Re: [PATCH v2] powerpc/kernel/sysfs: Export ldbar spr to sysfs

Hi mpe,


On Wednesday 01 November 2017 06:20 AM, Michael Ellerman wrote:

Anju T Sudhakar [off-list ref] writes:

quoted

Add ldbar spr to sysfs. The spr will hold thread level In-Memory Collection (IMC)
counter configuration data.

This is missing any justification for why we would want to expose this,
and in particular why we would make it *writable*.

cheers

Thank you for reviewing the patch.

LDBAR, holds the thread-level counter configuration. Exposing this will help
us to understand  the current status of thread-level counters in the system.
Primarily, Bit 0 of ldbar tells whether the counters are enabled or not.
And bit 1  tells the mode (if 0-Accumulation Mode/if 1-Trace Mode).

But regarding the permission, you are right. On a reassessment I think 
that the permission
should be read only, because it is possible that we may write an 
incorrect value to the ldbar, that is wrong.
So I will change the permission here.



Thanks,
Anju

quoted

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 4437c70..f8caee0 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c

@@ -485,6 +485,7 @@ SYSFS_PMCSETUP(mmcra, SPRN_MMCRA);
  SYSFS_SPRSETUP(purr, SPRN_PURR);
  SYSFS_SPRSETUP(spurr, SPRN_SPURR);
  SYSFS_SPRSETUP(pir, SPRN_PIR);
+SYSFS_SPRSETUP(ldbar, SPRN_LDBAR);
  
  /*
    Lets only enable read for phyp resources and

@@ -492,6 +493,7 @@ SYSFS_SPRSETUP(pir, SPRN_PIR);
    Lets be conservative and default to pseries.
  */
  static DEVICE_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
+static DEVICE_ATTR(ldbar, 0600, show_ldbar, store_ldbar);
  static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
  static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
  static DEVICE_ATTR(pir, 0400, show_pir, NULL);

@@ -757,6 +759,9 @@ static int register_cpu_online(unsigned int cpu)
  			device_create_file(s, &pmc_attrs[i]);
  
  #ifdef CONFIG_PPC64
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		device_create_file(s, &dev_attr_ldbar);
+
  	if (cpu_has_feature(CPU_FTR_MMCRA))
  		device_create_file(s, &dev_attr_mmcra);
  

@@ -842,6 +847,9 @@ static int unregister_cpu_online(unsigned int cpu)
  			device_remove_file(s, &pmc_attrs[i]);
  
  #ifdef CONFIG_PPC64
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		device_remove_file(s, &dev_attr_ldbar);
+
  	if (cpu_has_feature(CPU_FTR_MMCRA))
  		device_remove_file(s, &dev_attr_mmcra);
  

-- 
2.7.4