Re: [PATCH 4/5] drm/i915: Let number of workarounds more clear

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 26 Sep 2014, Mika Kuoppala <mika.kuoppala@linux.intel.com> wrote:
> Rodrigo Vivi <rodrigo.vivi@intel.com> writes:
>
>> This helps when including or removing cs workarounds.
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_ringbuffer.c | 16 ++++++++++++----
>>  1 file changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> index 7c3d17a..39fbea6 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> @@ -694,6 +694,7 @@ static int bdw_init_workarounds(struct intel_engine_cs *ring)
>>  	int ret;
>>  	struct drm_device *dev = ring->dev;
>>  	struct drm_i915_private *dev_priv = dev->dev_private;
>> +	int wa_amount;
>>  
>>  	/*
>>  	 * workarounds applied in this fn are part of register state context,
>> @@ -704,10 +705,11 @@ static int bdw_init_workarounds(struct intel_engine_cs *ring)
>>  	memset(dev_priv->intel_wa_regs, 0, sizeof(dev_priv->intel_wa_regs));
>>  
>>  	/*
>> -	 * update the number of dwords required based on the
>> -	 * actual number of workarounds applied
>> +	 * update the number of workarounds when adding or removing was
>> +	 * in order the have propper dwords
>>  	 */
>> -	ret = intel_ring_begin(ring, 24);
>> +	wa_amount = 8;
>> +	ret = intel_ring_begin(ring, 3 * wa_amount);
>>  	if (ret)
>>  		return ret;
>>  
>
> I have a bit mixed feelings with this patch as I have tripped
> around here myself recently.
>
> I think we should just drop this patch and use:
> ret = intel_ring_begin(ring, 3 * <amount>) on the subsequent
> patches that modify the amount.
>
> This way the intel_ring_begin will always be the one that
> shows in a diff. And raises alarm if it doesnt. We don't want
> this to be too transparent and looking too easy for the next reader.
> As the reviewer is the only and last line of defense ensuring
> symmetry between intel_ring_begin and amount of emits.

Considering intel_ring_emit_wa() adds all the needed information to
dev_priv->intel_wa_regs and dev_priv->num_wa_regs anyway, we could
trivially split this into constructing dev_priv->intel_wa_regs first,
and doing intel_ring_begin() and the intel_ring_emit()s next, and not
worry about this again.

BR,
Jani.

>
> -Mika
>
>> @@ -775,6 +777,7 @@ static int chv_init_workarounds(struct intel_engine_cs *ring)
>>  	int ret;
>>  	struct drm_device *dev = ring->dev;
>>  	struct drm_i915_private *dev_priv = dev->dev_private;
>> +	int wa_amount;
>>  
>>  	/*
>>  	 * workarounds applied in this fn are part of register state context,
>> @@ -784,7 +787,12 @@ static int chv_init_workarounds(struct intel_engine_cs *ring)
>>  	dev_priv->num_wa_regs = 0;
>>  	memset(dev_priv->intel_wa_regs, 0, sizeof(dev_priv->intel_wa_regs));
>>  
>> -	ret = intel_ring_begin(ring, 12);
>> +	/*
>> +	 * update the number of workarounds when adding or removing was
>> +	 * in order the have propper dwords
>> +	 */
>> +	wa_amount = 4;
>> +	ret = intel_ring_begin(ring, 3 * wa_amount);
>>  	if (ret)
>>  		return ret;
>>  
>> -- 
>> 1.9.3
>>
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-- 
Jani Nikula, Intel Open Source Technology Center