[PATCH] drm/i915/gt: debugfs: Evaluate forcewake usage within locks

[Tvrtko Ursulin]

On 10/06/2024 10:24, Nirmoy Das wrote:
> Hi Andi,
> 
> On 6/7/2024 4:51 PM, Andi Shyti wrote:
>> The forcewake count and domains listing is multi process critical
>> and the uncore provides a spinlock for such cases.
>>
>> Lock the forcewake evaluation section in the fw_domains_show()
>> debugfs interface.
>>
>> Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
> 
> Needs a Fixes tag, below seems to be correct one.
> 
> 
> Fixes: 9dd4b065446a ("drm/i915/gt: Move pm debug files into a gt aware 
> debugfs")
> 
> Cc: <stable at vger.kernel.org> # v5.6+
> 
> Reviewed-by: Nirmoy Das <nirmoy.das at intel.com>

What is the back story here and why would it need backporting? IGT cares 
about the atomic view of user_forcewake_count and individual domains or 
what?

Regards,

Tvrtko


> 
> Regards,
> 
> Nirmoy
> 
> 
>> ---
>>   drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c 
>> b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>> index 4fcba42cfe34..0437fd8217e0 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>> @@ -71,6 +71,8 @@ static int fw_domains_show(struct seq_file *m, void 
>> *data)
>>       struct intel_uncore_forcewake_domain *fw_domain;
>>       unsigned int tmp;
>> +    spin_lock_irq(&uncore->lock);
>> +
>>       seq_printf(m, "user.bypass_count = %u\n",
>>              uncore->user_forcewake_count);
>> @@ -79,6 +81,8 @@ static int fw_domains_show(struct seq_file *m, void 
>> *data)
>>                  intel_uncore_forcewake_domain_to_str(fw_domain->id),
>>                  READ_ONCE(fw_domain->wake_count));
>> +    spin_unlock_irq(&uncore->lock);
>> +
>>       return 0;
>>   }
>>   DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(fw_domains);