linux-kernel - Re: watchdog: sp5100_tco support for AMD V/R/E series

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Date:   Mon, 7 Sep 2020 12:18:48 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jan Kiszka <jan.kiszka@...mens.com>, linux-watchdog@...r.kernel.org
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-kernel@...r.kernel.org,
        "Awan, Arsalan" <Arsalan_Awan@...tor.com>,
        "Hombourger, Cedric" <Cedric_Hombourger@...tor.com>,
        "Farnsworth, Wade" <wade_farnsworth@...tor.com>
Subject: Re: watchdog: sp5100_tco support for AMD V/R/E series

On 9/7/20 8:46 AM, Jan Kiszka wrote:
> On 07.09.20 17:31, Guenter Roeck wrote:
>> On 9/7/20 4:20 AM, Jan Kiszka wrote:
>>> Hi all,
>>>
>>> Arsalan reported that the upstream driver for sp5100_tco does not work
>>> for embedded Ryzen. Meanwhile, I was able to confirm that on an R1505G:
>>>
>>> [   11.607251] sp5100_tco: SP5100/SB800 TCO WatchDog Timer Driver
>>> [   11.607337] sp5100-tco sp5100-tco: Using 0xfed80b00 for watchdog MMIO address
>>> [   11.607344] sp5100-tco sp5100-tco: Watchdog hardware is disabled
>>>
>>> ..and fix it:
>>>
>>> diff --git a/drivers/watchdog/sp5100_tco.c b/drivers/watchdog/sp5100_tco.c
>>> index 85e9664318c9..5482154fde42 100644
>>> --- a/drivers/watchdog/sp5100_tco.c
>>> +++ b/drivers/watchdog/sp5100_tco.c
>>> @@ -193,7 +193,8 @@ static void tco_timer_enable(struct sp5100_tco *tco)
>>>  		/* Set the Watchdog timer resolution to 1 sec and enable */
>>>  		sp5100_tco_update_pm_reg8(EFCH_PM_DECODEEN3,
>>>  					  ~EFCH_PM_WATCHDOG_DISABLE,
>>> -					  EFCH_PM_DECODEEN_SECOND_RES);
>>> +					  EFCH_PM_DECODEEN_SECOND_RES |
>>> +					  EFCH_PM_DECODEEN_WDT_TMREN);
>>
>> Confusing. The register in question is a 32-bit register, but only a byte
>> is written into it. Bit 24-25 are supposed to be the resolution, bit 25-26
>> set to 0 enable the watchdog. Bit 7 is supposed to enable MMIO decoding.
>> This is from AMD Publication 52740. So something in the existing code
>> is (or seems to be) wrong, but either case I don't see how setting bit 7
>> (or 31 ?) would enable the watchdog hardware.
>>
>> Hmm, I wrote that code. Guess I'll need to to spend some time figuring out
>> what is going on.
> 
> The logic came from [1] which inspired [2] - that's where I pointed out
> the large overlap with the existing upstream driver. I would love to see
> all that consolidated.
> 
> BTW, the R1505G is family 0x17. Maybe something changed there, and that
> bit 7 was just reserved/ignored so far. ENOSPECS
> 

Thanks for the pointers.

I think you are talking about bit 31. Bit 7 is and was WatchdogTmrEn, but that
supposedly only enables watchdog timer memory access at 0xfeb00000. From what
I glance from the other drivers, the existing code is wrong. It should set
the disable and resolution bits in register offset 3 (bit 24..27), not 0.
In other words, EFCH_PM_DECODEEN3 should be defined as 0x03, not as 0x00.
Which actually makes sense from the name.

Playing with my hardware, turns out that setting bit 7 in EFCH_PM_DECODEEN
(register offset 0) does indeed enable the watchdog. I'll need to check
if it actually works. Either case, -ENOSPECS is really a problem here.

Guenter

> Jan
> 
> [1]
> https://git.yoctoproject.org/cgit/cgit.cgi/meta-amd/commit/meta-amd-bsp/recipes-kernel/amd-wdt/files/amd_wdt.c?id=cd760c9f04d276382a0f5156dabdb766594ace56
> [2]
> https://github.com/siemens/efibootguard/commit/3a702aa96d193f26571ea4e70db29ef01a0d4d5f
>