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Wed, 22 Sep 2021 04:57:10 -0400 (EDT) Date: Wed, 22 Sep 2021 10:57:07 +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: <20210922085707.dr3fautmyowof7cr@gilmour> References: <20210910101218.1632297-1-maxime@cerno.tech> <20210910101218.1632297-3-maxime@cerno.tech> <7ad18d53-3ad6-a614-a8e1-cce6505f90a8@samsung.com> <20210914143541.433ucx2kvz36tw42@gilmour> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ogv2yceu2bvyarnp" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org --ogv2yceu2bvyarnp Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Tue, Sep 14, 2021 at 09:00:28PM +0200, Andrzej Hajda wrote: >=20 > W dniu 14.09.2021 o=A016:35, Maxime Ripard pisze: > > Hi, > > > > On Mon, Sep 13, 2021 at 08:29:37AM +0200, Andrzej Hajda wrote: > >> 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 ne= ed > >>> 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/gp= u/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_bridg= e.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 so= me > >>> + * point and the upstream driver should try to probe again by retu= rning > >>> + * 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 dis= play > >>> + * 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 operati= ons. > >>> + * 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 pr= obe > >>> + * of the bridge and upstream drivers, so care must be taken to av= oid > >>> + * 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 t= he > >>> + * MIPI-DSI host driver case) is to split the operations like this: > >>> + * > >>> + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in i= ts > >>> + * probe hook. It will make sure that the MIPI-DSI host sticks aro= und, > >>> + * 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 dev= ice > >>> + * to its host. The bridge driver is now functional. > >>> + * > >>> + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host= can > >>> + * now add its component. Its bind hook will now be called and sin= ce > >>> + * the bridge driver is attached and registered, we can now look f= or > >>> + * 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); > >> > >> Nice work with documenting this initialization dance. It clearly shows > >> that bridge API lacks better mechanism - usage of mipi dsi callbacks to > >> 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: > >> > >> Reviewed-by: Andrzej Hajda > > I assume you'll want me to hold off that patch before someone reviews > > the rest? >=20 > The last exynos patch should be dropped, Done > kirin patch should be tested/reviewed/acked by kirin maintaner. I am > not sure about bridge patches, which ones have been tested by you, and > which one have other users. Rob was nice enough to give it a try last week for msm and do the needed changes. He tested it with the sn65dsi86 bridge. John was also saying it was on their todo list (for kirin I assume?). So hopefully it can be fairly smooth for everyone. I tested sn65dsi83 and ps8640 with the vc4 driver. I don't have the hardware so it was just making sure that everything was probing properly, but it's what we're interested in anyway. > If yes it would be good to test them as well - changes in initialization= =20 > flow can beat sometimes :) >=20 > I think patches 1-4 can be merged earlier, if you like, as they are on=20 > the list for long time. Ack, I'll merge them, thanks! Maxime --ogv2yceu2bvyarnp Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYUrv4wAKCRDj7w1vZxhR xQoBAP920qamAHvLMhCg5u1wp+EEFBEufqValUOHaOJZojlTCwEA/7pqFJGHB8T3 DdmJKwivFSWQ4kYOXp5/PsK5KM2l7wM= =MG4a -----END PGP SIGNATURE----- --ogv2yceu2bvyarnp--