RE: [PATCH v4 2/2] watchdog: Add Watchdog Timer driver for RZ/G2L

[Biju Das <biju.das.jz@bp.renesas.com>]

> Subject: RE: [PATCH v4 2/2] watchdog: Add Watchdog Timer driver for RZ/G2L
> 
> Hi Guenter,
> 
> Thanks for the feedback.
> 
> > Subject: Re: [PATCH v4 2/2] watchdog: Add Watchdog Timer driver for
> > RZ/G2L
> >
> > On 11/30/21 3:43 AM, Biju Das wrote:
> > > Add Watchdog Timer driver for RZ/G2L SoC.
> > >
> > > WDT IP block supports normal watchdog timer function and reset
> > > request function due to CPU parity error.
> > >
> > > This driver currently supports normal watchdog timer function and
> > > later will add support for reset request function due to CPU parity
> > > error.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> > > ---
> > > V3->V4:
> > >   * Fixed the build issue reported by kernel test robot by Replacing
> the
> > >     macro WDT_CYCLE_MSEC with div64_ul for 64-bit division to fix 32-
> bit
> > >     kernels.
> > > V2->V3:
> > >   * Added Rb tag from Guenter Roeck
> > > V1->V2:
> > >   * started using clk_get/put instead of devm_clk_get/put
> > >   * Moved devm_add_action_or_reset after set_drvdata() and
> > >   * removed redundant action on devm_add_action_or_reset() failure.
> > > RFC->V1
> > >   * Removed pclk_rate from priv.
> > >   * rzg2l_wdt_write() returns void and Removed tiemout related to
> > register update
> > >   * rzg2l_wdt_init_timeout() returns void and removed delays.
> > >   * removed set_bit(WDOG_HW_RUNNING,..) as we can stop watchdog
> > >   * renamed reset_assert_clock_disable->reset_assert_pm_disable_put
> > >   * started using devm_reset_control_get_exclusive()
> > >   * removed platform_set_drvdata(pdev, priv) as there is no user
> > >   * removed watchdog_set_restart_priority(&priv->wdev, 0) as 0 is
> > > the
> > default.
> > >   * removed remove callback as it is empty.
> > > ---
> > >   drivers/watchdog/Kconfig     |   8 ++
> > >   drivers/watchdog/Makefile    |   1 +
> > >   drivers/watchdog/rzg2l_wdt.c | 260
> +++++++++++++++++++++++++++++++++++
> > >   3 files changed, 269 insertions(+)
> > >   create mode 100644 drivers/watchdog/rzg2l_wdt.c
> > >
> > > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> > > index
> > > 9d222ba17ec6..4760ee981263 100644
> > > --- a/drivers/watchdog/Kconfig
> > > +++ b/drivers/watchdog/Kconfig
> > > @@ -881,6 +881,14 @@ config RENESAS_RZAWDT
> > >   	  This driver adds watchdog support for the integrated
> watchdogs
> > > in
> > the
> > >   	  Renesas RZ/A SoCs. These watchdogs can be used to reset a
> system.
> > >
> > > +config RENESAS_RZG2LWDT
> > > +	tristate "Renesas RZ/G2L WDT Watchdog"
> > > +	depends on ARCH_RENESAS || COMPILE_TEST
> > > +	select WATCHDOG_CORE
> > > +	help
> > > +	  This driver adds watchdog support for the integrated watchdogs
> > > +in
> > the
> > > +	  Renesas RZ/G2L SoCs. These watchdogs can be used to reset a
> > system.
