linux-kernel - Re: [PATCH RFC] watchdog: sbsa: Update the W

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Message-ID: <62e7db76-6baf-45a3-8a45-eae71a1b53c9@nvidia.com>
Date: Wed, 5 Nov 2025 08:37:18 -0800
From: Aaron Plattner <aplattner@...dia.com>
To: Andre Przywara <andre.przywara@....com>,
 Naina Mehta <naina.mehta@....qualcomm.com>, wim@...ux-watchdog.org,
 linux@...ck-us.net
Cc: linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] watchdog: sbsa: Update the W_IIDR Implementer bit
 mask to 0xFFF

On 11/4/25 4:00 AM, Andre Przywara wrote:
> Hi,
>
> On 04/11/2025 06:39, Naina Mehta wrote:
>> We noticed that the implementer mask defined in the driver [1] captures
>> bits 0-10, whereas section C.4.2 of BSA specification [2] indicates that
>> bits 0-11 of the W_IIDR register represent the implementer JEP106 code.
>>
>> We were hoping to understand if there is a specific reason for using
>> 11-bits in the driver implementation.
>>
>> Looking forward to your insights.
>
> Well, looks like a simple off-by-one bug, doesn't it? And nobody 
> noticed because it only affects vendors in the later JEP banks, and 
> the only user so far is comparing with 0x426, so it's not affected.

Yes, I think you're right. Sorry about that.

As far as I know, there isn't a 0xc26 assigned so I doubt anyone will 
run into this. And if they do, the workaround it applies has very low 
impact.

>
>>
>> [1] #define SBSA_GWDT_IMPL_MASK    0x7FF
>>
>> [2] Implementer, bits [11:0]
>>      Contains the JEP106 code of the company that implemented the 
>> Generic
>>      Watchdog:
>>      Bits[11:8] The JEP106 continuation code of the implementer.
>>      Bit[7] Always 0
>>      Bits [6:0] The JEP106 identity code of the implementer.
>>
>> Signed-off-by: Naina Mehta <naina.mehta@....qualcomm.com>
>> ---
>>   drivers/watchdog/sbsa_gwdt.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c
>> index 6ce1bfb39064..80cb166582df 100644
>> --- a/drivers/watchdog/sbsa_gwdt.c
>> +++ b/drivers/watchdog/sbsa_gwdt.c
>> @@ -75,7 +75,7 @@
>>   #define SBSA_GWDT_VERSION_MASK  0xF
>>   #define SBSA_GWDT_VERSION_SHIFT 16
>>   -#define SBSA_GWDT_IMPL_MASK    0x7FF
>> +#define SBSA_GWDT_IMPL_MASK    0xFFF
>
> Can we please use GENMASK here? This probably would have avoided the 
> problem in the first place.

I'll leave that up to the maintainers, but assuming they're okay with 
this quick fix,

Acked-by: Aaron Plattner <aplattner@...dia.com>

-- Aaron

>
> Cheers,
> Andre
>
>
>>   #define SBSA_GWDT_IMPL_SHIFT    0
>>   #define SBSA_GWDT_IMPL_MEDIATEK    0x426
>
>