[Intel-gfx] [PATCH v2] drm/i915/huc: Don't try to check HuC status if it's not loaded
Ye, Tony
tony.ye at intel.com
Wed May 22 11:32:41 UTC 2019
On 5/21/2019 7:08 PM, Michal Wajdeczko wrote:
> On Tue, 21 May 2019 13:04:12 +0200, Ye, Tony <tony.ye at intel.com> wrote:
>
>> There are two users of I915_PARAM_HUC_STATUS, the intel-media driver
>> and the legacy intel-vaapi-driver.
>>
>> Both drivers check the return value like this:
>>
>> has_huc = !! ret_value;
>>
>> So the ABI change will break the existing stack because negative
>> values are treated as 1, won't it?
>
> No, since negative errors returned by i915 intel_huc_check_status()
> function
> will be only used to indicate ioctl() call failure and then stored in
> errno.
> Note that your "ret_value" will be modified only when ioctl is
> successful.
>
> Michal
Yeah, you are right.
>
>>
>> On 5/20/2019 8:16 PM, Michal Wajdeczko wrote:
>>
>>> On Mon, 20 May 2019 12:44:43 +0200, Chris Wilson
>>> <chris at chris-wilson.co.uk> wrote:
>>>
>>>> Quoting Michal Wajdeczko (2019-05-20 11:24:37)
>>>>> On Mon, 20 May 2019 11:35:26 +0200, Chris Wilson
>>>>> <chris at chris-wilson.co.uk> wrote:
>>>>>
>>>>> > Quoting Michal Wajdeczko (2019-05-19 22:50:43)
>>>>> >> If we never attempted to load HuC firmware, or we already wedged
>>>>> >> or reset GuC/HuC, then there is no reason to wake up the device
>>>>> >> to check one bit in the register that will be for sure cleared.
>>>>> >>
>>>>> >> v2: check if HuC was enabled; subtle change in ABI
>>>>> >> reuse hus_is_load helper
>>>>> >>
>>>>> >> Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>>> >> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
>>>>> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>>>>> >> Cc: Tony Ye <tony.ye at intel.com>
>>>>> >> ---
>>>>> >> drivers/gpu/drm/i915/intel_huc.c | 20 ++++++++++++--------
>>>>> >> drivers/gpu/drm/i915/intel_huc.h | 5 +++++
>>>>> >> 2 files changed, 17 insertions(+), 8 deletions(-)
>>>>> >>
>>>>> >> diff --git a/drivers/gpu/drm/i915/intel_huc.c
>>>>> >> b/drivers/gpu/drm/i915/intel_huc.c
>>>>> >> index 1ff1fb015e58..bfdebec1cfc8 100644
>>>>> >> --- a/drivers/gpu/drm/i915/intel_huc.c
>>>>> >> +++ b/drivers/gpu/drm/i915/intel_huc.c
>>>>> >> @@ -113,7 +113,7 @@ int intel_huc_auth(struct intel_huc *huc)
>>>>> >> u32 status;
>>>>> >> int ret;
>>>>> >>
>>>>> >> - if (huc->fw.load_status != INTEL_UC_FIRMWARE_SUCCESS)
>>>>> >> + if (!intel_huc_is_loaded(huc))
>>>>> >> return -ENOEXEC;
>>>>> >>
>>>>> >> ret = intel_guc_auth_huc(guc,
>>>>> >> @@ -150,21 +150,25 @@ int intel_huc_auth(struct intel_huc *huc)
>>>>> >> * This function reads status register to verify if HuC
>>>>> >> * firmware was successfully loaded.
>>>>> >> *
>>>>> >> - * Returns: 1 if HuC firmware is loaded and verified,
>>>>> >> - * 0 if HuC firmware is not loaded and -ENODEV if HuC
>>>>> >> - * is not present on this platform.
>>>>> >> + * Returns: 1 if HuC firmware is loaded and verified, 0 if HuC
>>>>> >> firmware is not
>>>>> >> + * enabled, -ENOPKG if HuC firmware is not loaded and -ENODEV
>>>>> if HuC
>>>>> >> is not
>>>>> >> + * present on this platform.
>>>>> >> */
>>>>> >> int intel_huc_check_status(struct intel_huc *huc)
>>>>> >> {
>>>>> >> struct drm_i915_private *dev_priv = huc_to_i915(huc);
>>>>> >> intel_wakeref_t wakeref;
>>>>> >> - bool status = false;
>>>>> >> + bool verified = false;
>>>>> >>
>>>>> >> if (!HAS_HUC(dev_priv))
>>>>> >> return -ENODEV;
>>>>> >>
>>>>> >> - with_intel_runtime_pm(dev_priv, wakeref)
>>>>> >> - status = I915_READ(HUC_STATUS2) & HUC_FW_VERIFIED;
>>>>> >> + if (!USES_HUC(dev_priv))
>>>>> >> + return 0;
>>>>> >
>>>>> > Hmm, EOPNOTSUPP here for the user disabled case?
>>>>>
>>>>> I'm not sure that user disabled case shall be reported as error,
>>>>> since it perfectly fits into legacy ABI 0="not loaded".
