Re: [PATCH 7/7] watchdog: dw_wdt: Add DebugFS files

[Sergey Semin <Sergey.Semin@baikalelectronics.ru>]

On Fri, Mar 06, 2020 at 07:12:32AM -0800, Guenter Roeck wrote:
> On 3/6/20 5:27 AM, Sergey.Semin@baikalelectronics.ru wrote:
> > From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > 
> > For the sake of the easier device-driver debug procedure, we added a
> > few DebugFS files with the next content: watchdog timeout, watchdog
> > pre-timeout, watchdog ping/kick operation, watchdog start/stop, device
> > registers dump. They are available only if kernel is configured with
> > DebugFS support.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > Signed-off-by: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Paul Burton <paulburton@kernel.org>
> > Cc: Ralf Baechle <ralf@linux-mips.org>
> > ---
> >  drivers/watchdog/dw_wdt.c | 150 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 150 insertions(+)
> > 
> > diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> > index 3000120f7e39..9353d83f3e45 100644
> > --- a/drivers/watchdog/dw_wdt.c
> > +++ b/drivers/watchdog/dw_wdt.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/platform_device.h>
> >  #include <linux/reset.h>
> >  #include <linux/watchdog.h>
> > +#include <linux/debugfs.h>
> >  
> >  #define WDOG_CONTROL_REG_OFFSET		    0x00
> >  #define WDOG_CONTROL_REG_WDT_EN_MASK	    0x01
> > @@ -38,8 +39,14 @@
> >  #define WDOG_COUNTER_RESTART_KICK_VALUE	    0x76
> >  #define WDOG_INTERRUPT_STATUS_REG_OFFSET    0x10
> >  #define WDOG_INTERRUPT_CLEAR_REG_OFFSET     0x14
> > +#define WDOG_COMP_PARAMS_5_REG_OFFSET       0xe4
> > +#define WDOG_COMP_PARAMS_4_REG_OFFSET       0xe8
> > +#define WDOG_COMP_PARAMS_3_REG_OFFSET       0xec
> > +#define WDOG_COMP_PARAMS_2_REG_OFFSET       0xf0
> >  #define WDOG_COMP_PARAMS_1_REG_OFFSET       0xf4
> >  #define WDOG_COMP_PARAMS_1_USE_FIX_TOP      BIT(6)
> > +#define WDOG_COMP_VERSION_REG_OFFSET        0xf8
> > +#define WDOG_COMP_TYPE_REG_OFFSET           0xfc
> >  
> >  /* There are sixteen TOPs (timeout periods) that can be set in the watchdog. */
> >  #define DW_WDT_NUM_TOPS		16
> > @@ -79,6 +86,10 @@ struct dw_wdt {
> >  	/* Save/restore */
> >  	u32			control;
> >  	u32			timeout;
> > +
> > +#ifdef CONFIG_DEBUG_FS
> > +	struct dentry		*dbgfs_dir;
> > +#endif
> >  };
> >  
> >  #define to_dw_wdt(wdd)	container_of(wdd, struct dw_wdt, wdd)
> > @@ -430,6 +441,141 @@ static void dw_wdt_init_timeouts(struct dw_wdt *dw_wdt, struct device *dev)
> >  			mult_frac(tops[idx], MSEC_PER_SEC, dw_wdt->rate);
> >  }
> >  
> > +#ifdef CONFIG_DEBUG_FS
> > +
> > +static int dw_wdt_dbgfs_timeout_get(void *priv, u64 *val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	*val = dw_wdt_get_timeout(dw_wdt) / MSEC_PER_SEC;
> > +
> > +	return 0;
> > +}
> > +
> > +static int dw_wdt_dbgfs_timeout_set(void *priv, u64 val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	return dw_wdt_set_timeout(&dw_wdt->wdd, val);
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(dw_wdt_dbgfs_timeout_fops,
> > +	dw_wdt_dbgfs_timeout_get, dw_wdt_dbgfs_timeout_set, "%llu\n");
> > +
> > +static int dw_wdt_dbgfs_pretimeout_get(void *priv, u64 *val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	*val = dw_wdt->wdd.pretimeout;
> > +
> > +	return 0;
> > +}
> > +
> > +static int dw_wdt_dbgfs_pretimeout_set(void *priv, u64 val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	return dw_wdt_set_pretimeout(&dw_wdt->wdd, val);
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(dw_wdt_dbgfs_pretimeout_fops,
> > +	dw_wdt_dbgfs_pretimeout_get, dw_wdt_dbgfs_pretimeout_set, "%llu\n");
> > +
> > +static int dw_wdt_dbgfs_ping_set(void *priv, u64 val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	dw_wdt_ping(&dw_wdt->wdd);
> > +
> > +	return 0;
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(dw_wdt_dbgfs_ping_fops,
> > +	NULL, dw_wdt_dbgfs_ping_set, "%llu\n");
> > +
> > +static int dw_wdt_dbgfs_en_get(void *priv, u64 *val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	*val = !!dw_wdt_is_enabled(dw_wdt);
> > +
> > +	return 0;
> > +}
> > +
> > +static int dw_wdt_dbgfs_en_set(void *priv, u64 val)
> > +{
> > +	struct dw_wdt *dw_wdt = priv;
> > +
> > +	if (val)
> > +		dw_wdt_start(&dw_wdt->wdd);
> > +	else
> > +		dw_wdt_stop(&dw_wdt->wdd);
> > +
> > +	return 0;
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(dw_wdt_dbgfs_en_fops,
> > +	dw_wdt_dbgfs_en_get, dw_wdt_dbgfs_en_set, "%llu\n");
> > +
> > +#define DW_WDT_DBGFS_REG(_name, _off) \
> > +{				      \
> > +	.name = _name,		      \
> > +	.offset = _off		      \
> > +}
> > +
> > +static const struct debugfs_reg32 dw_wdt_dbgfs_regs[] = {
> > +	DW_WDT_DBGFS_REG("cr", WDOG_CONTROL_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("torr", WDOG_TIMEOUT_RANGE_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("ccvr", WDOG_CURRENT_COUNT_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("crr", WDOG_COUNTER_RESTART_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("stat", WDOG_INTERRUPT_STATUS_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("param5", WDOG_COMP_PARAMS_5_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("param4", WDOG_COMP_PARAMS_4_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("param3", WDOG_COMP_PARAMS_3_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("param2", WDOG_COMP_PARAMS_2_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("param1", WDOG_COMP_PARAMS_1_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("version", WDOG_COMP_VERSION_REG_OFFSET),
> > +	DW_WDT_DBGFS_REG("type", WDOG_COMP_TYPE_REG_OFFSET)
> > +};
> > +
> > +static void dw_wdt_dbgfs_init(struct dw_wdt *dw_wdt)
> > +{
> > +	struct device *dev = dw_wdt->wdd.parent;
> > +	struct debugfs_regset32 *regset;
> > +
> > +	regset = devm_kzalloc(dev, sizeof(*regset), GFP_KERNEL);
> > +	if (!regset)
> > +		return;
> > +
> > +	regset->regs = dw_wdt_dbgfs_regs;
> > +	regset->nregs = ARRAY_SIZE(dw_wdt_dbgfs_regs);
> > +	regset->base = dw_wdt->regs;
> > +
> > +	dw_wdt->dbgfs_dir = debugfs_create_dir(dev_name(dev), NULL);
> > +
> > +	debugfs_create_regset32("registers", 0444, dw_wdt->dbgfs_dir, regset);
> > +
> > +	debugfs_create_file_unsafe("timeout", 0600, dw_wdt->dbgfs_dir,
> > +				   dw_wdt, &dw_wdt_dbgfs_timeout_fops);
> > +
> > +	debugfs_create_file_unsafe("pretimeout", 0600, dw_wdt->dbgfs_dir,
> > +				   dw_wdt, &dw_wdt_dbgfs_pretimeout_fops);
> > +
> > +	debugfs_create_file_unsafe("ping", 0200, dw_wdt->dbgfs_dir,
> > +				   dw_wdt, &dw_wdt_dbgfs_ping_fops);
> > +
> > +	debugfs_create_file_unsafe("enable", 0600, dw_wdt->dbgfs_dir,
> > +				   dw_wdt, &dw_wdt_dbgfs_en_fops);
> > +}
> 
> I don't oppose debugfs support in general, but I really don't see
> the point replicating watchdog core functionality for it - even more so
> since this bypasses the watchdog core. This lets one, for example,
> enable the watchdog and then unload the driver with the watchdog
> running. This is not only unnecessary, it is way too dangerous,
> debugfs or not.
> 
> NACK for that part.

