Re: PSCI version 1.1 and SYSTEM_RESET2

[Sodagudi Prasad]

On 2019-05-02 02:05, Sudeep Holla wrote:
> On Wed, May 01, 2019 at 11:43:00AM -0700, Sodagudi Prasad wrote:
> > On 2019-05-01 02:49, Sudeep Holla wrote:
> > > On Tue, Apr 30, 2019 at 05:07:31PM -0700, Sodagudi Prasad wrote:
> > > > On 2019-04-30 14:44, Sodagudi Prasad wrote:
>
> [...]
>
> > > >
> > > > It would nice if there is a config option to reboot the device
> > > > either in
> > > > warm or cold in the case of kernel panic.
> > >
> > > I presume you prefer to do warm boot in case of panic to get a dump of
> > > the memory to inspect ? If so, is kexec/kdump not the mechanism to
> > > achieve that ?
> >
> > Hi Sudeep,
> >
> > Thanks for your response and sharing details about your patch.
> >
> > > If so, is kexec/kdump not the mechanism to achieve that?
> > >
> > Qualcomm is having vendor specific solution to capture ram contents 
> > and for
> > offline analysis.
>
> Ah OK.
>
> > >
> > > I am just trying to understand the use case. Xilinx asked for the same
> > > but never got to understand their use case.
> >
> > Here is the background -
> > Usually, power off drivers are overriding arm_pm_restart and 
> > pm_power_off
> > callbacks and registering with reboot notifier with  some priority for 
> > the
> > reboot operations.  Here is the Qualcomm poweroff driver for 
> > reference.
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/power/reset/msm-poweroff.c
> >
> > Before vendor chip set specific power off driver is probed, 
> > arm_pm_restart
> > functions pointer holds the psci_sys_reset function. Once vendor power 
> > off
> > driver is probed,  vendor drivers can override the arm_pm_restart 
> > function
> > pointer.
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/psci.c#n562
> >
> > Once vendor driver is probed, drivers can take care of devices warm or 
> > hard
> > reset configuration part properly.  But there is a window from
> > start_kernel() to vendor specific driver probed, devices are getting 
> > cold
> > resets even if kernel crashed.  This is due to arm_pm_restart points 
> > to
> > psci_sys_reset function by default.  Is this problem clear now?
>
> Too specific use case IMO and I am not sure if we need a generic 
> solution
> to deal with this. Anyways, I don't see any check in arch/psci specific
> code for what you want, just ensure reboot_mode is set appropriately.
> Post a patch and see what people have to say.

Hi Sudeep,

Yes. With your system_reset2 command support addition, just configuring 
the reboot_mode is good enough.

-Thanks, Prasad

> > Qualcomm downstream kernel has a lot of use cases with respect device 
> > reset
> > sequence and the downstream driver is much different from upstream 
> > drivers.
> > I think, the above-mentioned problem is common for all the chipset 
> > vendors
> > and it is not specific Qualcomm use cases.  I have one downstream 
> > solution
> > to this problem but thought to bring up this problem to the upstream
> > community for a common solution, so that all the vendors can use it.
>
> May be or may be not, post the patch and let's see.
>
> > I have modified below flow to avoid cold restart in the case of early 
> > kernel
> > panic.
> > panic() --> emergency_restart() --> machine_emergency_restart() -->
> > machine_restart(NULL);
> >
> > -Thanks, Prasad
> >
> > >
> > > --
> > > Regards,
> > > Sudeep
> >
> > --
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
> > Forum,
> > Linux Foundation Collaborative Project

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
Linux Foundation Collaborative Project