Re: [Mesa-dev] [PATCH] intel: Fix stencil buffer to be W tiled

[Chad Versace <chad@chad-versace.us>]

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On 07/18/2011 08:57 AM, Eric Anholt wrote:
> On Mon, 18 Jul 2011 00:55:03 -0700, Chad Versace <chad@chad-versace.us> wrote:
>> diff --git a/src/mesa/drivers/dri/intel/intel_fbo.c b/src/mesa/drivers/dri/intel/intel_fbo.c
>> index 1669af2..507cc33 100644
>> --- a/src/mesa/drivers/dri/intel/intel_fbo.c
>> +++ b/src/mesa/drivers/dri/intel/intel_fbo.c
>> @@ -173,6 +173,9 @@ intel_alloc_renderbuffer_storage(struct gl_context * ctx, struct gl_renderbuffer
>>  
>>     if (irb->Base.Format == MESA_FORMAT_S8) {
>>        /*
>> +       * The stencil buffer is W tiled. However, we request from the kernel a
>> +       * non-tiled buffer because the GTT is incapable of W fencing.
>> +       *
>>         * The stencil buffer has quirky pitch requirements.  From Vol 2a,
>>         * 11.5.6.2.1 3DSTATE_STENCIL_BUFFER, field "Surface Pitch":
>>         *    The pitch must be set to 2x the value computed based on width, as
>> @@ -180,14 +183,14 @@ intel_alloc_renderbuffer_storage(struct gl_context * ctx, struct gl_renderbuffer
>>         * To accomplish this, we resort to the nasty hack of doubling the drm
>>         * region's cpp and halving its height.
>>         *
>> -       * If we neglect to double the pitch, then drm_intel_gem_bo_map_gtt()
>> -       * maps the memory incorrectly.
>> +       * If we neglect to double the pitch, then render corruption occurs.
>>         */
>>        irb->region = intel_region_alloc(intel->intelScreen,
>> -				       I915_TILING_Y,
>> +				       I915_TILING_NONE,
>>  				       cpp * 2,
>> -				       width,
>> -				       height / 2,
>> +				       ALIGN(width, 64),
>> +				       /* XXX: Maybe align to 128? */
>> +				       ALIGN(height / 2, 64),
>>  				       GL_TRUE);
>>        if (!irb->region)
>>  	return false;
> 
> This looks like it would fail on a buffer with height = 129.  Doesn't
> seem like 128 pitch requirement would be needed -- has it been tested?
> 
>> diff --git a/src/mesa/drivers/dri/intel/intel_span.c b/src/mesa/drivers/dri/intel/intel_span.c
>> index 153803f..d306432 100644
>> --- a/src/mesa/drivers/dri/intel/intel_span.c
>> +++ b/src/mesa/drivers/dri/intel/intel_span.c
>> @@ -131,38 +131,77 @@ intel_set_span_functions(struct intel_context *intel,
>>     int miny = 0;							\
>>     int maxx = rb->Width;						\
>>     int maxy = rb->Height;						\
>> -   int stride = rb->RowStride;						\
>> -   uint8_t *buf = rb->Data;						\
>> +									\
>> +   /*									\
>> +    * Here we ignore rb->Data and rb->RowStride as set by		\
>> +    * intelSpanRenderStart. Since intel_offset_S8 decodes the W tile	\
>> +    * manually, the region's *real* base address and stride is		\
>> +    * required.								\
>> +    */									\
>> +   struct intel_renderbuffer *irb = intel_renderbuffer(rb);		\
>> +   uint8_t *buf = irb->region->buffer->virtual;				\
>> +   unsigned stride = irb->region->pitch;				\
>> +   unsigned height = 2 * irb->region->height;				\
>> +   bool flip = rb->Name == 0;						\
>>  
>> -/* Don't flip y. */
>>  #undef Y_FLIP
>> -#define Y_FLIP(y) y
>> +#define Y_FLIP(y) ((1 - flip) * y + flip * (height - 1 - y))
> 
> The flip is usually handled by a scale and bias variable, so that Y_FLIP
> is ((y) * scale + bias).  I think it'll produce less code, since Y_FLIP
> is used a lot.

Good call. Does changing the hunk like this look good to you?

+   struct intel_renderbuffer *irb = intel_renderbuffer(rb);		\
+   uint8_t *buf = irb->region->buffer->virtual;			\
+   unsigned stride = irb->region->pitch;				\
+   unsigned height = 2 * irb->region->height;				\
+   bool flip = rb->Name == 0;						\
+   int y_scale = flip ? -1 : 1;					\
+   int y_bias = flip ? (height - 1) : 0;				\

-/* Don't flip y. */
 #undef Y_FLIP
-#define Y_FLIP(y) y
+#define Y_FLIP(y) (y_scale * (y) + y_bias)


-- 
Chad Versace
chad@chad-versace.us


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