I see your point. What if I keep the registers dump and read-only
timeout, pretimeout, enable and timeleft nodes? This won't be harmful,
but the info still can be useful to debug the driver.

-Sergey

> 
> Guenter
> 
> > +
> > +static void dw_wdt_dbgfs_clear(struct dw_wdt *dw_wdt)
> > +{
> > +	debugfs_remove_recursive(dw_wdt->dbgfs_dir);
> > +}
> > +
> > +#else /* !CONFIG_DEBUG_FS */
> > +
> > +static void dw_wdt_dbgfs_init(struct dw_wdt *dw_wdt) {}
> > +static void dw_wdt_dbgfs_clear(struct dw_wdt *dw_wdt) {}
> > +
> > +#endif /* !CONFIG_DEBUG_FS */
> > +
> >  static int dw_wdt_drv_probe(struct platform_device *pdev)
> >  {
> >  	struct device *dev = &pdev->dev;
> > @@ -544,6 +690,8 @@ static int dw_wdt_drv_probe(struct platform_device *pdev)
> >  	if (ret)
> >  		goto out_disable_pclk;
> >  
> > +	dw_wdt_dbgfs_init(dw_wdt);
> > +
> >  	return 0;
> >  
> >  out_disable_pclk:
> > @@ -558,6 +706,8 @@ static int dw_wdt_drv_remove(struct platform_device *pdev)
> >  {
> >  	struct dw_wdt *dw_wdt = platform_get_drvdata(pdev);
> >  
> > +	dw_wdt_dbgfs_clear(dw_wdt);
> > +
> >  	watchdog_unregister_device(&dw_wdt->wdd);
> >  	reset_control_assert(dw_wdt->rst);
> >  	clk_disable_unprepare(dw_wdt->pclk);
> > 
>