[PATCH v2] PM: runtime: Update runtime_pm.rst for non-fatal resume errors

[Stanley Jhu <stanleyjhu@google.com>]

Since commit eef1d74bf88f ("PM: runtime: Only set runtime_error on
suspend callback failures"), rpm_callback() no longer sets
dev->power.runtime_error when ->runtime_resume() returns an error.
However, Documentation/power/runtime_pm.rst still states in both the
resume callback rules and the ->runtime_idle() comparison that the PM
core treats ->runtime_resume() errors as fatal device errors and blocks
runtime PM helper functions until the status is manually reset.

Update the resume callback semantics bullet to state that on error the
PM core resets the runtime PM status to 'suspended', returns the error
code from synchronous resume helpers, and unlike with the suspend
callback never treats resume failures as fatal, leaving the Section 4
runtime PM helpers unblocked so a subsequent resume request can run
->runtime_resume() again. Also drop ->runtime_resume() from the
->runtime_idle() fatal-error comparison.

Fixes: eef1d74bf88f ("PM: runtime: Only set runtime_error on suspend callback failures")
Fixes: aedc51762a0d ("PM: runtime: Clarify ->runtime_idle() callback return value handling")
Signed-off-by: Stanley Jhu <stanleyjhu@google.com>
---
Differences from v1:
- Contrast resume failures with the suspend callback instead of citing
  -EBUSY, -EAGAIN, or power.runtime_error (Brian Norris)
- Add Fixes tag for commit aedc51762a0d covering ->runtime_idle()
- Link to v1: https://lore.kernel.org/r/20261029040005.2100005-1-stanleyjhu@google.com

 Documentation/power/runtime_pm.rst | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
index 40a5c23d5259..09072c576087 100644
--- a/Documentation/power/runtime_pm.rst
+++ b/Documentation/power/runtime_pm.rst
@@ -222,11 +222,12 @@ what to do to handle the device).
     I/O operations as needed.  The runtime PM status of the device is then
     'active'.
 
-  * If the resume callback returns an error code, the PM core regards this as a
-    fatal error and will refuse to run the helper functions described in
-    `Section 4`_ for the device, until its status is directly set to either
-    'active', or 'suspended' (by means of special helper functions provided by
-    the PM core for this purpose).
+  * If the resume callback returns an error code, the PM core sets the
+    device's runtime PM status back to 'suspended' and returns the error
+    code from synchronous resume helpers.  Unlike with the suspend
+    callback, failures in the resume callback are never considered fatal,
+    so the helper functions described in `Section 4`_ are not blocked and
+    a subsequent resume request can run the resume callback again.
 
 The idle callback (a subsystem-level one, if present, or the driver one) is
 executed by the PM core whenever the device appears to be idle, which is
@@ -250,9 +251,9 @@ call to pm_runtime_autosuspend().
 To prevent this suspension (for example, if the callback routine has scheduled
 a delayed suspend or determined the device cannot be idle), the routine must
 return a non-zero value (typically -EBUSY or -EAGAIN).  Unlike
-->runtime_suspend() and ->runtime_resume(), the PM core does not treat negative
-return codes from ->runtime_idle() as a fatal device error; any non-zero value
-simply stops the PM core from suspending the device.
+->runtime_suspend(), the PM core does not treat negative return codes from
+->runtime_idle() as a fatal device error, and any non-zero value simply stops
+the PM core from suspending the device.
 
 Core Guarantees and Synchronization Rules
 -----------------------------------------
-- 
2.56.0.385.gac671c819a-goog