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

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Date:   Wed, 9 Sep 2020 09:04:39 -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 1:45 PM, Guenter Roeck wrote:
> On 9/7/20 12:18 PM, Guenter Roeck wrote:
>> 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.
>>
> 
> ... and it does work. After playing with it, it seems that on Family 17h
> CPUs EFCH_PM_DECODEEN_WDT_TMREN not only enables watchdog timer memory
> access at 0xfeb0000, but also enables the watchdog itself.
> 
> Also, turns out the documentation is now public, at least for some of the
> Family 17h CPUs (though oddly enough not for all of them). See processor
> reference manuals at https://www.amd.com/en/support/tech-docs. The documents
> for model 18h and model 20h include a note stating that bit 7 of
> EFCH_PM_DECODEEN enables both memory access and the watchdog hardware.
> 
> So we'll need two patches - one to fix the value of EFCH_PM_DECODEEN3,
> and one to enable the watchdog bit setting bit 7 of EFCH_PM_DECODEEN
> for Family 17h CPUs.
> 
Jan - any chance you can submit those patches ? Or do you want me to do it ?

Thanks,
Guenter

> Thanks,
> Guenter
> 
>> 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
>>>
>>
>