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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 1F2D3C433FE for ; Tue, 14 Sep 2021 14:36:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0AC4A60698 for ; Tue, 14 Sep 2021 14:36:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234523AbhINOht (ORCPT ); Tue, 14 Sep 2021 10:37:49 -0400 Received: from wnew2-smtp.messagingengine.com ([64.147.123.27]:39265 "EHLO wnew2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234538AbhINOhM (ORCPT ); Tue, 14 Sep 2021 10:37:12 -0400 Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailnew.west.internal (Postfix) with ESMTP id 540172B01324; Tue, 14 Sep 2021 10:35:48 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute1.internal (MEProxy); Tue, 14 Sep 2021 10:35:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cerno.tech; h= date:from:to:cc:subject:message-id:references:mime-version :content-type:in-reply-to; s=fm3; bh=gzQp1QWFJ1terVGLXG3LkelZHX1 PY0zeCf7c+zfmKMQ=; b=qwrojLetWm8vSiNaOYOzvA/4bx5c9Ldp0mN1akY5Tic XOFC+LZ3NHVFZI0Q4j2gV0uL7YEnEhe21l1M5TJFRig2DKZ4Un6hDXjgQOii1Y82 5WyO4KZZoNqJ7oKdX2MwmOfMWRot1Q9AgXdATsPsVVG1riN9nlnyyYDqXn3YFXN+ 9s2V28gn97sb698EtmBEz1ccHFSZHOl3o33DXtlw99spoJ9ov5lx4oe2vyal1Z25 oC6aWg/N2xi93fEny5sIuxmWO0VPSLBWD1xzy12AF01w9pCYn7bWBQxuyyMCpvaM y39vOL7n4ExOP5RKVrgIgcSbtNTWg/52A2XQpR9ZJ2g== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm3; bh=gzQp1Q WFJ1terVGLXG3LkelZHX1PY0zeCf7c+zfmKMQ=; b=c/mMgHLb69f6Km6Eo4UNJk iqu9ZZm7TixCWDggjEknfbBqsJ52MzYz/I4E70KNWN/WqGb3DQztg8k8Yrg3GJWH j2J6KLBaFTzsJxJV91N4IKyxV0/a6O4XJ3IvpCkAC8pP6I0sr3cNzGcMlPlA8env X2ImR9ouayJUHXEp/1vY0qlG+uEifOqaQSSqfF8UuJkExlp3xMnD0e7qfgfD0Sg1 OE5DWmY8f3GCZHWtF+3JmCP1ZfpRdijxPE1U4kDXV43gPOKkuJp+IpDKyKvq8XYx 80xU/GYYirii0rkNFO/4xy2V+mCPAhIrhQzaztYQ68dD9DiEY6KnX9Q9zY8okcEw == X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvtddrudegledgjeejucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvffukfhfgggtuggjsehgtderredttddunecuhfhrohhmpeforgigihhm vgcutfhiphgrrhguuceomhgrgihimhgvsegtvghrnhhordhtvggthheqnecuggftrfgrth htvghrnhepuddvudfhkeekhefgffetffelgffftdehffduffegveetffehueeivddvjedv gfevnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepmh grgihimhgvsegtvghrnhhordhtvggthh X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 14 Sep 2021 10:35:44 -0400 (EDT) Date: Tue, 14 Sep 2021 16:35:41 +0200 From: Maxime Ripard To: Andrzej Hajda Cc: Sam Ravnborg , Daniel Vetter , David Airlie , Jonas Karlman , Laurent Pinchart , Thierry Reding , Maarten Lankhorst , Thomas Zimmermann , Neil Armstrong , Robert Foss , Jernej Skrabec , Sean Paul , freedreno@lists.freedesktop.org, Kyungmin Park , linux-kernel@vger.kernel.org, Xinliang Liu , Seung-Woo Kim , Tian Tao , Inki Dae , linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org, Rob Clark , dri-devel@lists.freedesktop.org, John Stultz , Chen Feng , Xinwei Kong , Joonyoung Shim Subject: Re: [PATCH v4 02/24] drm/bridge: Document the probe issue with MIPI-DSI bridges Message-ID: <20210914143541.433ucx2kvz36tw42@gilmour> References: <20210910101218.1632297-1-maxime@cerno.tech> <20210910101218.1632297-3-maxime@cerno.tech> <7ad18d53-3ad6-a614-a8e1-cce6505f90a8@samsung.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="6br4ofwy642o3hq4" Content-Disposition: inline In-Reply-To: <7ad18d53-3ad6-a614-a8e1-cce6505f90a8@samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org --6br4ofwy642o3hq4 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Mon, Sep 13, 2021 at 08:29:37AM +0200, Andrzej Hajda wrote: >=20 > W dniu 10.09.2021 o=A012:11, Maxime Ripard pisze: > > Interactions between bridges, panels, MIPI-DSI host and the component > > framework are not trivial and can lead to probing issues when > > implementing a display driver. Let's document the various cases we need > > too consider, and the solution to support all the cases. > > > > Signed-off-by: Maxime Ripard > > --- > > Documentation/gpu/drm-kms-helpers.rst | 6 +++ > > drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ > > 2 files changed, 63 insertions(+) > > > > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/= drm-kms-helpers.rst > > index 10f8df7aecc0..ec2f65b31930 100644 > > --- a/Documentation/gpu/drm-kms-helpers.rst > > +++ b/Documentation/gpu/drm-kms-helpers.rst > > @@ -157,6 +157,12 @@ Display Driver Integration > > .. kernel-doc:: drivers/gpu/drm/drm_bridge.c > > :doc: display driver integration > > =20 > > +Special Care with MIPI-DSI bridges > > +---------------------------------- > > + > > +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c > > + :doc: special care dsi > > + > > Bridge Operations > > ----------------- > > =20 > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > > index baff74ea4a33..7cc2d2f94ae3 100644 > > --- a/drivers/gpu/drm/drm_bridge.c > > +++ b/drivers/gpu/drm/drm_bridge.c > > @@ -96,6 +96,63 @@ > > * documentation of bridge operations for more details). > > */ > > =20 > > +/** > > + * DOC: special care dsi > > + * > > + * The interaction between the bridges and other frameworks involved in > > + * the probing of the upstream driver and the bridge driver can be > > + * challenging. Indeed, there's multiple cases that needs to be > > + * considered: > > + * > > + * - The upstream driver doesn't use the component framework and isn't= a > > + * MIPI-DSI host. In this case, the bridge driver will probe at some > > + * point and the upstream driver should try to probe again by return= ing > > + * EPROBE_DEFER as long as the bridge driver hasn't probed. > > + * > > + * - The upstream driver doesn't use the component framework, but is a > > + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be > > + * controlled. In this case, the bridge device is a child of the > > + * display device and when it will probe it's assured that the displ= ay > > + * device (and MIPI-DSI host) is present. The upstream driver will be > > + * assured that the bridge driver is connected between the > > + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operation= s. > > + * Therefore, it must run mipi_dsi_host_register() in its probe > > + * function, and then run drm_bridge_attach() in its > > + * &mipi_dsi_host_ops.attach hook. > > + * > > + * - The upstream driver uses the component framework and is a MIPI-DSI > > + * host. The bridge device uses the MIPI-DCS commands to be > > + * controlled. This is the same situation than above, and can run > > + * mipi_dsi_host_register() in either its probe or bind hooks. > > + * > > + * - The upstream driver uses the component framework and is a MIPI-DSI > > + * host. The bridge device uses a separate bus (such as I2C) to be > > + * controlled. In this case, there's no correlation between the probe > > + * of the bridge and upstream drivers, so care must be taken to avoid > > + * an endless EPROBE_DEFER loop, with each driver waiting for the > > + * other to probe. > > + * > > + * The ideal pattern to cover the last item (and all the others in the > > + * MIPI-DSI host driver case) is to split the operations like this: > > + * > > + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its > > + * probe hook. It will make sure that the MIPI-DSI host sticks aroun= d, > > + * and that the driver's bind can be called. > > + * > > + * - In its probe hook, the bridge driver must try to find its MIPI-DSI > > + * host, register as a MIPI-DSI device and attach the MIPI-DSI device > > + * to its host. The bridge driver is now functional. > > + * > > + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host c= an > > + * now add its component. Its bind hook will now be called and since > > + * the bridge driver is attached and registered, we can now look for > > + * and attach it. > > + * > > + * At this point, we're now certain that both the upstream driver and > > + * the bridge driver are functional and we can't have a deadlock-like > > + * situation when probing. > > + */ > > + > > static DEFINE_MUTEX(bridge_lock); > > static LIST_HEAD(bridge_list); >=20 >=20 > Nice work with documenting this initialization dance. It clearly shows=20 > that bridge API lacks better mechanism - usage of mipi dsi callbacks to= =20 > get notifications about bridge appearance is ugly. Yeah, there's so many moving parts it's definitely not great. > It remains me my resource tracking patches which I have posted long > time ago [1] - they would solve the issue in much more elegant way, > described here [2]. Apparently I was not stubborn enough in promoting > this solution. Wow, that sounds like a massive change indeed :/ > Anyway: >=20 > Reviewed-by: Andrzej Hajda I assume you'll want me to hold off that patch before someone reviews the rest? Thanks! Maxime --6br4ofwy642o3hq4 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYUCzPQAKCRDj7w1vZxhR xZX4AQCpuzsltUoIAMTseQh0blWKIJdfpCQSgO0Tdf29VLbP8gEAx8aZkhD8UtLs gYRcFQgX4NWKsoez7eyiExM4WOxRygQ= =zKFO -----END PGP SIGNATURE----- --6br4ofwy642o3hq4--