On 01/05/2016 03:44 PM, Daniel Vetter wrote:
On Mon, Jan 04, 2016 at 07:18:26PM +0530, Kumar, Shobhit wrote:
On 12/23/2015 08:22 AM, Kumar, Shobhit wrote:
On 12/21/2015 05:39 PM, Daniel Vetter wrote:
On Fri, Dec 18, 2015 at 07:24:19AM -0800, Matt Roper wrote:
On Fri, Dec 18, 2015 at 07:14:17AM -0800, Matt Roper wrote:
On Fri, Dec 18, 2015 at 05:10:12PM +0200, Ville Syrjälä wrote:
On Fri, Dec 18, 2015 at 06:58:58AM -0800, Matt Roper wrote:
On Fri, Dec 18, 2015 at 12:35:47PM +0200, Ville Syrjälä wrote:
On Wed, Dec 16, 2015 at 07:06:20PM -0800, Radhakrishna Sripada
wrote:
Original value of 32 blocks is not sufficient when using cursor
size of
256x256 causing FIFO underruns when the reworked wm
caluclations in
commit 024c9045221fe45482863c47c4b4c47d37f97cbf
Author: Matt Roper <matthew.d.roper@xxxxxxxxx>
Date: Thu Sep 24 15:53:11 2015 -0700
drm/i915/skl: Eliminate usage of pipe_wm_parameters from
SKL-style WM (v4)
Well that commit is obviously incorrect. It's now using the pipe src
width as the plane width for all planes.
Yeah, we already noted that bug in another email thread, but decided
that it was unrelated to the problems Radhakrishna is facing.
Radhakrishna is only using a cursor (which doesn't use that buggy
function)
Pop quiz: what does it use then?
All non-cursor planes (i.e., primary+sprite). Cursors use a fixed DDB
allocation (currently 32 blocks as suggested by bspec, but
Radhakrishna's testing has found this to be too small, so his patch
here
is bumping that number up.
To elaborate on this some more, we have some suspicions about why the
bspec-suggested 32 blocks might not be enough. There's some new
workaround information in the bspec about sometimes needing to disable
the system agent (SAGV) on non-BXT gen9, depending on the configuration
and that's not something that's been implemented in our driver code yet.
There's also another new workaround that checks raw system memory
bandwidth and adjusts watermark programming that hasn't been implemented
yet either. It could be that one of those two missing workarounds is
the true culprit, but Radhakrishna's patch here looks like a reasonable
short-term workaround; my main worry is that if he needs to bump the
hardcoded 32 up to to 52 for the single pipe case, he might also need to
bump the hardcoded 8 up as well for the multi-pipe case; I don't think
anyone has tested that yet (and this seems to be a SKL-specific problem,
so I can't reproduce it on my BXT).
This needs at least a very big comment that we're just hacking around
with
duct-tape. Also allocating DDB shouldn't matter for correctness, as long
as we compute the WM values correctly. I wonder how this fixes anything
really (except making it a bit harder to hit perhaps due to the enlarged
buffering it affords for the cursor).
Agree Daniel, but in our detailed testing this is found to have fixed
reliably all known flickers. I recommend to have a detailed comment and
*put* the duct-tape. I can have a rerun of detailed tests again to
ensure that its indeed fixing everything.
Imo better to just implement the other workarounds first, then see what's
left.
I know there are few known workarounds pending. Lets continue
implementing them and more. But with Matt's patch not fixing the issue,
lets take this as an immediate short term fix and come back to remove
the duct-tape when we have correct fix.
I experimented and found that reverting this patch but having arbitrated
display bandwidth based workaround to increase latency values for all levels
is fixing the flicker. Will be working on this along with Mahesh, unless
Matt, you have a patch for this already.
Excellent, really happy that we can go ahead with a reasonable looking fix
right away here.
Daniel, we implemented the memory latency increase for quick test and it
worked, but in reality that situation was not hitting even with a QHD
eDP and 4k@60 DP with a two channel 1867 MHz memory. So this was not a
solution.
There have been another patch series to try to fix this that I posted -
https://patchwork.freedesktop.org/patch/71758/
and we have been trying with lot of Matt's patches for watermark, and
along with what I posted but all of this has not yielded perfect under
run error free results though improved a little.
But cursor DDB bump for both internal and external pipe is resulting in
complete fix of the problem. As of now that is the only solution I can
think off and has been extensively tested with QHD eDP/ 19x10 eDP + 4k
DP/HDMI and working reliably. I think we should be dynamically
allocating cursor DDB as well so that it will increase the DDB if cursor
size is big.
But for now proposal is to statically increase these cursor DDB to 52
for single pipe as in this patch and additionally have it 32 in case of
multi pipe scenario. Once we have all water mark thingy sorted out, we
can come back and re-look at this.
Regards
Shobhit
Thanks, Daniel
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