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Sender: Guenter Roeck <groeck7@gmail.com>
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Date:   Sun, 22 Oct 2023 09:58:26 -0700
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Subject: Re: [PATCH] sbsa_gwdt: Calculate timeout with 64-bit math
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To:     Darren Hart <darren@os.amperecomputing.com>
Cc:     linux-kernel@vger.kernel.org,
        Vanshidhar Konda <vanshikonda@os.amperecomputing.com>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org
References: <7d1713c5ffab19b0f3de796d82df19e8b1f340de.1695286124.git.darren@os.amperecomputing.com>
 <bcc41311-075c-44fe-b0f7-30564d7ac58c@roeck-us.net> <ZSpbfXzFeaoUJRZ3@Fedora>
From:   Guenter Roeck <linux@roeck-us.net>
In-Reply-To: <ZSpbfXzFeaoUJRZ3@Fedora>
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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@os.amperecomputing.com>
>>> Signed-off-by: Darren Hart <darren@os.amperecomputing.com>
>>> Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
>>> Cc: Guenter Roeck <linux@roeck-us.net>
>>> Cc: linux-watchdog@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Cc: linux-arm-kernel@lists.infradead.org
>>> Cc: <stable@vger.kernel.org> # 5.14.x
>>
>> Reviewed-by: Guenter Roeck <linux@roeck-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