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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DDECC43381 for ; Fri, 29 Mar 2019 15:07:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A86E2075E for ; Fri, 29 Mar 2019 15:07:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729468AbfC2PHf (ORCPT ); Fri, 29 Mar 2019 11:07:35 -0400 Received: from relay10.mail.gandi.net ([217.70.178.230]:50915 "EHLO relay10.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728720AbfC2PHf (ORCPT ); Fri, 29 Mar 2019 11:07:35 -0400 Received: from aptenodytes (aaubervilliers-681-1-91-136.w90-88.abo.wanadoo.fr [90.88.32.136]) (Authenticated sender: paul.kocialkowski@bootlin.com) by relay10.mail.gandi.net (Postfix) with ESMTPSA id 15266240006; Fri, 29 Mar 2019 15:07:29 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers From: Paul Kocialkowski To: Daniel Vetter Cc: Eric Anholt , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , Eben Upton , Thomas Petazzoni Date: Fri, 29 Mar 2019 16:07:29 +0100 In-Reply-To: <20190328185307.GZ2665@phenom.ffwll.local> References: <20190320154809.14823-1-paul.kocialkowski@bootlin.com> <20190320154809.14823-2-paul.kocialkowski@bootlin.com> <87zhpph4c2.fsf@anholt.net> <82618ee8c2a2380a62b1fb894e5c35c602e20f3d.camel@bootlin.com> <20190328185307.GZ2665@phenom.ffwll.local> Organization: Bootlin Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Le jeudi 28 mars 2019 à 19:53 +0100, Daniel Vetter a écrit : > On Thu, Mar 21, 2019 at 04:27:06PM +0100, Paul Kocialkowski wrote: > > Hi, > > > > Le mercredi 20 mars 2019 à 09:56 -0700, Eric Anholt a écrit : > > > Paul Kocialkowski writes: > > > > > > > The firstopen DRM driver hook was initially used to perform hardware > > > > initialization, which is now considered legacy. Only a single user of > > > > firstopen remains at this point (savage). > > > > > > > > In some specific cases, non-legacy drivers may also need to implement > > > > these hooks. For instance on VC4, we need to allocate a 16 MiB buffer > > > > for the GPU. Because it's not required for fbcon, it's a waste to > > > > allocate it before userspace starts using the DRM device. > > > > > > > > Using firstopen and lastclose for this allocation seems like the best > > > > fit, so re-habilitate the hook to allow it to be called for non-legacy > > > > drivers. > > > > > > > > Signed-off-by: Paul Kocialkowski > > > > --- > > > > drivers/gpu/drm/drm_file.c | 3 +-- > > > > include/drm/drm_drv.h | 2 +- > > > > 2 files changed, 2 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > > > > index b1838a41ad43..c011b5cbfb6b 100644 > > > > --- a/drivers/gpu/drm/drm_file.c > > > > +++ b/drivers/gpu/drm/drm_file.c > > > > @@ -266,8 +266,7 @@ static int drm_setup(struct drm_device * dev) > > > > { > > > > int ret; > > > > > > > > - if (dev->driver->firstopen && > > > > - drm_core_check_feature(dev, DRIVER_LEGACY)) { > > > > + if (dev->driver->firstopen) { > > > > ret = dev->driver->firstopen(dev); > > > > if (ret != 0) > > > > return ret; > > > > diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h > > > > index ca46a45a9cce..aa14607e54d4 100644 > > > > --- a/include/drm/drm_drv.h > > > > +++ b/include/drm/drm_drv.h > > > > @@ -236,7 +236,7 @@ struct drm_driver { > > > > * to set/unset the VT into raw mode. > > > > * > > > > * Legacy drivers initialize the hardware in the @firstopen callback, > > > > - * which isn't even called for modern drivers. > > > > + * modern drivers can use it for other purposes only. > > > > */ > > > > void (*lastclose) (struct drm_device *); > > > > > > Our usage in vc4 is not very different from what we called "hardware > > > initialization" in other devices. I would rather just delete this > > > sentence entirely. > > > > Sounds good to me! > > > > > The only alternative I can think of to using a firstopen/lastclose-style > > > allocation for this would be to allocate the bin bo on the first > > > (non-dumb?) V3D BO allocation and refcount those to free the binner. > > > > I don't see other options either, and using firstclose/lastopen feels > > overall more readable in the driver code. > > > > I'm not sure there is such a big overhead associated with allocating > > the binner BO (it seems that the current implementation tries to alloc > > until the specific memory constraints for the buffer are met, so > > perhaps that can take time). But if there is, I suppose it's best to > > have that when starting up rather than delaying the first render > > operation. > > I'm not entirely buying the "we don't need this for fbcon only" argument - > there's plenty of dumb kms clients too (boot splash and whatever else > there might be). If you don't want to keep this around I think allocating > on first non-dumb bo allocation and dropping it when the last such fd > closes sounds like a much better idea. Needs a bit more state, you need to > track per drm_file whether you've already allocated a non-dumb bo, and a > drm_device refcount, but that's not much. Firstopen feels like the wrong > thing. This is quite a valid point, but we decided to go for a middle-ground between always allocating and allocating at the first GPU op, so that the operation is not significantly delayed by allocating the buffer. > Another option would be first_renderopen or something like that, except > you can also render on the legacy node and I'm not sure how much there's a > demand for this in other drivers. In the end you have open/close > callbacks, you can do all the driver specific things you want to do in > there. Yes I've initially tried playing with that and reached the same conclusion: there can be render ops on the legacy node too so this is just not reliable for what we're trying to do. > Aside: I kinda also want to ditch lastclose usage. There's fbdev (we have a > better solution with Noralf's drm_client for those) and runtime pm (which > frankly is just a cheap hack, I want my gpu to susepend also when it's not > in use when all the screens are off, not only when I killed X and > everything). I understand that, yes. I don't see any issue with a implementation tracking the state in open if we really want firstopen/lastclose to disappear. Cheers, Paul -- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com