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

[Michal Wajdeczko]

On Thu, 23 Jan 2020 16:51:58 +0100, Chris Wilson  
<chris at 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 at 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 at intel.com>
>> >> > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
>> >> > Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
>> >> > Cc: Tony Ye <tony.ye at intel.com>
>> >>
>> >> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at 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
------------------+----------

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