From: Marco Felsch <m.felsch@pengutronix.de>
To: "Alice Guo (OSS)" <alice.guo@oss.nxp.com>
Cc: Guenter Roeck <linux@roeck-us.net>,
"wim@linux-watchdog.org" <wim@linux-watchdog.org>,
"shawnguo@kernel.org" <shawnguo@kernel.org>,
"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
"festevam@gmail.com" <festevam@gmail.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
dl-linux-imx <linux-imx@nxp.com>,
"kernel@pengutronix.de" <kernel@pengutronix.de>,
"linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>
Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence
Date: Thu, 25 Aug 2022 09:50:16 +0200 [thread overview]
Message-ID: <20220825075016.rhwvlfl6xv2ibro3@pengutronix.de> (raw)
In-Reply-To: <AM6PR04MB605317170101019C75BA9290E2739@AM6PR04MB6053.eurprd04.prod.outlook.com>
On 22-08-24, Alice Guo (OSS) wrote:
>
> > -----Original Message-----
> > From: Marco Felsch <m.felsch@pengutronix.de>
> > Sent: Wednesday, August 24, 2022 5:06 PM
> > To: Alice Guo (OSS) <alice.guo@oss.nxp.com>
> > Cc: Guenter Roeck <linux@roeck-us.net>; wim@linux-watchdog.org;
> > shawnguo@kernel.org; s.hauer@pengutronix.de; festevam@gmail.com;
> > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> > dl-linux-imx <linux-imx@nxp.com>; kernel@pengutronix.de;
> > linux-watchdog@vger.kernel.org
> > Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for
> > unlock sequence
> >
> > Hi Alice,
> >
> > On 22-08-24, Alice Guo (OSS) wrote:
> > > > -----Original Message-----
> > > > From: Marco Felsch <m.felsch@pengutronix.de>
> > > > Sent: Wednesday, August 24, 2022 4:04 PM
> > > > To: Alice Guo (OSS) <alice.guo@oss.nxp.com>
> > > > Cc: Guenter Roeck <linux@roeck-us.net>; wim@linux-watchdog.org;
> > > > shawnguo@kernel.org; s.hauer@pengutronix.de; festevam@gmail.com;
> > > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> > > > dl-linux-imx <linux-imx@nxp.com>; kernel@pengutronix.de;
> > > > linux-watchdog@vger.kernel.org
> > > > Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory
> > > > barrier for unlock sequence
> > > >
> > > > Hi Alice,
> > > >
> > > > On 22-08-24, Alice Guo (OSS) wrote:
> > > >
> > > > ...
> > > >
> > > > > > > > Hi Guenter and Marco,
> > > > > > > >
> > > > > > > > 1. did you see any issues?
> > > > > > > > This WDOG Timer first appeared in i.MX7ULP, no one report
> > > > > > > > issues probably because few people use i.MX7ULP. This issue
> > > > > > > > was found when we did a stress test on it. When we
> > > > > > > > reconfigure the WDOG Timer, there is a certain probability
> > > > > > > > that it reset. The reason for the error is that when
> > > > > > > > WDOG_CS[CMD32EN] is 0, the unlock sequence is two 16-bit
> > > > > > > > writes (0xC520, 0xD928) to the CNT register within 16 bus
> > > > > > > > clocks, and improper unlock sequence causes the
> > > > WDOG to reset.
> > > > > > > > Adding mb() is to guarantee that two 16-bit writes are
> > > > > > > > finished within 16
> > > > > > bus clocks.
> > > > > > >
> > > > > > > After this explanation the whole imx7ulp_wdt_init() seems a
> > > > > > > bit buggy because writel_relaxed() as well as writel() are
> > > > > > > 32bit access
> > > > functions.
> > > > > > > So the very first thing to do is to enable the 32-bit mode.
> > > > > > >
> > > > > > Agreed. This is much better than having extra code to deal with
> > > > > > both 16-bit and 32-bit access.
> > > > > >
> > > > > > > Also this is a explanation worth to be added to the commit
> > > > > > > message
> > > > > > > ;)
> > > > > > >
> > > > > >
> > > > > > Definitely. Also, the use of mb(), if it should indeed be
> > > > > > needed, would have to be explained in a code comment.
> > > > > >
> > > > > > Thanks,
> > > > > > Guenter
> > > > >
> > > > > Hi Marco and Guenter,
> > > > >
> > > > > Thank you for your comments. I plan to enable support for 32-bit
> > > > > unlock command write words in bootloader. In this way, there is no
> > > > > need to distinguish whether the unlock command is a 32-bit command
> > > > > or a 16-bit command in driver.
