From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71CB4C4332F for ; Wed, 1 Jun 2022 12:36:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352956AbiFAMgA (ORCPT ); Wed, 1 Jun 2022 08:36:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58928 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352989AbiFAMfl (ORCPT ); Wed, 1 Jun 2022 08:35:41 -0400 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72A92A0D00 for ; Wed, 1 Jun 2022 05:35:40 -0700 (PDT) Received: by mail-wr1-x42a.google.com with SMTP id s24so2145052wrb.10 for ; Wed, 01 Jun 2022 05:35:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=geWAW2xPBu0qLpWdiPyBgNivVlwU5h/jMqQrbUnnVfs=; b=BdiXXMzt8D06LixSdY84NDu9Ost8vce1JU5Ly7m8KGGcWhLpUhElYtn+kEPfDuaH/W ND88PNMAtKQj+HfoxEaDWhcrBetkIBFbdqglb7wVKPfHO9j+2zS1NmYUaejOw1aou2eM 2E2nTMfjIdKfDATqam2LNbA4ivHfMMsaofjKI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=geWAW2xPBu0qLpWdiPyBgNivVlwU5h/jMqQrbUnnVfs=; b=xx5N2tu7HfczS59W+DmnxRILYE+Aen3kwUhb9BHWb951rlAyLDBxHeUmx+Q2hFyEom kWMPkyrZ3Ca4Kv7YSv500Qr0s2b1Z22eU/m9n6VLZvnDigh3qbKrC9dIdVJbDguQTcar 6ylXtbCfbVjij8qir2xCPraYw6ddefHdIRVBedP8EuuTW3/KHvCqWEYVIKBMrlcqG7AI fr/9Jkzk55LbZ9InJKDyekEdjv19I8nje5zejLEQEAqhjVRNLkWewYQad0Fm/7kuZTMu Dk1orPO69xjaK1fO1JXGrYIs1tUVdrIDArQTEfvCzRVTxcoI7xY95rJgrw4E8e+NZ6Sb IJtQ== X-Gm-Message-State: AOAM530qzmbXeDgRUF18Q22Mb9euC829DcpsmXFhM75j2qCMkTvIGMKE N9yPIJ6s+Bzf3/ZA3/JD5bwtyQ== X-Google-Smtp-Source: ABdhPJzRlsH0LJwGkcjJA/JqoeBghm0kDNaIwYUbkjauNpnH8gIwKHdrawPBSHH7gN216H+LRzl0Uw== X-Received: by 2002:a5d:43cd:0:b0:20c:fdbd:8c11 with SMTP id v13-20020a5d43cd000000b0020cfdbd8c11mr53732471wrr.7.1654086938960; Wed, 01 Jun 2022 05:35:38 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id d12-20020a5d4f8c000000b00210346cd0b7sm1537054wru.101.2022.06.01.05.35.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jun 2022 05:35:38 -0700 (PDT) Date: Wed, 1 Jun 2022 14:35:35 +0200 From: Daniel Vetter To: Maxime Ripard Cc: Samuel Holland , Heiko =?iso-8859-1?Q?St=FCbner?= , Sandy Huang , dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, Alistair Francis , =?utf-8?Q?Ond=C5=99ej?= Jirman , Andreas Kemnade , David Airlie , Geert Uytterhoeven , Krzysztof Kozlowski , Liang Chen , Maarten Lankhorst , Michael Riesch , Nicolas Frattaroli , Peter Geis , Rob Herring , Sam Ravnborg , Thierry Reding , Thomas Zimmermann , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 00/16] drm/rockchip: Rockchip EBC ("E-Book Controller") display driver Message-ID: Mail-Followup-To: Maxime Ripard , Samuel Holland , Heiko =?iso-8859-1?Q?St=FCbner?= , Sandy Huang , dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, Alistair Francis , =?utf-8?Q?Ond=C5=99ej?= Jirman , Andreas Kemnade , David Airlie , Geert Uytterhoeven , Krzysztof Kozlowski , Liang Chen , Maarten Lankhorst , Michael Riesch , Nicolas Frattaroli , Peter Geis , Rob Herring , Sam Ravnborg , Thierry Reding , Thomas Zimmermann , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20220413221916.50995-1-samuel@sholland.org> <20220414085018.ayjvscgdkoen5nw5@houat> <20220531085835.grw5nt4vyofis3po@penduick> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220531085835.grw5nt4vyofis3po@penduick> X-Operating-System: Linux phenom 5.10.0-8-amd64 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Tue, May 31, 2022 at 10:58:35AM +0200, Maxime Ripard wrote: > Hi Daniel, > > Thanks for your feedback > > On Wed, May 25, 2022 at 07:18:07PM +0200, Daniel Vetter wrote: > > > > VBLANK Events and Asynchronous Commits > > > > ====================================== > > > > When should the VBLANK event complete? When the pixels have been blitted > > > > to the kernel's shadow buffer? When the first frame of the waveform is > > > > sent to the panel? When the last frame is sent to the panel? > > > > > > > > Currently, the driver is taking the first option, letting > > > > drm_atomic_helper_fake_vblank() send the VBLANK event without waiting on > > > > the refresh thread. This is the only way I was able to get good > > > > performance with existing userspace. > > > > > > I've been having the same kind of discussions in private lately, so I'm > > > interested by the answer as well :) > > > > > > It would be worth looking into the SPI/I2C panels for this, since it's > > > basically the same case. > > > > So it's maybe a bit misnamed and maybe kerneldocs aren't super clear (pls > > help improve them), but