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

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Message-ID: <0df27d36-b45f-2059-6ead-a09ceb4b7605@roeck-us.net>
Date:   Mon, 26 Aug 2019 17:14:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ivan Mikhaylov <i.mikhaylov@...ro.com>,
        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 8/26/19 3:46 AM, Ivan Mikhaylov wrote:
> Set WDT_CLEAR_TIMEOUT_AND_BOOT_CODE_SELECTION into WDT_CLEAR_TIMEOUT_STATUS
> to clear out boot code source and re-enable access to the primary SPI flash
> chip while booted via wdt2 from the alternate chip.
> 
> AST2400 datasheet says:
> "In the 2nd flash booting mode, all the address mapping to CS0# would be
> re-directed to CS1#. And CS0# is not accessable under this mode. To access
> CS0#, firmware should clear the 2nd boot mode register in the WDT2 status
> register WDT30.bit[1]."
> 
> Signed-off-by: Ivan Mikhaylov <i.mikhaylov@...ro.com>
> ---
>   drivers/watchdog/aspeed_wdt.c | 62 ++++++++++++++++++++++++++++++++++-
>   1 file changed, 61 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/aspeed_wdt.c b/drivers/watchdog/aspeed_wdt.c
> index cc71861e033a..bbc42847c0e3 100644
> --- a/drivers/watchdog/aspeed_wdt.c
> +++ b/drivers/watchdog/aspeed_wdt.c
> @@ -53,6 +53,8 @@ MODULE_DEVICE_TABLE(of, aspeed_wdt_of_table);
>   #define   WDT_CTRL_ENABLE		BIT(0)
>   #define WDT_TIMEOUT_STATUS	0x10
>   #define   WDT_TIMEOUT_STATUS_BOOT_SECONDARY	BIT(1)
> +#define WDT_CLEAR_TIMEOUT_STATUS	0x14
> +#define   WDT_CLEAR_TIMEOUT_AND_BOOT_CODE_SELECTION	BIT(0)
>   
>   /*
>    * WDT_RESET_WIDTH controls the characteristics of the external pulse (if
> @@ -165,6 +167,57 @@ static int aspeed_wdt_restart(struct watchdog_device *wdd,
>   	return 0;
>   }
>   
> +/* access_cs0 shows if cs0 is accessible, hence the reverted bit */
> +static ssize_t access_cs0_show(struct device *dev,
> +		struct device_attribute *attr, char *buf)

This and other multi-line declarations do not appear to be aligned
with '('.

> +{
> +	struct aspeed_wdt *wdt = dev_get_drvdata(dev);
> +	uint32_t status = readl(wdt->base + WDT_TIMEOUT_STATUS);
> +
> +	return sprintf(buf, "%u\n",
> +			!(status & WDT_TIMEOUT_STATUS_BOOT_SECONDARY));
> +}
> +
> +static ssize_t access_cs0_store(struct device *dev,
> +			      struct device_attribute *attr,
> +			      const char *buf, size_t size)
> +{
> +	struct aspeed_wdt *wdt = dev_get_drvdata(dev);
> +	unsigned long val;
> +
> +	if (kstrtoul(buf, 10, &val))
> +		return -EINVAL;
> +
> +	if (val)
> +		writel(WDT_CLEAR_TIMEOUT_AND_BOOT_CODE_SELECTION,
> +			wdt->base + WDT_CLEAR_TIMEOUT_STATUS);
> +
> +	return size;
> +}
> +
> +/*
> + * 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.

> + * 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.

> +	}
> +
> +	dev_set_drvdata(dev, wdt);
> +
>   	return devm_watchdog_register_device(dev, &wdt->wdd);
>   }
>   
>