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

From: Guenter Roeck
Date: Tue Aug 27 2019 - 09:06:38 EST

On 8/27/19 2:24 AM, Ivan Mikhaylov wrote:
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
+ * both versions of the SoC. For alternate boot mode (booted from CS1 due
+ * 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-



+ * 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,
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
status = readl(wdt->base + WDT_TIMEOUT_STATUS);
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

You said earlier that this can not be done automatically but _must_ be done
from user space after the system has booted. Otherwise you could just
automatically switch to cs0 when the driver probes.

As I said, all I am asking for is proper documentation.


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?