[U-Boot] [U-Boot,V2] imx: mx7: psci: add system reset support

[Peng Fan]

> -----Original Message-----
> From: Trent Piepho [mailto:tpiepho at impinj.com]
> Sent: 2018年5月9日 4:11
> To: Peng Fan <peng.fan at nxp.com>; christian.gmeiner at gmail.com; Anson
> Huang <anson.huang at nxp.com>; u-boot at lists.denx.de;
> albert.u.boot at aribaud.net; sbabic at denx.de
> Cc: Fabio Estevam <fabio.estevam at nxp.com>
> Subject: Re: [U-Boot,V2] imx: mx7: psci: add system reset support
> 
> On Tue, 2018-05-08 at 05:29 +0000, Peng Fan wrote:
> > > -----Original Message-----
> > > From: Trent Piepho [mailto:tpiepho at impinj.com]
> > > Sent: 2018年5月8日 6:07
> > > To: christian.gmeiner at gmail.com; Peng Fan <peng.fan at nxp.com>; Anson
> > > Huang <anson.huang at nxp.com>; u-boot at lists.denx.de;
> > > albert.u.boot at aribaud.net; sbabic at denx.de
> > > Cc: Fabio Estevam <fabio.estevam at nxp.com>
> > > Subject: Re: [U-Boot,V2] imx: mx7: psci: add system reset support
> > >
> > > On Thu, 2018-01-04 at 17:03 +0800, Anson Huang wrote:
> > > > Add i.MX7 PSCI system reset support, linux kernel now can use "reboot"
> > > > command to reset system.
> > >
> > >
> > > > +__secure void imx_system_reset(void) {
> > > > +	writew(1 << 2, WDOG1_BASE_ADDR); }
> > >
> > > This does not work properly on our board.
> >
> > You could try write 0x14 to WDOG1_BASE_ADDR to see whether it works.
> > Here using (1 << 2) triggers both SRS and WDOG_B which seems wrong.
> 
> It works when the Linux driver does that and appears to work identically when
> uboot does it that way.
> 
> Triggering both SRS and WDOG_B does not work as it causes a very short
> wdog_b assertion.

Yes.

> 
> There is a little difficulty here in just changing the code to use
> WCR_WDE|WCR_SRS, as that would be wrong if the board does not use an
> external signal.  The Linux driver uses the device tree to determine what to do,
> but this will not work for PSCI.

U-Boot need parse the device tree and configure the WDOG accordingly.

-Peng

> 
> > > Due to an erratum in iMX7d it is necessary to wire the external
> > > WDOG_B signal to the pmic to cycle power in order to reset the
> > > board.  The Linux IMX watchdog driver works when it does a reboot
> > > via the watchdog, but this code does not.
> > >
> > > When the Linux drivers is configured for an external wdog signal,
> > > using a DT property, it sets WCR_SRS to prevent the internal system
> > > reset in response to watchdog triggering.  When that is not done, as
> > > in this patch, the internal reset appears to reset the wdog module
> > > or iomux or something, which causes the imx7d to stop asserting the
> > > external wdog signal.
> > >
> > > In my tests, this takes only about 2.4 µs.  Such a short wdog_b
> > > pulse does not appear to be sufficient to trigger the pmic to cycle power.
> > >
> > > When SRS is set, then the WDOG_B signal will remain asserted until
> > > the POR_B input signal to the imx7d is asserted.  I.e., until pmic
> > > responds to the watchdog signal.