[Mesa-dev] [PATCH 08/10] i965: Introduce an OUT_RELOC64 macro.

[Kenneth Graunke]

On 12/13/2013 09:28 AM, Daniel Vetter wrote:
> On Thu, Dec 12, 2013 at 01:26:40AM -0800, Kenneth Graunke wrote:
>> Broadwell uses 48-bit addresses.  The first DWord is the low 32 bits,
>> and the second DWord is the high 16 bits.
>>
>> Since individual buffers shouldn't be larger than 4GB in size, any
>> offsets into those buffers (buffer->offset + delta) should fit in the
>> low 32 bits.  So I believe we can simply emit 0 for the high 16-bits,
>> and drm_intel_bo_emit_reloc() should patch it up.
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> ---
>>  src/mesa/drivers/dri/i965/intel_batchbuffer.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.h b/src/mesa/drivers/dri/i965/intel_batchbuffer.h
>> index 159f928..128eed9 100644
>> --- a/src/mesa/drivers/dri/i965/intel_batchbuffer.h
>> +++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.h
>> @@ -178,6 +178,11 @@ void intel_batchbuffer_cached_advance(struct brw_context *brw);
>>  				read_domains, write_domain, delta);	\
>>  } while (0)
>>  
>> +/* Handle 48-bit address relocations for Gen8+ */
>> +#define OUT_RELOC64(buf, read_domains, write_domain, delta) \
>> +   OUT_RELOC(buf, read_domains, write_domain, delta);       \
>> +   OUT_BATCH(0);
> 
> Please not. The presumed_offset that libdrm uses is 64bits, and you need
> to emit the full presumed address (and correctly shifted). Atm the kernel
> never gives you a presumed reloc offset with the high bits set so it
> doesn't matter. But I'd prefer if we don't need to make this opt-in
> behaviour once we enable address spaces with more than 4G.
> 
> i-g-t gets away with the cheap hack since we're allowed to break igt.
> Let me check ddx and libva whether I've lost this fight already ...
> -Daniel

I'm more than happy to do the right thing, I just don't know what that
is.  I don't see any uint64_t values in the interface we use at all:

OUT_RELOC becomes
   ret = drm_intel_bo_emit_reloc(brw->batch.bo, 4*brw->batch.used,
                                 buffer, delta,
                                 read_domains, write_domain);

which is:

static int
drm_intel_gem_bo_emit_reloc(drm_intel_bo *bo, uint32_t offset,
                drm_intel_bo *target_bo, uint32_t target_offset,
                uint32_t read_domains, uint32_t write_domain)

...all 32-bit values.  It sounds like you're thinking we use Chris's
"let's presume it hasn't moved since last time" relocation stuff?  We
don't (at least not yet)...

I'm more than happy to take suggestions.

--Ken