> > > +
> > >   config ASPEED_WATCHDOG
> > >   	tristate "Aspeed BMC watchdog support"
> > >   	depends on ARCH_ASPEED || COMPILE_TEST diff --git
> > > a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile index
> > > 2ee97064145b..9a3dc0bd271b 100644
> > > --- a/drivers/watchdog/Makefile
> > > +++ b/drivers/watchdog/Makefile
> > > @@ -84,6 +84,7 @@ obj-$(CONFIG_LPC18XX_WATCHDOG) += lpc18xx_wdt.o
> > >   obj-$(CONFIG_BCM7038_WDT) += bcm7038_wdt.o
> > >   obj-$(CONFIG_RENESAS_WDT) += renesas_wdt.o
> > >   obj-$(CONFIG_RENESAS_RZAWDT) += rza_wdt.o
> > > +obj-$(CONFIG_RENESAS_RZG2LWDT) += rzg2l_wdt.o
> > >   obj-$(CONFIG_ASPEED_WATCHDOG) += aspeed_wdt.o
> > >   obj-$(CONFIG_STM32_WATCHDOG) += stm32_iwdg.o
> > >   obj-$(CONFIG_UNIPHIER_WATCHDOG) += uniphier_wdt.o diff --git
> > > a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c new
> > > file mode 100644 index 000000000000..69530b92fff9
> > > --- /dev/null
> > > +++ b/drivers/watchdog/rzg2l_wdt.c
> > > @@ -0,0 +1,260 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Renesas RZ/G2L WDT Watchdog Driver
> > > + *
> > > + * Copyright (C) 2021 Renesas Electronics Corporation  */ #include
> > > +<linux/bitops.h> #include <linux/clk.h> #include <linux/delay.h>
> > > +#include <linux/io.h> #include <linux/kernel.h> #include
> > > +<linux/module.h> #include <linux/of.h> #include
> > > +<linux/platform_device.h> #include <linux/pm_runtime.h> #include
> > > +<linux/reset.h> #include <linux/watchdog.h>
> > > +
> > > +#define WDTCNT		0x00
> > > +#define WDTSET		0x04
> > > +#define WDTTIM		0x08
> > > +#define WDTINT		0x0C
> > > +#define WDTCNT_WDTEN	BIT(0)
> > > +#define WDTINT_INTDISP	BIT(0)
> > > +
> > > +#define WDT_DEFAULT_TIMEOUT		60U
> > > +
> > > +/* Setting period time register only 12 bit set in WDTSET[31:20] */
> > > +#define WDTSET_COUNTER_MASK		(0xFFF00000)
> > > +#define WDTSET_COUNTER_VAL(f)		((f) << 20)
> > > +
> > > +#define F2CYCLE_NSEC(f)			(1000000000 / (f))
> > > +
> > > +static bool nowayout = WATCHDOG_NOWAYOUT; module_param(nowayout,
> > > +bool, 0); MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped
> > > +once started (default="
> > > +				__MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
> > > +
> > > +struct rzg2l_wdt_priv {
> > > +	void __iomem *base;
> > > +	struct watchdog_device wdev;
> > > +	struct reset_control *rstc;
> > > +	unsigned long osc_clk_rate;
> > > +	unsigned long delay;
> > > +};
> > > +
> > > +static void rzg2l_wdt_wait_delay(struct rzg2l_wdt_priv *priv) {
> > > +	/* delay timer when change the setting register */
> > > +	ndelay(priv->delay);
> > > +}
> > > +
> > > +static u32 rzg2l_wdt_get_cycle_msec(unsigned long cycle, u32
> > > +wdttime) {
> > > +	u64 timer_cycle_ms = 1024 * 1024 * 1000000ULL * (wdttime + 1);
> > > +
> > > +	return div64_ul(timer_cycle_ms, cycle); }
> >
> > A description might be warranted here. The return value appears to be
> > a timeout in seconds, based on
> > 	priv->wdev.max_timeout = rzg2l_wdt_get_cycle_msec(priv-
> > >osc_clk_rate, 0xfff); but that is not what the function name suggests.
> >
> > Also, the maximum timeouts seem to be excessive. Feeding the above
> > function into test code, I get
> >
> 
> As per HW manual,
> 24MHz is our SoC input clock,
> 
> Equation is 1024 *1024 * (t +1)  /(24 * 100000) seconds.
> 
> Min value of 0 corresponds to .4369sec, if you convert it into
> microseconds it becomes 0.43690x1000000 = 436906 microseconds
> 
> Max value of 0xfff corresponds to 1789956.97 msec, if you convert it into
> microseconds it becomes 1789956970 = 0x6AB0936A , I agree it is a big
> value, but it is with in 32bit limits.
