Re: [PATCH v2 5/6] watchdog: Add Renesas RZ/N1 Watchdog driver

[Jean-Jacques Hiblot <jjhiblot@traphandler.com>]

Hi Geert,

On 09/02/2022 09:28, Geert Uytterhoeven wrote:
> Hi Jean-Jacques,
>
> On Tue, Feb 8, 2022 at 7:35 PM Jean-Jacques Hiblot
> <jjhiblot@traphandler.com> wrote:
>> From: Phil Edworthy <phil.edworthy@renesas.com>
>>
>> This is a driver for the standard WDT on the RZ/N1 devices. This WDT has
>> very limited timeout capabilities. However, it can reset the device.
>> To do so, the corresponding bits in the SysCtrl RSTEN register need to
>> be enabled. This is not done by this driver.
>>
>> Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
>> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
> Thanks for your patch!
>
>> --- /dev/null
>> +++ b/drivers/watchdog/rzn1_wdt.c
>> @@ -0,0 +1,208 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Renesas RZ/N1 Watchdog timer.
>> + * This is a 12-bit timer driver from a (62.5/16384) MHz clock. It can't even
>> + * cope with 2 seconds.
>> + *
>> + * Copyright 2018 Renesas Electronics Europe Ltd.
>> + *
>> + * Derived from Ralink RT288x watchdog timer.
>> + */
>> +
>> +#include <linux/clk.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/of_address.h>
>> +#include <linux/of_irq.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/watchdog.h>
>> +
>> +#define DEFAULT_TIMEOUT                60
>> +
>> +#define RZN1_WDT_RETRIGGER                     0x0
>> +#define RZN1_WDT_RETRIGGER_RELOAD_VAL          0
>> +#define RZN1_WDT_RETRIGGER_RELOAD_VAL_MASK     0xfff
>> +#define RZN1_WDT_RETRIGGER_PRESCALE            BIT(12)
>> +#define RZN1_WDT_RETRIGGER_ENABLE              BIT(13)
>> +#define RZN1_WDT_RETRIGGER_WDSI                        (0x2 << 14)
>> +
>> +#define RZN1_WDT_PRESCALER                     16384
>> +#define RZN1_WDT_MAX                           4095
>> +
>> +struct rzn1_watchdog {
>> +       struct watchdog_device          wdt;
>> +       void __iomem                    *base;
>> +       unsigned long                   clk_rate;
>> +};
>> +
>> +#define to_rzn1_watchdog(_ptr) \
>> +       container_of(_ptr, struct rzn1_watchdog, wdt)
>> +
>> +static inline uint32_t get_max_heart_beat(uint32_t clk_rate)
> unsigned long clk_rate
>
>> +{
>> +       return (RZN1_WDT_MAX * RZN1_WDT_PRESCALER) / (clk_rate / 1000);
> Is clk_rate always a multiple of 1000? If not, you want to reorder
> this to avoid losing precision.

The clock is 62.5 MHz, so dividing by 1000 doesn't cause a big precision 
loss.

I could use the 64bit division but it seemed less readable and the 
watchdog is

not used as a precise timer anyway.

>
>> +}
>> +static inline uint32_t compute_reload_value(uint32_t tick_ms, uint32_t clk)
> unsigned long clk_rate
>
>> +{
>> +       return (tick_ms * (clk / 1000)) / RZN1_WDT_PRESCALER;
> Likewise.
>
>> +}
>> +static int rzn1_wdt_probe(struct platform_device *pdev)
>> +{
>> +       struct device *dev = &pdev->dev;
>> +       struct rzn1_watchdog *wdt;
>> +       struct device_node *np = dev->of_node;
>> +       struct clk *clk;
>> +       int ret;
>> +       int irq;
>> +
>> +       wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
>> +       if (!wdt)
>> +               return -ENOMEM;
>> +
>> +       wdt->wdt = rzn1_wdt;
>> +       wdt->wdt.parent = dev;
>> +
>> +       wdt->base = devm_platform_ioremap_resource(pdev, 0);
>> +       if (IS_ERR(wdt->base))
>> +               return PTR_ERR(wdt->base);
>> +
>> +       irq = platform_get_irq(pdev, 0);
>> +       if (irq < 0) {
>> +               dev_err(dev, "failed to get the irq\n");
> No need to print a message, platform_get_irq() already does that.
>
>> +               return irq;
>> +       }
>> +
>> +       ret = devm_request_irq(dev, irq, rzn1_wdt_irq, 0,
>> +                              np->name, wdt);
>> +       if (ret) {
>> +               dev_err(dev, "failed to request irq %d\n", irq);
>> +               return ret;
>> +       }
>> +
>> +       clk = devm_clk_get(dev, NULL);
>> +       if (IS_ERR(clk)) {
>> +               dev_err(dev, "failed to get the clock\n");
>> +               return PTR_ERR(clk);
>> +       }
>> +
>> +       ret = clk_prepare_enable(clk);
>> +       if (ret) {
>> +               dev_err(dev, "failed to prepare/enable the clock\n");
>> +               return ret;
>> +       }
>> +
>> +       ret = devm_add_action_or_reset(dev, rzn1_wdt_clk_disable_unprepare,
>> +                                      clk);
>> +       if (ret) {
>> +               dev_err(dev, "failed to register clock unprepare callback\n");
>> +               clk_disable_unprepare(clk);
> Please drop this, as devm_add_action_or_reset() calls the
> action on failure.
>
>> +               return ret;
>> +       }
>> +
>> +       wdt->clk_rate = clk_get_rate(clk);
>> +       if (!wdt->clk_rate) {
>> +               dev_err(dev, "failed to get the clock rate\n");
>> +               return -EINVAL;
>> +       }
>> +
>> +       /*
>> +        * The period of the watchdog cannot be changed once set
>> +        * and is limited to a very short period.
>> +        * Configure it for a 1s period once and for all, and
>> +        * rely on the heart-beat provided by the watchdog core
>> +        * to make this usable by the user-space.
>> +        */
>> +       wdt->wdt.max_hw_heartbeat_ms = get_max_heart_beat(wdt->clk_rate);
>> +       if (wdt->wdt.max_hw_heartbeat_ms > 1000)
>> +               wdt->wdt.max_hw_heartbeat_ms = 1000;
>> +
>> +       wdt->wdt.timeout = DEFAULT_TIMEOUT;
>> +       ret = watchdog_init_timeout(&wdt->wdt, 0, dev);
>> +
>> +       return devm_watchdog_register_device(dev, &wdt->wdt);
>> +}
>> +
>> +
>> +static const struct of_device_id rzn1_wdt_match[] = {
>> +       { .compatible = "renesas,r9a06g032-wdt" },
> No need to match on the soc-specific compatible value, as the
> family-specific value should be present in the DTB, too.
>
>> +       { .compatible = "renesas,rzn1-wdt" },
>> +       {},
>> +};
>> +MODULE_DEVICE_TABLE(of, rzn1_wdt_match);
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds