> -----Original Message----- > From: Marco Felsch <m.felsch@xxxxxxxxxxxxxx> > Sent: Thursday, August 25, 2022 3:50 PM > To: Alice Guo (OSS) <alice.guo@xxxxxxxxxxx> > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>; wim@xxxxxxxxxxxxxxxxxx; > shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx; > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > dl-linux-imx <linux-imx@xxxxxxx>; kernel@xxxxxxxxxxxxxx; > linux-watchdog@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for > unlock sequence > > On 22-08-24, Alice Guo (OSS) wrote: > > > > > -----Original Message----- > > > From: Marco Felsch <m.felsch@xxxxxxxxxxxxxx> > > > Sent: Wednesday, August 24, 2022 5:06 PM > > > To: Alice Guo (OSS) <alice.guo@xxxxxxxxxxx> > > > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>; wim@xxxxxxxxxxxxxxxxxx; > > > shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx; > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > > dl-linux-imx <linux-imx@xxxxxxx>; kernel@xxxxxxxxxxxxxx; > > > linux-watchdog@xxxxxxxxxxxxxxx > > > 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@xxxxxxxxxxxxxx> > > > > > Sent: Wednesday, August 24, 2022 4:04 PM > > > > > To: Alice Guo (OSS) <alice.guo@xxxxxxxxxxx> > > > > > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>; wim@xxxxxxxxxxxxxxxxxx; > > > > > shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; > festevam@xxxxxxxxx; > > > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > > > > > linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; > > > > > kernel@xxxxxxxxxxxxxx; linux-watchdog@xxxxxxxxxxxxxxx > > > > > 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 Hi Marco, The ROM code of i.MX7ULP configures the WDOG to support 16-bit unlock command. I plan to add a comment to explain it in code, and keep "mb(); writel_relaxed; writel_relaxed; mb()" unchanged. Best Regards, Alice Guo
