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. > 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