Re: [PATCH v2 1/7] drm/i915/gen8: Add infrastructure to initialize WA batch buffers

["Siluvery, Arun" <arun.siluvery@linux.intel.com>]

On 29/05/2015 19:16, Chris Wilson wrote:
> On Fri, May 29, 2015 at 07:03:19PM +0100, Arun Siluvery wrote:
>> This patch adds functions to setup WA batch buffers but they are not yet
>> enabled in this patch. Some of the WA are to be applied during context save
>> but before restore and some at the end of context save/restore but before
>> executing the instructions in the ring, WA batch buffers are created for
>> this purpose and these WA cannot be applied using normal means.
>>
>> Signed-off-by: Namrta <namrta.salonie@intel.com>
>> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_drv.h  |   3 ++
>>   drivers/gpu/drm/i915/intel_lrc.c | 101 +++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 104 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index 731b5ce..dd4b31d 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -814,6 +814,9 @@ struct intel_context {
>>
>>   	/* Execlists */
>>   	bool rcs_initialized;
>> +	struct intel_ringbuffer *indirect_ctx_wa_bb;
>> +	struct intel_ringbuffer *per_ctx_wa_bb;
>
> Eh? They are only command sequences whose starting addresses you encode
> into the execlists context. Why have you allocated a ringbuf not an
> object? Why have you allocated 2 pages when you only need one, and could
> even find space elsewhere in the context....

ringbuf is only used so that I can use logical_ring_*(), object can also 
be used.
Single page is enough but since we have two batch buffers and need to 
provide offsets in two different registers, two pages are used for 
simplifying things, I guess we can manage with single page, I will try this.

Your idea of using space in context itself simplifies many things but 
the context size varies across Gens, is it safe to pick last page or 
increase the size by one more page and use that to load these 
instructions? I think using an additional page is safe to avoid the risk 
of HW overwriting that page or do you have any other recommendation? I 
will first try and see if it works.

>
> And these should be pinned alongside the context *not permanently*.
right, I will correct this but this won't be required if we use the 
space in context.

>
> I want a debug mode that limits us to say 16M of GGTT space so that
> these address space leaks are easier to demonstrate in practice.
> -Chris
>

regards
Arun

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