in_seconds(dw_wdt, i) >= top_s) {
>>>>> -			top_val = i;
>>>>> -			break;
>>>>> -		}
>>>>> +	timeout = dw_wdt_find_best_top(dw_wdt, req * MSEC_PER_SEC, &top);
>>>>>  
>>>>>  	/*
>>>>>  	 * Set the new value in the watchdog.  Some versions of dw_wdt
>>>>> @@ -111,7 +167,7 @@ static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
>>>>>  	 * CP_WDT_DUAL_TOP in WDT_COMP_PARAMS_1).  On those we
>>>>>  	 * effectively get a pat of the watchdog right here.
>>>>>  	 */
>>>>> -	writel(top_val | top_val << WDOG_TIMEOUT_RANGE_TOPINIT_SHIFT,
>>>>> +	writel(top | top << WDOG_TIMEOUT_RANGE_TOPINIT_SHIFT,
>>>>>  	       dw_wdt->regs + WDOG_TIMEOUT_RANGE_REG_OFFSET);
>>>>>  
>>>>>  	/*
>>>>> @@ -119,10 +175,10 @@ static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
>>>>>  	 * kernel(watchdog_dev.c) helps to feed watchdog before
>>>>>  	 * wdd->max_hw_heartbeat_ms
>>>>>  	 */
>>>>> -	if (top_s * 1000 <= wdd->max_hw_heartbeat_ms)
>>>>> -		wdd->timeout = dw_wdt_top_in_seconds(dw_wdt, top_val);
>>>>> +	if (req * MSEC_PER_SEC > wdd->max_hw_heartbeat_ms)
>>>>> +		wdd->timeout = req;
>>>>>  	else
>>>>> -		wdd->timeout = top_s;
>>>>> +		wdd->timeout = timeout / MSEC_PER_SEC;
>>>>>  
>>>>>  	return 0;
>>>>>  }
>>>>> @@ -238,6 +294,41 @@ static int dw_wdt_resume(struct device *dev)
>>>>>  
>>>>>  static SIMPLE_DEV_PM_OPS(dw_wdt_pm_ops, dw_wdt_suspend, dw_wdt_resume);
>>>>>  
>>>>> +static void dw_wdt_init_timeouts(struct dw_wdt *dw_wdt, struct device *dev)
>>>>> +{
>>>>> +	u32 data, of_tops[DW_WDT_NUM_TOPS];
>>>>> +	const u32 *tops;
>>>>> +	int ret, idx;
>>>>> +
>>>>> +	/*
>>>>> +	 * Retrieve custom or fixed counter values depending on the
>>>>> +	 * WDT_USE_FIX_TOP flag found in the component specific parameters
>>>>> +	 * #1 register.
>>>>> +	 */
>>>>> +	data = readl(dw_wdt->regs + WDOG_COMP_PARAMS_1_REG_OFFSET);
>>>>> +	if (data & WDOG_COMP_PARAMS_1_USE_FIX_TOP) {
>>>>> +		tops = dw_wdt_fix_tops;
>>>>> +	} else {
>>>>> +		ret = of_property_read_variable_u32_array(dev_of_node(dev),
>>>>> +			"snps,watchdog-tops", of_tops, DW_WDT_NUM_TOPS,
>>>>> +			DW_WDT_NUM_TOPS);
>>>>> +		if (ret < 0) {
>>>>> +			dev_warn(dev, "No valid TOPs array specified\n");
>>>>> +			tops = dw_wdt_fix_tops;
>>>>> +		} else {
>>>>> +			tops = of_tops;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	/*
>>>>> +	 * We'll keep the timeout values in ms to approximate requested
>>>>> +	 * timeouts with better accuracy.
>>>>> +	 */
>>>>> +	for (idx = 0; idx < DW_WDT_NUM_TOPS; ++idx)
>>>>> +		dw_wdt->timeouts[idx] =
>>>>> +			mult_frac(tops[idx], MSEC_PER_SEC, dw_wdt->rate);
>>>>
>>>> tops[idx] type is u32. Its value can be up to 0xffffffff. That means
>>>> dw_wdt->rate must be >= 1000 to avoid overflow, which you should check.
>>>
>>> Right. I don't think that TOPs with timeouts bigger than
>>> 0xffffffff milliseconds have any valuable usecases, so I'll just round
>>> the overflows down to FFs.
>>>
>>
>> Neither do unsorted random timeouts milli-seconds apart. You see the need
>> to address one, so addressing other weaknesses is appropriate.
> 
> Don't really understand what you mean. Do you intend to filter the
> unreachable timeouts out from the timeouts array? If so this isn't
> possible with current design. I would have to implement a more complex
> data structure, like an array of pairs {TOP, timeout} and refactor the
> timeout search algorithm. Don't really think this optimization is required
> seeing watchdog timeout set operation is normally performed just a few times
> per watchdog usage session.
> 

You state that defining a tops[idx] value > 0xffffffff / 1000 would be
unreasonable, while at the same time you argue that a sequence of tops[idx]
values of, say, 45, 46, 47, 43, 42, 99, 98, 55 would be perfectly reasonable
and needs to be handled. All I am saying is that you need to deal with all odd
cases, and that you can not assume that there is no tops[idx] value that results
in an overflow. If "45, 46, 47, 43, 42, 99, 98, 55" is reasonable, so is
0xffffffff.

Guenter

Powered by blists - more mailing lists