[Intel-gfx] [PATCH 21/39] drm/i915/guc: Disable global reset

[Daniele Ceraolo Spurio]

On 01/07/2019 01:35 PM, Chris Wilson wrote:
> Quoting Daniele Ceraolo Spurio (2019-01-07 21:28:48)
>>
>> On 01/07/2019 10:50 AM, Chris Wilson wrote:
>>> Quoting Daniele Ceraolo Spurio (2019-01-07 18:31:52)
>>>>
>>>> Were you already
>>>> planning/working on something along the lines of the possible solution
>>>> mentioned in the commit message? Just trying to understand what the
>>>> status is before jumping in to avoid duplication of work ;)
>>>
>>> The compromises required (reserving space for the firmware) seem like it
>>> will just end up with a lot of screaming to make it mutexless today.
>>
>> Aren't we already keeping some GuC stuff perma-pinned (e.g. the
>> stage_desc_pool)? Current Gen11+ firmware needs more space and uses
>> objects up to tens of MBs, the blobs aren't that big in comparison.
> 
> Hmm, there's always the guc reserved region (top/bottom). Is that large
> enough to store the firmware, and would it be legal to load from those
> addresses? (After the dma transfer we wouldn't use those ourselves, so
> the guc is free to utilise them for its scratch. Then after the guc is
> reset, we would put the firmware there again for dma xfer).
> -Chris
> 

I've asked and the DMA engine should be able to fetch from there, so 
this sounds like quite a good compromise. We wouldn't need to move the 
blob after the reset either because those regions are not accessible at 
all by GuC and they're not used by the firmware in any way. The top 
region in particular is several MBs big, so the firmware would fit quite 
nicely in there.

Daniele