[Intel-gfx] [PATCH v2] drm/i915/vlv: Update Wait for FIFO and wait for 20 free entries. v2

[Daniel Vetter]

[re-adding intel-gfx]

On Tue, Dec 3, 2013 at 5:05 PM, S, Deepak <deepak.s at intel.com> wrote:
> Hi Daniel/Chris,
>
> I spent some time in digging through the specs and also has chatted with couple of people. Below is my understanding of the FIFO.
>
> "On SB, Out of 64 FIFO Entries, 20 Entries will be used by HW and remaining 44 will be used by the SW,. I think due to this reason, we have a threshold of 20 Entries."
>
> "On VLV, HW and SW can access all 64 fifo entries, I don't think having a threshold of 20 Entries is mandatory on VLV. Also, since both SW and HW can access all 64 Entries. I think on VLV, we need to update the fifo_count before waiting for the FIFO."
>
> Please correct me if I am working.

Looks sane. I've added this to the commit message and merged your patch.

Thanks,

Daniel

>
> Thanks
> Deepak
>
> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel Vetter
> Sent: Friday, November 29, 2013 7:33 PM
> To: S, Deepak
> Cc: Chris Wilson; intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH v2] drm/i915/vlv: Update Wait for FIFO and wait for 20 free entries. v2
>
> On Fri, Nov 29, 2013 at 11:53:44AM +0000, S, Deepak wrote:
>> Sure Chris, I will recheck the spec and change the commit accordingly.
>
> I guess the big question is why vlv is special. We've had these 20 fifo entries ever since gen6, so I'd also really like to know what suddenly changed. Even the 20 entries have just been copied from a spec with no explation. So if this is to allow hw writes to the gt from the display, then I guess we would need this change on all gen6+ platforms?
>
> Hence digging through specs or dragging a hw engineer into this discussion would be highly appreciated.
>
> Thanks, Daniel
>
>>
>> -----Original Message-----
>> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
>> Sent: Friday, November 29, 2013 5:07 PM
>> To: S, Deepak
>> Cc: intel-gfx at lists.freedesktop.org
>> Subject: Re: [Intel-gfx] [PATCH v2] drm/i915/vlv: Update Wait for FIFO
>> and wait for 20 free entries. v2
>>
>> On Fri, Nov 29, 2013 at 11:22:32AM +0000, S, Deepak wrote:
>> > Hi Chris,
>> >
>> > In VLV, both hardware and software can use the write fifo in parallel, we are adding this change as a water mark to make sure we atleast have 20 free entries .This will help us to avoid software mmio write being dropped.
>>
>> Please think some more and describe the change exactly.
>> -Chris
>>
>> --
>> Chris Wilson, Intel Open Source Technology Centre
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch