linux-kernel - Re: [PATCH v2 3/4] watchdog/aspeed: add support for dual boot

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Date:   Tue, 27 Aug 2019 12:24:45 +0300
From:   Ivan Mikhaylov <i.mikhaylov@...ro.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
CC:     Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...id.au>,
        <linux-watchdog@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-aspeed@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
        "Alexander Amelkin" <a.amelkin@...ro.com>,
        <openbmc@...ts.ozlabs.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] watchdog/aspeed: add support for dual boot

On Mon, 2019-08-26 at 17:14 -0700, Guenter Roeck wrote:
> > +/*
> > + * At alternate side the 'access_cs0' sysfs node provides:
> > + *   ast2400: a way to get access to the primary SPI flash chip at CS0
> > + *            after booting from the alternate chip at CS1.
> > + *   ast2500: a way to restore the normal address mapping from
> > + *            (CS0->CS1, CS1->CS0) to (CS0->CS0, CS1->CS1).
> > + *
> > + * Clearing the boot code selection and timeout counter also resets to the
> > + * initial state the chip select line mapping. When the SoC is in normal
> > + * mapping state (i.e. booted from CS0), clearing those bits does nothing
> > for
> > + * both versions of the SoC. For alternate boot mode (booted from CS1 due
> > to
> > + * wdt2 expiration) the behavior differs as described above.
> > + *
> The above needs to be in the sysfs attribute documentation as well.

My apologies but I didn't find any suitable, only watchdog parameters with
dtbindings file, where should I put it? Documentation/watchdog/aspeed-wdt-
sysfs.rst?

> > + * This option can be used with wdt2 (watchdog1) only.
> 
> This implies a specific watchdog numbering which is not guaranteed.
> Someone might implement a system with some external watchdog.
> 
> > + */
> > +static DEVICE_ATTR_RW(access_cs0);
> > +
> > +static struct attribute *bswitch_attrs[] = {
> > +	&dev_attr_access_cs0.attr,
> > +	NULL
> > +};
> > +ATTRIBUTE_GROUPS(bswitch);
> > +
> >   static const struct watchdog_ops aspeed_wdt_ops = {
> >   	.start		= aspeed_wdt_start,
> >   	.stop		= aspeed_wdt_stop,
> > @@ -306,9 +359,16 @@ static int aspeed_wdt_probe(struct platform_device
> > *pdev)
> >   	}
> >   
> >   	status = readl(wdt->base + WDT_TIMEOUT_STATUS);
> > -	if (status & WDT_TIMEOUT_STATUS_BOOT_SECONDARY)
> > +	if (status & WDT_TIMEOUT_STATUS_BOOT_SECONDARY) {
> >   		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> >   
> > +		if (of_device_is_compatible(np, "aspeed,ast2400-wdt") ||
> > +			of_device_is_compatible(np, "aspeed,ast2500-wdt"))
> > +			wdt->wdd.groups = bswitch_groups;

> Kind of odd that the attribute only exists if the system booted from the
> second flash, but if that is what you want I won't object. Just make sure
> that this is explained properly.
Perhaps dts configuration option would be better solution for it then? "force-
cs0-switch" as example? Also, if it would be an option, dtbindings/wdt file for
documentation will be the right place for it. Usage of this at side 0 will not
get any good/bad results, it just makes user confused, so I decided to put it
only at side 1. It works only for ast2400/2500 board unfortunately, for 2600
there is big difference in switching mechanism. Any other thoughts how to make
it better?

Thanks.