[Intel-gfx] [PATCH v2] drm/i915/gt: prevent forcewake releases during BAR resize

[Andrzej Hajda]

On 08.03.2023 18:29, Das, Nirmoy wrote:
> 
> On 3/8/2023 2:36 PM, Andrzej Hajda wrote:
>> Tests on DG2 machines show that releasing forcewakes during BAR resize
>> results later in forcewake ack timeouts.
> Do we have a fdo/issues url for that? Having that as References would be 
> nice.

The patch is result of issue reported internally, but...grepping 
bugtracker I've found potential candidates:

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6530
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7853

Maybe it would be good to add them on merge.
Anyway thx for a-b.

Regards
Andrzej

>>   Since forcewakes can be realeased
>> asynchronously the simplest way to prevent it is to get all forcewakes
>> for duration of BAR resizing.
>>
>> v2: hold rpm as well during resizing (Rodrigo)
>>
>> Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
> 
> 
> Acked-by: Nirmoy Das <nirmoy.das at intel.com>
> 
> 
>> ---
>> Please ignore resend of v1, my mistake.
>>
>> Regards
>> Andrzej
>> ---
>>   drivers/gpu/drm/i915/gt/intel_region_lmem.c | 25 +++++++++++++++------
>>   1 file changed, 18 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_region_lmem.c 
>> b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
>> index 89fdfc67f8d1e0..2a3217e2890fc7 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_region_lmem.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
>> @@ -54,6 +54,7 @@ static void i915_resize_lmem_bar(struct 
>> drm_i915_private *i915, resource_size_t
>>       struct resource *root_res;
>>       resource_size_t rebar_size;
>>       resource_size_t current_size;
>> +    intel_wakeref_t wakeref;
>>       u32 pci_cmd;
>>       int i;
>> @@ -102,15 +103,25 @@ static void i915_resize_lmem_bar(struct 
>> drm_i915_private *i915, resource_size_t
>>           return;
>>       }
>> -    /* First disable PCI memory decoding references */
>> -    pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
>> -    pci_write_config_dword(pdev, PCI_COMMAND,
>> -                   pci_cmd & ~PCI_COMMAND_MEMORY);
>> +    /*
>> +     * Releasing forcewake during BAR resizing results in later 
>> forcewake
>> +     * ack timeouts and former can happen any time - it is asynchronous.
>> +     * Grabbing all forcewakes prevents it.
>> +     */
>> +    with_intel_runtime_pm(i915->uncore.rpm, wakeref) {
>> +        intel_uncore_forcewake_get(&i915->uncore, FORCEWAKE_ALL);
>> -    _resize_bar(i915, GEN12_LMEM_BAR, rebar_size);
>> +        /* First disable PCI memory decoding references */
>> +        pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
>> +        pci_write_config_dword(pdev, PCI_COMMAND,
>> +                       pci_cmd & ~PCI_COMMAND_MEMORY);
>> -    pci_assign_unassigned_bus_resources(pdev->bus);
>> -    pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
>> +        _resize_bar(i915, GEN12_LMEM_BAR, rebar_size);
>> +
>> +        pci_assign_unassigned_bus_resources(pdev->bus);
>> +        pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
>> +        intel_uncore_forcewake_put(&i915->uncore, FORCEWAKE_ALL);
>> +    }
>>   }
>>   #else
>>   static void i915_resize_lmem_bar(struct drm_i915_private *i915, 
>> resource_size_t lmem_size) {}