Re: [Intel-gfx] [PATCH] drm/i915/huc: Fix error reported by I915_PARAM_HUC_STATUS

["Ye, Tony" <tony.ye@intel.com>]

On 1/27/2020 1:41 AM, Michal Wajdeczko wrote:
> On Thu, 23 Jan 2020 16:51:58 +0100, Chris Wilson 
> <chris@chris-wilson.co.uk> wrote:
> 
>> Quoting Michal Wajdeczko (2020-01-23 15:38:52)
>>> On Thu, 23 Jan 2020 16:02:17 +0100, Chris Wilson
>>> <chris@chris-wilson.co.uk> wrote:
>>>
>>> > Quoting Daniele Ceraolo Spurio (2020-01-22 23:52:33)
>>> >>
>>> >>
>>> >> On 1/22/20 11:48 AM, Michal Wajdeczko wrote:
>>> >> >  From commit 84b1ca2f0e68 ("drm/i915/uc: prefer intel_gt over i915
>>> >> > in GuC/HuC paths") we stopped using HUC_STATUS error -ENODEV only
>>> >> > to indicate lack of HuC hardware and we started to use this error
>>> >> > also for all other cases when HuC was not in use or supported.
>>> >> >
>>> >> > Fix that by relying again on HAS_GT_UC macro, since currently
>>> >> > used function intel_huc_is_supported() is based on HuC firmware
>>> >> > support which could be unsupported also due to force disabled
>>> >> > GuC firmware.
>>> >> >
>>> >> > Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
>>> >> > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>>> >> > Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
>>> >> > Cc: Tony Ye <tony.ye@intel.com>
>>> >>
>>> >> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>>> >
>>> > Once upon a time did you (Michal) not argue we should indicate the 
>>> lack
>>> > of firmware in the error code? Something like
>>> >
>>> > if (!HAS_GT_UC(gt->i915))
>>> >       return -ENODEV;
>>> >
>>> > if (!intel_huc_is_supported(huc))
>>> >       return -ENOEXEC;
>>>
>>> Yes, we discussed this here [1] together with [2] but we didn't
>>> conclude our discussion due to different opinions on how represent
>>> some states, in particular "manually disabled" state.
>>>
>>> In this patch I just wanted to restore old notation.
>>>
>>> But we can start new discussion, here is summary:
>>>
>>> ------------------+----------+----------+----------
>>>   HuC state        | today*   | option A | option B
>>> ------------------+----------+----------+----------
>>> no HuC hardware   | -ENODEV  | -ENODEV  | -ENODEV
>>> GuC fw disabled   |   0      |     0    | -EOPNOTSUPP
>>> HuC fw disabled   |   0      |     0    | -EOPNOTSUPP
>>> HuC fw missing    |   0      | -ENOPKG  | -ENOEXEC
>>> HuC fw error      |   0      | -ENOEXEC | -ENOEXEC
>>> HuC fw fail       |   0      | -EACCES  |    0
>>> HuC authenticated |   1      |     1    |    1
>>> ------------------+----------+----------+----------
>>
>> By fw fail, you mean we loaded the firmware (to our knowledge)
>> correctly, but HUC_STATUS is not reported as valid?
>>
>> If so, I support option B. I like the idea of saying
>> "no HuC" (machine too old)
>> "no firmware" (user action, or lack thereof)
>> 0 (fw unhappy)
>> 1 (fw reports success)
>>
>> In between states for failures in fw loading? Not so sure. But I can see
>> the nicety in distinguishing between lack of firmware and some random
>> failure in loading the firmware (the former being user action required
>> to rectify, command line parameter whatever and the latter being the
>> firmware file is either invalid or a stray neutrino prevented loading).
>>
>> Imo the error messages should be about why we cannot probe/trust the
>> HUC_STATUS register. If everything is setup correctly then the returned
>> value should be from reading the register. I dislike only returning 1 if
>> supported, and converting a valid read of 0 into another error.
>>
>> So Option B :)
> 
> But I'm not sure that option B is consistent in error reporting, as
> "fw unhappy" is definitely an serious error but is represented as plain
> non-error "0" status, while "fw disabled" (user action) is treated as error
> 
> ------------------+----------
>    HuC state       | option B
> ------------------+----------
> no HuC hardware   | -ENODEV
> GuC fw disabled   | -EOPNOTSUPP -> user decision, why error?
> HuC fw disabled   | -EOPNOTSUPP -> user decision, why error?
> HuC fw missing    | -ENOEXEC
> HuC fw error      | -ENOEXEC
> HuC fw fail       |    0        -> unlikely, but still fw/hw error
> HuC authenticated |    1
> ------------------+----------
> 
> On other hand, option A treats all error conditions as errors, leaving
> status codes only for normal operations: disabled(0)/authenticated(1):
> 
> ------------------+----------
>    HuC state       | option A
> ------------------+----------
> no HuC hardware   | -ENODEV  -> you shouldn't ask
> GuC fw disabled   |     0    -> user decision, not an error
> HuC fw disabled   |     0    -> user decision, not an error
> HuC fw missing    | -ENOPKG  -> fw not installed correctly
> HuC fw error      | -ENOEXEC -> bad/wrong fw
> HuC fw fail       | -EACCES  -> fw/hw error
> HuC authenticated |     1
> ------------------+----------

Vote for Option A.

Regards,
Tony

> 
> But since I'm not an active HuC user, will leave final decision to others.
> 
> /Michal
> 
> 
>>
>>> Note that all above should be compatible with media driver,
>>> which explicitly looks for no error and value 1
>>
>> Cool.
>> -Chris
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