From: Maxime Ripard <maxime@cerno.tech>
To: Andrzej Hajda <a.hajda@samsung.com>,
Sam Ravnborg <sam@ravnborg.org>,
Daniel Vetter <daniel.vetter@intel.com>,
David Airlie <airlied@linux.ie>, Jonas Karlman <jonas@kwiboo.se>,
Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
Thierry Reding <thierry.reding@gmail.com>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Thomas Zimmermann <tzimmermann@suse.de>,
Maxime Ripard <maxime@cerno.tech>,
Neil Armstrong <narmstrong@baylibre.com>,
Robert Foss <robert.foss@linaro.org>,
Jernej Skrabec <jernej.skrabec@gmail.com>
Cc: Sean Paul <sean@poorly.run>,
freedreno@lists.freedesktop.org,
Kyungmin Park <kyungmin.park@samsung.com>,
linux-kernel@vger.kernel.org,
Xinliang Liu <xinliang.liu@linaro.org>,
Seung-Woo Kim <sw0312.kim@samsung.com>,
Tian Tao <tiantao6@hisilicon.com>,
Inki Dae <inki.dae@samsung.com>,
linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org,
Rob Clark <robdclark@gmail.com>,
dri-devel@lists.freedesktop.org,
John Stultz <john.stultz@linaro.org>,
Chen Feng <puck.chen@hisilicon.com>,
Xinwei Kong <kong.kongxinwei@hisilicon.com>,
Joonyoung Shim <jy0922.shim@samsung.com>
Subject: [PATCH v4 02/24] drm/bridge: Document the probe issue with MIPI-DSI bridges
Date: Fri, 10 Sep 2021 12:11:56 +0200 [thread overview]
Message-ID: <20210910101218.1632297-3-maxime@cerno.tech> (raw)
In-Reply-To: <20210910101218.1632297-1-maxime@cerno.tech>
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 <maxime@cerno.tech>
---
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
+Special Care with MIPI-DSI bridges
+----------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
+ :doc: special care dsi
+
Bridge Operations
-----------------
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).
*/
+/**
+ * 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 returning
+ * 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 display
+ * 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 operations.
+ * 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 around,
+ * 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 can
+ * 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);
--
2.31.1
next prev parent reply other threads:[~2021-09-10 10:12 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-10 10:11 [PATCH v4 00/24] drm/bridge: Make panel and bridge probe order consistent Maxime Ripard
2021-09-10 10:11 ` [PATCH v4 01/24] drm/bridge: Add documentation sections Maxime Ripard
2021-09-24 17:52 ` (subset) " Maxime Ripard
2021-09-10 10:11 ` Maxime Ripard [this message]
2021-09-13 6:29 ` [PATCH v4 02/24] drm/bridge: Document the probe issue with MIPI-DSI bridges Andrzej Hajda
2021-09-14 14:35 ` Maxime Ripard
2021-09-14 19:00 ` Andrzej Hajda
2021-09-22 8:57 ` Maxime Ripard
2021-09-24 17:52 ` (subset) " Maxime Ripard
2021-09-10 10:11 ` [PATCH v4 03/24] drm/mipi-dsi: Create devm device registration Maxime Ripard
2021-09-24 17:52 ` (subset) " Maxime Ripard
2021-09-10 10:11 ` [PATCH v4 04/24] drm/mipi-dsi: Create devm device attachment Maxime Ripard
2021-09-24 17:52 ` (subset) " Maxime Ripard
2021-09-10 10:11 ` [PATCH v4 05/24] drm/bridge: adv7533: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 06/24] drm/bridge: adv7511: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 07/24] drm/bridge: anx7625: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 08/24] drm/bridge: anx7625: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 09/24] drm/bridge: lt8912b: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 10/24] drm/bridge: lt8912b: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 11/24] drm/bridge: lt9611: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 12/24] drm/bridge: lt9611: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 13/24] drm/bridge: lt9611uxc: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 14/24] drm/bridge: lt9611uxc: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 15/24] drm/bridge: ps8640: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 16/24] drm/bridge: ps8640: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 17/24] drm/bridge: sn65dsi83: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 18/24] drm/bridge: sn65dsi83: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 19/24] drm/bridge: sn65dsi86: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 20/24] drm/bridge: sn65dsi86: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 21/24] drm/bridge: tc358775: Switch to devm MIPI-DSI helpers Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 22/24] drm/bridge: tc358775: Register and attach our DSI device at probe Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 23/24] drm/kirin: dsi: Adjust probe order Maxime Ripard
2021-09-10 10:12 ` [PATCH v4 24/24] drm/exynos: " Maxime Ripard
2021-09-13 10:30 ` Andrzej Hajda
2021-09-17 12:35 ` Marek Szyprowski
2021-09-22 8:53 ` Maxime Ripard
2021-09-23 8:14 ` Marek Szyprowski
2021-09-29 21:27 ` [PATCH v4 00/24] drm/bridge: Make panel and bridge probe order consistent John Stultz
2021-09-29 21:32 ` John Stultz
2021-09-29 21:51 ` John Stultz
2021-09-29 23:25 ` Rob Clark
2021-09-29 23:25 ` John Stultz
2021-09-30 2:30 ` John Stultz
2021-09-30 19:49 ` Amit Pundir
2021-09-30 20:20 ` Caleb Connolly
2021-10-13 14:16 ` Maxime Ripard
2021-10-14 0:16 ` [Freedreno] " Rob Clark
2021-10-18 12:34 ` Maxime Ripard
2021-10-18 15:55 ` Rob Clark
2021-09-29 23:29 ` John Stultz
2021-10-13 13:45 ` Maxime Ripard
2021-09-29 21:56 ` Laurent Pinchart
2021-10-03 13:25 ` Laurent Pinchart
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