linux-kernel - Re: [PATCH] watchdog: bcm7038

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Date:   Mon, 22 Feb 2021 14:24:47 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Álvaro Fernández Rojas <noltari@...il.com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: bcm7038_wdt: add big endian support

On Mon, Feb 22, 2021 at 10:48:09PM +0100, Álvaro Fernández Rojas wrote:
> Hi Guenter,
> 
> > El 22 feb 2021, a las 22:24, Guenter Roeck <linux@...ck-us.net> escribió:
> > 
> > On 2/22/21 12:03 PM, Álvaro Fernández Rojas wrote:
> >> bcm7038_wdt can be used on bmips (bcm63xx) devices too.
> >> 
> > It might make sense to actually enable it for BCM63XX.
> 
> bcm63xx SoCs are supported in bcm63xx and bmips.
> bcm63xx doesn’t have device tree support, but bmips does and this watchdog is already enabled for bmips.
> 

Maybe add a note saying that this will only be supported for devicetree
based systems.

> > 
> >> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> >> ---
> >> drivers/watchdog/bcm7038_wdt.c | 30 ++++++++++++++++++++++++------
> >> 1 file changed, 24 insertions(+), 6 deletions(-)
> >> 
> >> diff --git a/drivers/watchdog/bcm7038_wdt.c b/drivers/watchdog/bcm7038_wdt.c
> >> index 979caa18d3c8..62494da1ac57 100644
> >> --- a/drivers/watchdog/bcm7038_wdt.c
> >> +++ b/drivers/watchdog/bcm7038_wdt.c
> >> @@ -34,6 +34,24 @@ struct bcm7038_watchdog {                                 
> >> 
> >> static bool nowayout = WATCHDOG_NOWAYOUT;
> >> 
> >> +static inline void bcm7038_wdt_write(unsigned long data, void __iomem *reg)
> >> +{
> >> +#ifdef CONFIG_CPU_BIG_ENDIAN
> >> +    __raw_writel(data, reg);
> >> +#else
> >> +    writel(data, reg);
> >> +#endif
> >> +}
> >> +
> >> +static inline unsigned long bcm7038_wdt_read(void __iomem *reg)
> >> +{
> >> +#ifdef CONFIG_CPU_BIG_ENDIAN
> >> +    return __raw_readl(reg);
> >> +#else
> >> +    return readl(reg);
> >> +#endif
> >> +}
> >> +
> > 
> > This needs further explanation. Why not just use __raw_writel() and
> > __raw_readl() unconditionally ? Also, is it known for sure that,
> > say, bmips_be_defconfig otherwise uses the wrong endianness
> > (vs. bmips_stb_defconfig which is a little endian configuration) ?
> 
> Because __raw_writel() doesn’t have memory barriers and writel() does.
> Those configs use the correct endiannes, so I don’t know what you mean...
> 
So are you saying that it already works with bmips_stb_defconfig 
(because it is little endian), that bmips_stb_defconfig needs memory
barriers, and that bmips_be_defconfig doesn't need memory barriers ?
Odd, but I'll take you by your word. And other code does something
similar, so I guess there must be a reason for it.

Anyway, after looking into that other code, please use something like

        if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
                __raw_writel(value, reg);
        else
                writel(value, reg);

Thanks,
Guenter

> > 
> > Thanks,
> > Guenter
> > 
> >> static void bcm7038_wdt_set_timeout_reg(struct watchdog_device *wdog)
> >> {
> >>    struct bcm7038_watchdog *wdt = watchdog_get_drvdata(wdog);
> >> @@ -41,15 +59,15 @@ static void bcm7038_wdt_set_timeout_reg(struct watchdog_device *wdog)
> >> 
> >>    timeout = wdt->rate * wdog->timeout;
> >> 
> >> -    writel(timeout, wdt->base + WDT_TIMEOUT_REG);
> >> +    bcm7038_wdt_write(timeout, wdt->base + WDT_TIMEOUT_REG);
> >> }
> >> 
> >> static int bcm7038_wdt_ping(struct watchdog_device *wdog)
> >> {
> >>    struct bcm7038_watchdog *wdt = watchdog_get_drvdata(wdog);
> >> 
> >> -    writel(WDT_START_1, wdt->base + WDT_CMD_REG);
> >> -    writel(WDT_START_2, wdt->base + WDT_CMD_REG);
> >> +    bcm7038_wdt_write(WDT_START_1, wdt->base + WDT_CMD_REG);
> >> +    bcm7038_wdt_write(WDT_START_2, wdt->base + WDT_CMD_REG);
> >> 
> >>    return 0;
> >> }
> >> @@ -66,8 +84,8 @@ static int bcm7038_wdt_stop(struct watchdog_device *wdog)
> >> {
> >>    struct bcm7038_watchdog *wdt = watchdog_get_drvdata(wdog);
> >> 
> >> -    writel(WDT_STOP_1, wdt->base + WDT_CMD_REG);
> >> -    writel(WDT_STOP_2, wdt->base + WDT_CMD_REG);
> >> +    bcm7038_wdt_write(WDT_STOP_1, wdt->base + WDT_CMD_REG);
> >> +    bcm7038_wdt_write(WDT_STOP_2, wdt->base + WDT_CMD_REG);
> >> 
> >>    return 0;
> >> }
> >> @@ -88,7 +106,7 @@ static unsigned int bcm7038_wdt_get_timeleft(struct watchdog_device *wdog)
> >>    struct bcm7038_watchdog *wdt = watchdog_get_drvdata(wdog);
> >>    u32 time_left;
> >> 
> >> -    time_left = readl(wdt->base + WDT_CMD_REG);
> >> +    time_left = bcm7038_wdt_read(wdt->base + WDT_CMD_REG);
> >> 
> >>    return time_left / wdt->rate;
> >> }
> >> 
> >