linux-kernel - Re: [PATCH] sbsa_gwdt: Calculate timeout with 64-bit math

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Message-ID: <1fae4d2c-4bc7-f169-7b84-501674a82ee4@roeck-us.net>
Date:   Sun, 22 Oct 2023 09:58:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Darren Hart <darren@...amperecomputing.com>
Cc:     linux-kernel@...r.kernel.org,
        Vanshidhar Konda <vanshikonda@...amperecomputing.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
Subject: Re: [PATCH] sbsa_gwdt: Calculate timeout with 64-bit math

On 10/14/23 02:12, Darren Hart wrote:
> On Tue, Sep 26, 2023 at 05:45:13AM -0700, Guenter Roeck wrote:
>> On Thu, Sep 21, 2023 at 02:02:36AM -0700, Darren Hart wrote:
>>> Commit abd3ac7902fb ("watchdog: sbsa: Support architecture version 1")
>>> introduced new timer math for watchdog revision 1 with the 48 bit offset
>>> register.
>>>
>>> The gwdt->clk and timeout are u32, but the argument being calculated is
>>> u64. Without a cast, the compiler performs u32 operations, truncating
>>> intermediate steps, resulting in incorrect values.
>>>
>>> A watchdog revision 1 implementation with a gwdt->clk of 1GHz and a
>>> timeout of 600s writes 3647256576 to the one shot watchdog instead of
>>> 300000000000, resulting in the watchdog firing in 3.6s instead of 600s.
>>>
>>> Force u64 math by casting the first argument (gwdt->clk) as a u64. Make
>>> the order of operations explicit with parenthesis.
>>>
>>> Fixes: abd3ac7902fb ("watchdog: sbsa: Support architecture version 1")
>>> Reported-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
>>> Signed-off-by: Darren Hart <darren@...amperecomputing.com>
>>> Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>
>>> Cc: Guenter Roeck <linux@...ck-us.net>
>>> Cc: linux-watchdog@...r.kernel.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: <stable@...r.kernel.org> # 5.14.x
>>
>> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> 
> Guenter or Wim, I haven't seen this land in the RCs or in next yet. Have
> you already picked it up? Anything more needed from me?
> 
> Thanks,
> 

Sorry, I am suffering from what I can only describe as a severe case of
maintainer/reviewer PTSD, and I have yet to find a way of dealing with that.

Guenter