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SubjectRe: PSCI version 1.1 and SYSTEM_RESET2
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:
>> +Sudeep
>>
>> > Hi Mark/Will,
>> >
>> > I would like to understand whether ARM linux community have plans to
>> > support PSCI version 1.1 or not.
>> > PSCI_1_1 specification introduced support for SYSTEM_RESET2 command
>> > and this new command helps mobile devices to SYSTEM_WARM_RESET
>> > support. Rebooting devices with warm reboot helps to capture the
>> > snapshot of the ram contents for post-mortem analysis.
>>
>> I think, there is a recent discussion from Sudeep for the
>> SYSTEM_RESET2
>> support.
>> https://patchwork.kernel.org/patch/10884345/
>>
>
> This has landed in -next, and hopefully must appear in v5.2
>
>>
>> Hi Sudeep,
>>
>> I was going through your discussion in the below list -
>> https://lore.kernel.org/lkml/d73d3580-4ec1-a281-4585-5c776fc08c79@xilinx.com/
>>
>> There is no provision to set up reboot mode dynamically instead kernel
>> command line parameter.
>> Looking for options to reboot device with warm reboot option when
>> kernel
>> crashed.
>>
>> panic() --> emergency_restart() --> machine_emergency_restart() -->
>> machine_restart(NULL);
>>
>> 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.
<Sudeep> 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.

>
> 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?

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.

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

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