Subject: Re: [PATCH v10 24/27] drivers: firmware: psci: Support CPU hotplug for the hierarchical model

From: Lina Iyer <[email-masked]>
Date: Thu, 29 Nov 2018 15:31:30 -0700

Hi Ulf,

On Thu, Nov 29 2018 at 10:50 -0700, Ulf Hansson wrote:
>When the hierarchical CPU topology is used and when a CPU has been put
>offline (hotplug), that same CPU prevents its PM domain and thus also
>potential master PM domains, from being powered off. This is because genpd
>observes the CPU's struct device to remain being active from a runtime PM
>point of view.
>
>To deal with this, let's decrease the runtime PM usage count by calling
>pm_runtime_put_sync_suspend() of the CPU's struct device when putting it
>offline. Consequentially, we must then increase the runtime PM usage for
>the CPU, while putting it online again.
>
>Signed-off-by: Ulf Hansson <[email-masked]>
>---
>
>Changes in v10:
>	- Make it work when the hierarchical CPU topology is used, which may be
>	  used both for OSI and PC mode.
>	- Rework the code to prevent "BUG: sleeping function called from
>	  invalid context".
>---
> drivers/firmware/psci/psci.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
>diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
>index b03bccce0a5d..f62c4963eb62 100644
>--- a/drivers/firmware/psci/psci.c
>+++ b/drivers/firmware/psci/psci.c
>@@ -15,6 +15,7 @@
>
> #include <linux/acpi.h>
> #include <linux/arm-smccc.h>
>+#include <linux/cpu.h>
> #include <linux/cpuidle.h>
> #include <linux/errno.h>
> #include <linux/linkage.h>
>@@ -199,9 +200,20 @@ static int psci_cpu_suspend(u32 state, unsigned long entry_point)
>
> static int psci_cpu_off(u32 state)
> {
>+	struct device *dev;
> 	int err;
> 	u32 fn;
>
>+	/*
>+	 * When the hierarchical CPU topology is used, decrease the runtime PM
>+	 * usage count for the current CPU, as to allow other parts in the
>+	 * topology to enter low power states.
>+	 */
>+	if (psci_dt_topology) {
>+		dev = get_cpu_device(smp_processor_id());
>+		pm_runtime_put_sync_suspend(dev);
>+	}
>+
> 	fn = psci_function_id[PSCI_FN_CPU_OFF];
> 	err = invoke_psci_fn(fn, state, 0, 0);
> 	return psci_to_linux_errno(err);
>@@ -209,6 +221,7 @@ static int psci_cpu_off(u32 state)
>
> static int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
> {
>+	struct device *dev;
> 	int err;
> 	u32 fn;
>
>@@ -216,6 +229,13 @@ static int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
> 	err = invoke_psci_fn(fn, cpuid, entry_point, 0);
> 	/* Clear the domain state to start fresh. */
> 	psci_set_domain_state(0);
>+
>+	/* Increase runtime PM usage count if the hierarchical CPU toplogy. */
>+	if (!err && psci_dt_topology) {
>+		dev = get_cpu_device(cpuid);
>+		pm_runtime_get_sync(dev);

I booted with a single CPU on my SDM845 device and when I tried to
online CPU1 and I see a crash.