there's two modes: > > > > - drivers which have vblank, which might be somewhat variable (VRR) or > > become simulated (self-refresh panels), but otherwise is a more-or-less > > regular clock. For this case the atomic commit event must match the > > vblank events exactly (frame count and timestamp) > > Part of my interrogation there is do we have any kind of expectation > on whether or not, when we commit, the next vblank is going to be the > one matching that commit or we're allowed to defer it by an arbitrary > number of frames (provided that the frame count and timestamps are > correct) ? In general yes, but there's no guarantee. The only guarante we give for drivers with vblank counters is that if you receive a vblank event (flip complete or vblank event) for frame #n, then an immediate flip/atomic ioctl call will display earliest for frame #n+1. Also usually you should be able to hit #n+1, but even today with fun stuff like self refresh panels getting out of self refresh mode might take a bit more than a few frames, and so you might end up being late. But otoh if you just do a page flip loop then on average (after the crtc is fully resumed) you should be able to update at vrefresh rate exactly. > > - drivers which don't have vblank at all, mostly these are i2c/spi panels > > or virtual hw and stuff like that. In this case the event simply happens > > when the driver is done with refresh/upload, and the frame count should > > be zero (since it's meaningless). > > > > Unfortuantely the helper to dtrt has fake_vblank in it's name, maybe > > should be renamed to no_vblank or so (the various flags that control it > > are a bit better named). > > > > Again the docs should explain it all, but maybe we should clarify them or > > perhaps rename that helper to be more meaningful. > > > > > > Blitting/Blending in Software > > > > ============================= > > > > There are multiple layers to this topic (pun slightly intended): > > > > 1) Today's userspace does not expect a grayscale framebuffer. > > > > Currently, the driver advertises XRGB8888 and converts to Y4 > > > > in software. This seems to match other drivers (e.g. repaper). > > > > > > > > 2) Ignoring what userspace "wants", the closest existing format is > > > > DRM_FORMAT_R8. Geert sent a series[4] adding DRM_FORMAT_R1 through > > > > DRM_FORMAT_R4 (patch 9), which I believe are the "correct" formats > > > > to use. > > > > > > > > 3) The RK356x SoCs have an "RGA" hardware block that can do the > > > > RGB-to-grayscale conversion, and also RGB-to-dithered-monochrome > > > > which is needed for animation/video. Currently this is exposed with > > > > a V4L2 platform driver. Can this be inserted into the pipeline in a > > > > way that is transparent to userspace? Or must some userspace library > > > > be responsible for setting up the RGA => EBC pipeline? > > > > > > I'm very interested in this answer as well :) > > > > > > I think the current consensus is that it's up to userspace to set this > > > up though. > > > > Yeah I think v4l mem2mem device is the answer for these, and then > > userspace gets to set it all up. > > I think the question wasn't really about where that driver should be, > but more about who gets to set it up, and if the kernel could have > some component to expose the formats supported by the converter, but > whenever a commit is being done pipe that to the v4l2 device before > doing a page flip. > > We have a similar use-case for the RaspberryPi where the hardware > codec will produce a framebuffer format that isn't standard. That > format is understood by the display pipeline, and it can do > writeback. > > However, some people are using a separate display (like a SPI display > supported by tinydrm) and we would still like to be able to output the > decoded frames there. > > Is there some way we could plumb things to "route" that buffer through > the writeback engine to perform a format conversion before sending it > over to the SPI display automatically? Currently not transparently. Or at least no one has done that, and I'm not sure that's really a great idea. With big gpus all that stuff is done with separate command submission to the render side of things, and you can fully pipeline all that with in/out-fences. Doing that in the kms driver side in the kernel feels very wrong to me :-/ -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch