[PATCH v3 3/3] common: Move autoprobe out to board init

[Simon Glass]

Rather than doing autoprobe within the driver model code, move it out to
the board-init code. This makes it clear that it is a separate step from
binding devices.

For now this is always done twice, before and after relocation, but we
should discuss whether it might be possible to drop the post-relocation
probe.

For boards with SPL, the autoprobe is still done there as well.

Note that with this change, autoprobe happens after the
EVT_DM_POST_INIT_R/F events are sent, rather than before.

Link: https://lore.kernel.org/u-boot/20240626235717.272219-1-marex@denx.de/

Signed-off-by: Simon Glass <sjg at chromium.org>
---

Changes in v3:
- Add a link to the previous discussion
- Add a summary of the design challenge in the DM docs
- Use a simple return in initr_dm()
- Add a comment to dm_probe_devices()
- Expand comment to dm_autoprobe()

Changes in v2:
- Add autoprobe to SPL also
- Leave the function name the same
- Fix 'Prove' typo
- Update cover letter since SPL is now covered also
- Update the documentation too, with a discussion link

 common/board_f.c                    |  4 ++++
 common/board_r.c                    |  2 +-
 common/spl/spl.c                    |  4 ++++
 doc/develop/driver-model/design.rst | 17 +++++++++++++++++
 drivers/core/root.c                 | 22 +++++++++++++++++++++-
 include/dm/root.h                   | 15 +++++++++++++++
 6 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/common/board_f.c b/common/board_f.c
index 1e1aa08530a..974eb4f39e9 100644
--- a/common/board_f.c
+++ b/common/board_f.c
@@ -822,6 +822,10 @@ static int initf_dm(void)
 	if (ret)
 		return ret;
 
+	ret = dm_autoprobe();
+	if (ret)
+		return ret;
+
 	if (IS_ENABLED(CONFIG_TIMER_EARLY)) {
 		ret = dm_timer_init();
 		if (ret)
diff --git a/common/board_r.c b/common/board_r.c
index 62228a723e1..b761833294f 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -241,7 +241,7 @@ static int initr_dm(void)
 	if (ret)
 		return ret;
 
-	return 0;
+	return dm_autoprobe();
 }
 #endif
 
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 1ceb63daf31..c4256f237ee 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -500,6 +500,10 @@ static int spl_common_init(bool setup_malloc)
 			debug("dm_init_and_scan() returned error %d\n", ret);
 			return ret;
 		}
+
+		ret = dm_autoprobe();
+		if (ret)
+			return ret;
 	}
 
 	return 0;
diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst
index 8c2c81d7ac9..92f638a0204 100644
--- a/doc/develop/driver-model/design.rst
+++ b/doc/develop/driver-model/design.rst
@@ -842,6 +842,23 @@ steps (see device_probe()):
       cause the uclass to do some housekeeping to record the device as
       activated and 'known' by the uclass.
 
+For some platforms, certain devices must be probed to get the platform into
+a working state. To help with this, drivers marked with DM_FLAG_PROBE_AFTER_BIND
+will be probed immediately after all devices are bound. For now, this happens in
+SPL, before relocation and after relocation. See the call to ``dm_autoprobe()``
+for where this is done.
+
+The auto-probe feature is tricky because it bypasses the normal ordering of
+probing. General, if device A (e.g. video) needs device B (e.g. clock), then
+A's probe() method uses ``clk_get_by_index()`` and B is probed before A. But
+A is only probed when it is used. Therefore care should be taken when using
+auto-probe, limiting it to devices which truly are essential, such as power
+domains or critical clocks.
+
+See here for more discussion of this feature:
+
+:Link: https://patchwork.ozlabs.org/project/uboot/patch/20240626235717.272219-1-marex@denx.de/
+
 Running stage
 ^^^^^^^^^^^^^
 
diff --git a/drivers/core/root.c b/drivers/core/root.c
index 2d4f078f97f..045f8fcda65 100644
--- a/drivers/core/root.c
+++ b/drivers/core/root.c
@@ -281,6 +281,15 @@ void *dm_priv_to_rw(void *priv)
 }
 #endif
 
+/**
+ * dm_probe_devices() - Check whether to probe a device and all children
+ *
+ * Probes the device if DM_FLAG_PROBE_AFTER_BIND is enabled for it. Then scans
+ * all its children recursively to do the same.
+ *
+ * @dev: Device to (maybe) probe
+ * Return 0 if OK, -ve on error
+ */
 static int dm_probe_devices(struct udevice *dev)
 {
 	struct udevice *child;
@@ -299,6 +308,17 @@ static int dm_probe_devices(struct udevice *dev)
 	return 0;
 }
 
+int dm_autoprobe(void)
+{
+	int ret;
+
+	ret = dm_probe_devices(gd->dm_root);
+	if (ret)
+		return log_msg_ret("pro", ret);
+
+	return 0;
+}
+
 /**
  * dm_scan() - Scan tables to bind devices
  *
@@ -331,7 +351,7 @@ static int dm_scan(bool pre_reloc_only)
 	if (ret)
 		return ret;
 
-	return dm_probe_devices(gd->dm_root);
+	return 0;
 }
 
 int dm_init_and_scan(bool pre_reloc_only)
diff --git a/include/dm/root.h b/include/dm/root.h
index b2f30a842f5..a71a2ebef85 100644
--- a/include/dm/root.h
+++ b/include/dm/root.h
@@ -136,6 +136,21 @@ int dm_scan_other(bool pre_reloc_only);
  */
 int dm_init_and_scan(bool pre_reloc_only);
 
+/**
+ * dm_autoprobe() - Probe devices which are marked for probe-after-bind
+ *
+ * This probes all devices with a DM_FLAG_PROBE_AFTER_BIND flag. It checks the
+ * entire tree, so parent nodes need not have the flag set.
+ *
+ * It recursively probes parent nodes, so they do not need to have the flag
+ * set themselves. Since parents are always probed before children, if a child
+ * has the flag set, then its parent (and any devices up the chain to the root
+ * device) will be probed too.
+ *
+ * Return: 0 if OK, -ve on error
+ */
+int dm_autoprobe(void);
+
 /**
  * dm_init() - Initialise Driver Model structures
  *
-- 
2.34.1