[Intel-gfx] [PATCH] drm/i915: There is only one fault register from GEN8 onwards

[Michel Thierry]

On 11/10/2017 12:51 PM, Chris Wilson wrote:
> Quoting Michel Thierry (2017-11-10 19:01:16)
>> Until Haswell/Baytrail, the hardware used to have a per engine fault
>> register (e.g. 0x4094 - render fault register, 0x4194 - media fault
>> register and so on). But since Broadwell, all these registers were
>> combined into a singe one and the engine id stored in bits 14:12.
>>
>> Not only we should not been reading (and writing to) registers that do
>> not exist, in platforms with VCS2 (SKL), the address that would belong
>> this engine (0x4494, VCS2_HW = 4) is already assigned to other register.
>>
>> References: IHD-OS-BDW-Vol 2c-11.15, page 75.
>> References: IHD-OS-SKL-Vol 2c-05.16, page 350.
>> Signed-off-by: Michel Thierry <michel.thierry at intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gem_gtt.c   | 38 ++++++++++++++++++++++++++++++-----
>>   drivers/gpu/drm/i915/i915_gpu_error.c |  8 +++++---
>>   drivers/gpu/drm/i915/i915_reg.h       |  2 ++
>>   3 files changed, 40 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index 1e40eeb31f9d..66a907330ad2 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -2256,16 +2256,13 @@ static bool needs_idle_maps(struct drm_i915_private *dev_priv)
>>          return IS_GEN5(dev_priv) && IS_MOBILE(dev_priv) && intel_vtd_active();
>>   }
>>   
>> -void i915_check_and_clear_faults(struct drm_i915_private *dev_priv)
>> +void __check_and_clear_faults(struct drm_i915_private *dev_priv)
> 
> I am amazed that -Wextra doesn't complain. Try with sparse.
>

Hmm, no they didn't... gen6_check_and_clear_faults and 
gen8_check_and_clear_faults are less controversial.

> There's an old thread where this was raised and how we are not clearing
> the faults early enough.

Ah, I found that thread [1], and as you said there, right now the 
for_each_engine is a nop (with this patch at least gen8+ would do the 
right thing).

Since gen6/gen7 engines are well known and can't change, do we really 
need for_each_engine?

[1] https://patchwork.freedesktop.org/patch/101331/