Re: [PATCH v3 2/4] drm/i915: Always set HUC_LOADING_AGENT_GUC bit in WOPCM offset register

["Michal Wajdeczko" <michal.wajdeczko@intel.com>]

On Mon, 16 Apr 2018 19:43:52 +0200, Yaodong Li <yaodong.li@intel.com>  
wrote:

> On 04/13/2018 07:26 PM, Michal Wajdeczko wrote:
>> On Tue, 10 Apr 2018 02:42:18 +0200, Jackie Li <yaodong.li@intel.com>  
>> wrote:
>>
>>> The enable_guc modparam is used to enable/disable GuC/HuC FW uploading
>>> dynamcially during i915 module loading. If WOPCM offset register was
>>   ^^^^
>> typo
>>
> D'oh! I really need a tool for this! Thanks, will fix it.
>>> locked
>>> without having HUC_LOADING_AGENT_GUC bit set to 1, the module reloading
>>> with both GuC and HuC FW will fail since we need to set this bit to 1  
>>> for
>>> HuC FW uploading.
>>>
>>> Since HUC_LOADING_AGENT_GUC bit has no impact on GuC FW uploading, this
>>> patch updates the register updating code to make sure the WOPCM offset
>>> register is always locked with HUC_LOADING_AGENT_GUC bit set to 1 which
>>> will guarantee successful uploading of both GuC and HuC FW. We will  
>>> further
>>> take care of the locked values in the following enhancement patch.
>>>
>>> Signed-off-by: Jackie Li <yaodong.li@intel.com>
>>> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
>>> Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
>>> Cc: Michal Winiarski <michal.winiarski@intel.com>
>>> Cc: John Spotswood <john.a.spotswood@intel.com>
>>> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/intel_wopcm.c | 8 +++-----
>>>  1 file changed, 3 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_wopcm.c  
>>> b/drivers/gpu/drm/i915/intel_wopcm.c
>>> index 74bf76f..b1c08ca 100644
>>> --- a/drivers/gpu/drm/i915/intel_wopcm.c
>>> +++ b/drivers/gpu/drm/i915/intel_wopcm.c
>>> @@ -238,8 +238,6 @@ static inline int write_and_verify(struct  
>>> drm_i915_private *dev_priv,
>>>  int intel_wopcm_init_hw(struct intel_wopcm *wopcm)
>>>  {
>>>      struct drm_i915_private *dev_priv = wopcm_to_i915(wopcm);
>>> -    u32 huc_agent;
>>> -    u32 mask;
>>>      int err;
>>>     if (!USES_GUC(dev_priv))
>>> @@ -255,10 +253,10 @@ int intel_wopcm_init_hw(struct intel_wopcm  
>>> *wopcm)
>>>      if (err)
>>>          goto err_out;
>>> -    huc_agent = USES_HUC(dev_priv) ? HUC_LOADING_AGENT_GUC : 0;
>>> -    mask = GUC_WOPCM_OFFSET_MASK | GUC_WOPCM_OFFSET_VALID | huc_agent;
>>>      err = write_and_verify(dev_priv, DMA_GUC_WOPCM_OFFSET,
>>> -                   wopcm->guc.base | huc_agent, mask,
>>> +                   wopcm->guc.base | HUC_LOADING_AGENT_GUC,
>>> +                   GUC_WOPCM_OFFSET_MASK | HUC_LOADING_AGENT_GUC |
>>> +                   GUC_WOPCM_OFFSET_VALID,
>>
>> while we can unconditionally set HUC_AGENT bit, there is no need to  
>> verify
>> it unless we are using HuC, so we can consider leaving old mask intact.
> The idea is to verify the written values are exactly we want, so I think  
> it better
> to keep doing it in this way.

Hmm, but then instead of being more flexible, you're unnecessary  
restricting
yourself to require HUC_AGENT bit, even if you don't need it - recall the
theoretical scenario with bad bios that already locked that register.

This seems to be little inconsistent with earlier patch where you try to
support much more different scenario (from no HuC fw to use HuC fw)

/m
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