linux-kernel - Re: [PATCH] watchdog: aspeed: Add sysfs attributes for reset mask bits

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Message-ID: <85ddf493-934f-75c4-7a3a-728289c1ee09@roeck-us.net>
Date:   Thu, 21 Sep 2023 21:24:40 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andrew Jeffery <andrew@...econstruct.com.au>,
        Zev Weiss <zev@...ilderbeest.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...id.au>
Cc:     linux-watchdog@...r.kernel.org, linux-aspeed@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        openbmc@...ts.ozlabs.org,
        Thomas Weißschuh <linux@...ssschuh.net>,
        Eddie James <eajames@...ux.ibm.com>,
        Ivan Mikhaylov <i.mikhaylov@...ro.com>
Subject: Re: [PATCH] watchdog: aspeed: Add sysfs attributes for reset mask
 bits

On 9/21/23 21:16, Andrew Jeffery wrote:
> On Thu, 2023-09-21 at 18:35 -0700, Zev Weiss wrote:
>> The AST2500 and AST2600 watchdog timers provide the ability to control
>> which devices are reset by the watchdog timer via a reset mask
>> resgister.  Previously the driver ignored that register, leaving
>> whatever configuration it found at boot and offering no way of
>> altering its settings.  Add a 'reset_ctrl' sysfs subdirectory with a
>> file per bit so that userspace can determine which devices the reset
>> is applied to.
>>
>> Note that not all bits in the hardware register are exposed -- in
>> particular, the ARM CPU and SOC/misc reset bits are left hidden since
>> clearing them can render the system unable to reboot.
>>
>> Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
>> ---
>>
>> I'm porting OpenBMC to a platform that requires that the LPC controller remain
>> un-reset by a BMC reboot.  With this patch userspace can control the reset
>> mask of the Aspeed watchdog timer, with a few bits remaining unexposed so as
>> to prevent some almost-certainly undesirable situations.  If there are other
>> bits that people feel shouldn't be exposed (or conversely if someone feels
>> strongly that the "dangerous" bits _should_ be exposed) I can adjust
>> accordingly.
> 
> 
> Is there a reason this has to be managed by userspace? It sounds a lot
> like a property of platform design, in which case exposing this feature
> in the devicetree might be a better approach.
> 

Same sentiment here.

Guenter