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Subject: Re: watchdog: sp5100_tco support for AMD V/R/E series
To:     Jan Kiszka <jan.kiszka@siemens.com>, linux-watchdog@vger.kernel.org
Cc:     Wim Van Sebroeck <wim@linux-watchdog.org>,
        linux-kernel@vger.kernel.org,
        "Awan, Arsalan" <Arsalan_Awan@mentor.com>,
        "Hombourger, Cedric" <Cedric_Hombourger@mentor.com>,
        "Farnsworth, Wade" <wade_farnsworth@mentor.com>
References: <15c8913e-9026-2649-9911-71d6f1c79519@siemens.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <f7e3233b-97e4-1f25-e18e-edb39ca86ce9@roeck-us.net>
Date:   Mon, 7 Sep 2020 08:31:51 -0700
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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.

Guenter

>  		break;
>  	}
>  }
> 
> Does anyone have an idea if such unconditional setting could be 
> problematic on older/different efch? We probe for that bit in
> sp5100_tco_setupdevice but we never set it so far.
> 
> I'm missing specs...
> 
> Thanks,
> Jan
>