>>>>> The only small change is that now 0="not loaded (not enabled by
>>>>> user)"
>>>>
>>>> The only requirement for the intel-media driver seems to
>>>> "HUC_STATUS > 0".
>>>> That's our only user, so I think we have the liberty to redefine
>>>> <=0 as
>>>> befits error reporting.
>>>>
>>>>>
>>>>> >
>>>>> > Then
>>>>> >
>>>>> > if (!intel_huc_is_loaded(huc))
>>>>> > return -ENOPKG;
>>>>> >
>>>>> > bool verified = false;
>>>>> > with_intel_runtime_pm(dev_priv, wakeref)
>>>>> > verified = I915_READ(HUC_STATUS2) & HUC_FW_VERIFIED;
>>>>> > return verified.
>>>>> >
>>>>> > That keeps it a bit flatter with the special casing separate and
>>>>> the 0/1
>>>>> > result as given by the register status. Then if negative, we
>>>>> know one of
>>>>> > the preconditions for using HuC is not available, and if 0
>>>>> something went
>>>>> > wrong in mmio setup.
>>>>> >
>>>>> > Does that make sense?
>>>>>
>>>>> IMHO, if something went wrong it is better to report it as error
>>>>> rather
>>>>> then weak 0 status. Compare:
>>>>
>>>> I disagree, <0 is the weak case. 0 is the HW reports something went
>>>> wrong (and only that). 1 is the HW reports all went well.
>>>
>>> But I was assuming that we're defining ABI here, not simply exposing
>>> unified
>>> register value. Since we want 1 to report all ok, and we can fail
>>> for many
>>> reasons (no hw, no fw blob, wrong fw, bad signature, ...) we should
>>> at least
>>> try to match all these failures into error code (today just ENOPKG,
>>> but later
>>> we can extend into ENOEXEC=bad fw, ENOSPC=can't fit into WOPCM, ...).
>>>
>>> On other hand, at least for me, user decision to disable HuC should not
>>> be treated the same way as other real failures, so 0 seems like
>>> perfect match.
>>>
>>> Then we'll have: 1 = enabled, 0 = disabled, <0 = problem
>>>
>>>>
>>>> If we have more ways we can report the HW went wrong, sure expand that
>>>> into extra error codes, but I don't see that. And if it's in the regs,
>>>> why are not exporting them via reg_read_ioctl?
>>>>
>>>>> +---------------+-------+-------+-------+
>>>>> no hardware -ENODEV -ENODEV -ENODEV
>>>>> fw disabled 0 0 -ENOTSUP
>>>>> fw not loaded 0 -ENOPKG -ENOPKG
>>>>> fw not verified* 0 -ENOPKG 0
>>>>> fw verified* 1 1 1
>>>>> +---------------+-------+-------+-------+
>>>>> *) registry access
>>>>>
>>>>> Note that in your case, fw verification problem can be reported both
>>>>> as -ENOPKG or as 0 (former when verification fails at load time,
>>>>> latter
>>>>> as result of runtime reg read). Very likely we will never see 0 at
>>>>> all,
>>>>> since probably that can't change once fw was verified at load time.
>>>>
>>>> I see more distinction for ENODEV/ENOTSUP/ENOPKG/0/1. I am not getting
>>>> your point that we have conflation here, as to me it looks more
>>>
>>> Note that we are verifying HuC firmware right after it was loaded into
>>> hardware using exactly the same register as here (see intel_huc_auth),
>>> and if this fails we immediately change fw status to FAIL, so we never
>>> go beyond huc_is_loaded point.
>>>
>>> Assuming that once fw is verified it can't fail (to be verified later)
>>> then your codes will be only ENODEV/ENOTSUP/ENOPKG/1 (no 0 value)
>>>
>>>> distinct, and it is clear when we report the value as given by the
>>>> register and when we give an interpreted value for a driver error.
>>>
>>> Note that your initial idea was to reuse driver maintained fw status
>>> instead of waking up device just to check register again (we don't do
>>> that now as we need someone to confirm/verify that we can really skip
>>> reg read). Use 0/1 for ABI as register values does not fit here, imho.
>>>
>>> There is also a risk that we will report some known failures as <0
>>> error codes, while other, captured by hw as just 0.
>>>
>>>>
>>>>> That might be viewed as undesired ABI change.
>>>>
>>>> grep says it is fine, so I'm happy that no one else cares (as can be
>>>> seen by the lack of igt, no one has looked hard enough into how to
>>>> distinguish the API failures ;)
From UMD perspective, when HuC is not working as expected, usually we
look into the kernel log and i915_huc_load_status debugfs to find out
why it's not working. It will be helpful to know the reason of the
failure from the error code. The typically failures we encountered are
"HuC FW not loaded (FW not built into initramfs)" and "HuC FW
authentication failed".
And it looks clearer to me if we can define 0 as "disabled by user" to
distinguish it from other errors like ENODEV, ENOPKG and "not
authenticated".
Regards, --Tony
>>>
>>> it's always hard to come out from gray area into solid spec ;)
>>>
>>>> -Chris
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