# echo 1 > /sys/devices/system/cpu/cpu1/online                                                 
                                                     
[   86.339204] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000188       
[   86.340195] Detected VIPT I-cache on CPU1                                                              
[   86.348075] Mem abort info:                                                                            
[   86.348092] GICv3: CPU1: found redistributor 100 region 0:0x0000000017a80000                           
[   86.352125]   ESR = 0x96000006                                                                         
[   86.352194] CPU1: Booted secondary processor 0x0000000100 [0x517f803c]                                 
[   86.354956]   Exception class = DABT (current EL), IL = 32 bits                                        
[   86.377700]   SET = 0, FnV = 0                                                                         
[   86.380788]   EA = 0, S1PTW = 0                                                                        
[   86.383967] Data abort info:                                                                           
[   86.386882]   ISV = 0, ISS = 0x00000006                                                                
[   86.390760]   CM = 0, WnR = 0                                                                          
[   86.393755] user pgtable: 4k pages, 48-bit VAs, pgdp = (____ptrval____)                                
[   86.400430] [0000000000000188] pgd=00000001f5233003, pud=00000001f5234003, pmd=0000000000000000        
[   86.409203] Internal error: Oops: 96000006 [#1] PREEMPT SMP                                            
[   86.414824] Modules linked in:                                                                         
[   86.417915] CPU: 0 PID: 1533 Comm: sh Not tainted 4.20.0-rc3-30359-gff2e21952bd5 #782                  
[   86.425807] Hardware name: Qualcomm Technologies, Inc. SDM845 MTP (DT)                                 
[   86.432387] pstate: 80400005 (Nzcv daif +PAN -UAO)                                                     
[   86.437233] pc : __pm_runtime_resume+0x20/0x74                                                         
[   86.441720] lr : psci_cpu_on+0x84/0x90                                                                 
[   86.445498] sp : ffff00000db43a10                                                                      
[   86.448842] x29: ffff00000db43a10 x28: ffff80017562b500                                                
[   86.454200] x27: ffff000009159000 x26: 0000000000000055                                                
[   86.459556] x25: 0000000000000000 x24: ffff0000092c4bc8                                                
[   86.464913] x23: ffff000008fb8000 x22: ffff00000916a000                                                
[   86.470269] x21: 0000000000000100 x20: ffff000009314190                                                
[   86.475625] x19: 0000000000000000 x18: 0000000000000000                                                
[   86.480979] x17: 0000000000000000 x16: 0000000000000000                                                
[   86.486334] x15: 0000000000000000 x14: ffff000009162600                                                
[   86.491690] x13: 0000000000000300 x12: 0000000000000010                                                
[   86.497047] x11: ffffffffffffffff x10: ffffffffffffffff                                                
[   86.502399] x9 : 0000000000000001 x8 : 0000000000000000                                                
[   86.507753] x7 : 0000000000000000 x6 : 0000000000000000                                                
[   86.513108] x5 : 0000000000000000 x4 : 0000000000000000                                                
[   86.518463] x3 : 0000000000000188 x2 : 0000800174385000                                                
[   86.523820] x1 : 0000000000000004 x0 : 0000000000000000                                                
[   86.529175] Process sh (pid: 1533, stack limit = 0x(____ptrval____))                                   
[   86.535585] Call trace:                                                                                
[   86.538063]  __pm_runtime_resume+0x20/0x74                                                             
[   86.542197]  psci_cpu_on+0x84/0x90                                                                     
[   86.545639]  cpu_psci_cpu_boot+0x3c/0x6c                                                               
[   86.549593]  __cpu_up+0x68/0x210                                                                       
[   86.552852]  bringup_cpu+0x30/0xe0                                                                     
[   86.556293]  cpuhp_invoke_callback+0x84/0x1e0                                                          
[   86.560689]  _cpu_up+0xe0/0x1d0                                                                        
[   86.563862]  do_cpu_up+0x90/0xb0                                                                       
[   86.567118]  cpu_up+0x10/0x18                                                                          
[   86.570113]  cpu_subsys_online+0x44/0x98                                                               
[   86.574079]  device_online+0x68/0xac                                                                   
[   86.577685]  online_store+0xa8/0xb4                                                                    
[   86.581202]  dev_attr_store+0x18/0x28                                                                  
[   86.584908]  sysfs_kf_write+0x40/0x48                                                                  
[   86.588606]  kernfs_fop_write+0xcc/0x1cc                                                               
[   86.592563]  __vfs_write+0x40/0x16c                                                                    
[   86.596078]  vfs_write+0xa8/0x1a0                                                                      
[   86.599424]  ksys_write+0x58/0xbc                                                                      
[   86.602768]  __arm64_sys_write+0x18/0x20                                                               
[   86.606733]  el0_svc_common+0x94/0xf0                                                                  
[   86.610433]  el0_svc_handler+0x24/0x80                                                                 
[   86.614215]  el0_svc+0x8/0x7c0                                                                         
[   86.617300] Code: aa0003f3 361000e1 91062263 f9800071 (885f7c60)                                       
[   86.623447] ---[ end trace 4573c3c0e0761290 ]---                                                       

>+	}
>+
> 	return psci_to_linux_errno(err);
> }
>
>-- 
>2.17.1
>

Thanks,
Lina

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