> > > >
> > > > Please don't move this into the bootloader, enabling it within the
> > > > init seq. is just fine. If you move it into the bootloader then you
> > > > can't ensure that the bit is set since there are plenty of bootloaders out
> > there.
> > > >
> > > > As I said, just drop the "16bit" unlock sequence from the init
> > > > function because the unlock is handled just fine in all the watchdog_ops.
> > > >
> > > > Regards,
> > > > Marco
> > >
> > > Hi Marco,
> > >
> > > Sorry, I did not tell you that all watchdog control bits, timeout
> > > value, and window value cannot be set until the watchdog is unlocked.
> >
> > You don't have to according the RM:
> > 8<----------------------------------------------------------------------
> > 59.5.2 Disable Watchdog after Reset
> >
> > All of watchdog registers are unlocked by reset. Therefore, unlock sequence is
> > unnecessary, but it needs to write all of watchdog registers to make the new
> > configuration take effect. The code snippet below shows an example of
> > disabling watchdog after reset.
> > 8<----------------------------------------------------------------------
> >
> > also the RM tells us:
> > 8<----------------------------------------------------------------------
> > 59.4.3.1 Configuring the Watchdog Once
> >
> > The new configuration takes effect only after all registers except CNT are
> > written after reset. Otherwise, the WDOG uses the reset values by default. If
> > window mode is not used (CS[WIN] is 0), writing to WIN is not required to
> > make the new configuration take effect.
> > 8<----------------------------------------------------------------------
> >
> > > Support for 32-bit unlock command write words in enabled in
> > > imx7ulp_wdt_init now.
> >
> > So.. after reading the IMX7ULP RM, which was not my intention, I found out
> > that most of the WDOG_CS regiter bits are write-once bits. This means if you
> > didn't set it within the bootloader you still in case "59.4.3.1".
> >
> > So the imx7ulp_wdt_init() function just needs to check if the
> > WDOG_CS_UPDATE bit was set. If it is not the case, then you need to write the
> > WDOG_CS register as currently done. If the bit is set, than you need know that
> > the bootloader did the job for you and you can exit
> > imx7ulp_wdt_init() early. In both cases the unlock is not required.
> >
> > Can you please check/test if this is working for you?
> >
> > Regards,
> > Marco
> >
>
> Hi Marco,
>
> Rom code has already configured the WDOG once, so we cannot use "
> Configuring the Watchdog Once".
What? How does the ROM code configure the WDOG? Also this would be worth a
comment within the code. Also still assume that this "16bit unlock" seq.
is useless since you writing 32bit anyway.
Regards,
Marco
next prev parent reply other threads:[~2022-08-25 7:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-16 4:36 [PATCH 0/7] watchdog: imx7ulp_wdt: update i.MX7ULP WDOG timer driver Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 1/7] watchdog: imx7ulp: Move suspend/resume to noirq phase Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence Alice Guo (OSS)
2022-08-16 6:23 ` Marco Felsch
2022-08-22 7:49 ` Alice Guo (OSS)
2022-08-22 8:00 ` Marco Felsch
2022-08-22 14:03 ` Guenter Roeck
2022-08-23 5:38 ` Alice Guo (OSS)
2022-08-23 9:10 ` Marco Felsch
2022-08-23 12:02 ` Guenter Roeck
2022-08-24 6:24 ` Alice Guo (OSS)
2022-08-24 8:03 ` Marco Felsch
2022-08-24 8:40 ` Alice Guo (OSS)
2022-08-24 9:06 ` Marco Felsch
2022-08-24 10:05 ` Alice Guo (OSS)
2022-08-25 7:50 ` Marco Felsch [this message]
2022-08-25 8:08 ` Alice Guo (OSS)
2022-08-25 9:01 ` Marco Felsch
2022-08-25 10:11 ` Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 3/7] watchdog: imx7ulp_wdt: Check CMD32EN in wdog init Alice Guo (OSS)
2022-08-22 14:05 ` Guenter Roeck
2022-08-23 5:46 ` Alice Guo (OSS)
2022-08-23 12:05 ` Guenter Roeck
2022-08-16 4:36 ` [PATCH 4/7] watchdog: imx7ulp_wdt: Fix RCS timeout issue Alice Guo (OSS)
2022-08-22 14:09 ` Guenter Roeck
2022-08-23 5:59 ` Alice Guo (OSS)
2022-08-23 12:06 ` Guenter Roeck
2022-08-24 6:44 ` Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 5/7] watchdog: imx7ulp_wdt: Handle wdog reconfigure failure Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 6/7] watchdog: imx7ulp_wdt: init wdog when it was active Alice Guo (OSS)
2022-08-16 4:36 ` [PATCH 7/7] watchdog: imx93: add watchdog timer on imx93 Alice Guo (OSS)
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