> 
> > clk: 10000000 max timeout: 429496729
> > clk: 20000000 max timeout: 214748364
> > clk: 40000000 max timeout: 107374182
> > clk: 80000000 max timeout: 53687091
> > clk: 160000000 max timeout: 26843545
> > clk: 320000000 max timeout: 13421772
> > clk: 640000000 max timeout: 6710886
> > clk: 1280000000 max timeout: 3355443
> >
> > That really doesn't look correct. Even in milli-seconds, a maximum
> > timeout of 429496729 ms or 429496.729 seconds at 10 MHz clock rate seems
> high.
> >
> > > +
> > > +static void rzg2l_wdt_write(struct rzg2l_wdt_priv *priv, u32 val,
> > > +unsigned int reg) {
> > > +	if (reg == WDTSET)
> > > +		val &= WDTSET_COUNTER_MASK;
> > > +
> > > +	writel_relaxed(val, priv->base + reg);
> > > +	/* Registers other than the WDTINT is always synchronized with
> > WDT_CLK */
> > > +	if (reg != WDTINT)
> > > +		rzg2l_wdt_wait_delay(priv);
> > > +}
> > > +
> > > +static void rzg2l_wdt_init_timeout(struct watchdog_device *wdev) {
> > > +	struct rzg2l_wdt_priv *priv = watchdog_get_drvdata(wdev);
> > > +	u32 time_out;
> > > +
> > > +	/* Clear Lapsed Time Register and clear Interrupt */
> > > +	rzg2l_wdt_write(priv, WDTINT_INTDISP, WDTINT);
> > > +	/* 2 consecutive overflow cycle needed to trigger reset */
> > > +	time_out = (wdev->timeout / 2 * 1000000) /
> > > +rzg2l_wdt_get_cycle_msec(priv->osc_clk_rate, 0);
> >
> > This code effectively reduces timer granularity to 2 seconds. Is that
> > on purpose ?
> 
> Yes, it needs 2 consecutive overflow cycle for triggering watchdog reset
> 
> As per the above calculation,
> 
> 60 secs Default timeout, the counter value = 30000000 microsec/436906
> microsec = 686
> 
> And it triggers watchdog around 60 sec with the command cat /dev/watchdog
> & for i in {1..60}; do sleep 1; echo $i; devmem2 0x12800808; done
> 
> > Why not something like
> > 	time_out = (wdev->timeout * (1000000 / 2)) /
> > rzg2l_wdt_get_cycle_msec(priv->osc_clk_rate, 0); instead ?
> 
> 
> Ok.
> 
> >
> > Also, feeding the maximum timeout as calculated by
> > rzg2l_wdt_get_cycle_msec(priv->osc_clk_rate, 0xfff) into this
> > expression yields really large numbers. Making things worse, those
> > long timeouts cause
> > 	wdev->timeout / 2 * 1000000
> > to overflow easily. This calculation alone suggests that the maximum
> > timeout value can not be larger than ~8589 to avoid that overflow.
> >
> > More test code gives me:
> >
> > clk: 10000000 max timeout: 429496729
> >    timeout: 1s reg: 0x0
> >    timeout: 2s reg: 0x9
> >    timeout: 859s reg: 0xffb
> >      Overflow: t=214748364 treg: 0x3d0916df
> >    timeout: 214748364s reg: 0xffffffff
> >      Overflow: t=429496729 treg: 0x7a122dbf
> >    timeout: 429496729s reg: 0xffffffff
> >
> > clk: 320000000 max timeout: 13421772
> >    timeout: 1s reg: 0x0
> >    timeout: 2s reg: 0x131
> >    timeout: 27s reg: 0xf80
> >      Overflow: t=6710886 treg: 0x3d0cd090
> >    timeout: 6710886s reg: 0xffffffff
> >      Overflow: t=13421772 treg: 0x7a19a120
> >    timeout: 13421772s reg: 0xffffffff
> >
> > and similar for other clock rates. This shows both the impact of the
> > artificial 2s granularity and the value overflows.
> >
> > Something in the calculation of max_timeout or in the calculation of
> > the register value or both is wrong. Whatever it is, it needs to get
> fixed.

Yes, you are right, calculation of max_timeout is wrong. Currently it is microseconds
Needs to convert it into seconds.

Cheers,
Biju