Re: [Intel-gfx] [PATCH v5 1/4] drm/i915/guc: Add fetch of hwconfig table

[Jordan Justen <jordan.l.justen@intel.com>]

John Harrison <john.c.harrison@intel.com> writes:

> On 2/22/2022 02:36, Jordan Justen wrote:
>> From: John Harrison <John.C.Harrison@Intel.com>
>>
>> Implement support for fetching the hardware description table from the
>> GuC. The call is made twice - once without a destination buffer to
>> query the size and then a second time to fill in the buffer.
>>
>> Note that the table is only available on ADL-P and later platforms.
>>
>> v5 (of Jordan's posting):
>>   * Various changes made by Jordan and recommended by Michal
>>     - Makefile ordering
>>     - Adjust "struct intel_guc_hwconfig hwconfig" comment
>>     - Set Copyright year to 2022 in intel_guc_hwconfig.c/.h
>>     - Drop inline from hwconfig_to_guc()
>>     - Replace hwconfig param with guc in __guc_action_get_hwconfig()
>>     - Move zero size check into guc_hwconfig_discover_size()
>>     - Change comment to say zero size offset/size is needed to get size
>>     - Add has_guc_hwconfig to devinfo and drop has_table()
>>     - Change drm_err to notice in __uc_init_hw() and use %pe
>>
>> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
>> Reviewed-by: Matthew Brost <matthew.brost@intel.com>
>> Acked-by: Jon Bloomfield <jon.bloomfield@intel.com>
>> Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
>> ---
>>   
>> +	ret = intel_guc_hwconfig_init(&guc->hwconfig);
>> +	if (ret)
>> +		drm_notice(&i915->drm, "Failed to retrieve hwconfig table: %pe\n",
> Why only drm_notice? As you are keen to point out, the UMDs won't work 
> if the table is not available. All the failure paths in your own 
> verification function are 'drm_err'. So why is it only a 'notice' if 
> there is no table at all?

This was requested by Michal in my v3 posting:

https://patchwork.freedesktop.org/patch/472936/?series=99787&rev=3

I don't think that it should be a failure for i915 if it is unable to
read the table, or if the table read is invalid. I think it should be up
to the UMD to react to the missing hwconfig however they think is
appropriate, but I would like the i915 to guarantee & document the
format returned to userspace to whatever extent is feasible.

As you point out there is a discrepancy, and I think I should be
consistent with whatever is used here in my "drm/i915/guc: Verify
hwconfig blob matches supported format" patch.

I guess I'd tend to agree with Michal that "maybe drm_notice since we
continue probe", but I would go along with either if you two want to
discuss further.

> Note that this function is called as part of the reset path. The reset 
> path is not allowed to allocate memory. The table is stored in a 
> dynamically allocated object. Hence the IGT test failure. The table 
> query has to be done elsewhere at driver init time only.

Thanks for clearing this up. I did notice on dg2 that gpu resets were
causing a re-read of the hwconfig from GuC, but it definitely was not
clear to me that there would be a connection to the IGT failure that you
pointed out.

>
>> +			   ERR_PTR(ret));
>> +
>>   	ret = guc_enable_communication(guc);
>>   	if (ret)
>>   		goto err_log_capture;
>> @@ -562,6 +567,8 @@ static void __uc_fini_hw(struct intel_uc *uc)
>>   	if (intel_uc_uses_guc_submission(uc))
>>   		intel_guc_submission_disable(guc);
>>   
>> +	intel_guc_hwconfig_fini(&guc->hwconfig);
>> +
>>   	__uc_sanitize(uc);
>>   }
>>   
>> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
>> index 76e590fcb903..1d31e35a5154 100644
>> --- a/drivers/gpu/drm/i915/i915_pci.c
>> +++ b/drivers/gpu/drm/i915/i915_pci.c
>> @@ -990,6 +990,7 @@ static const struct intel_device_info adl_p_info = {
>>   		BIT(RCS0) | BIT(BCS0) | BIT(VECS0) | BIT(VCS0) | BIT(VCS2),
>>   	.ppgtt_size = 48,
>>   	.dma_mask_size = 39,
>> +	.has_guc_hwconfig = 1,
> Who requested this change? It was previously done this way but the 
> instruction was that i915_pci.c is for hardware features only but that 
> this, as you seem extremely keen about pointing out at every 
> opportunity, is a software feature.

This was requested by Michal as well. I definitely agree it is a
software feature, but I was not aware that "i915_pci.c is for hardware
features only".

Michal, do you agree with this and returning to the previous method for
enabling the feature?

-Jordan