From: Jerry Lv Jerry.Lv@axis.com
[ Upstream commit f16d9fb6cf03fdbdefa41a8b32ba1e57afb7ae3d ]
Multiple applications may access the battery gauge at the same time, so the gauge may be busy and EBUSY will be returned. The driver will set a flag to record the EBUSY state, and this flag will be kept until the next periodic update. When this flag is set, bq27xxx_battery_get_property() will just return ENODEV until the flag is updated.
Even if the gauge was busy during the last accessing attempt, returning ENODEV is not ideal, and can cause confusion in the applications layer.
Instead, retry accessing the I2C to update the flag is as expected, for the gauge typically recovers from busy state within a few milliseconds. If still failed to access the gauge, the real error code would be returned instead of ENODEV (as suggested by Pali Rohár).
Reviewed-by: Pali Rohár pali@kernel.org Signed-off-by: Jerry Lv Jerry.Lv@axis.com Link: https://lore.kernel.org/r/20250415-foo-fix-v2-1-5b45a395e4cc@axis.com Signed-off-by: Sebastian Reichel sebastian.reichel@collabora.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. ## Detailed Analysis: ### 1. **User-Visible Bug Fix** ✅ The commit fixes a clear user-visible issue where multiple applications accessing the battery gauge simultaneously receive confusing `-ENODEV` errors instead of actual battery data or proper error codes. This directly impacts battery monitoring applications and system power management tools. ### 2. **Code Changes Analysis** **bq27xxx_battery.c change:** ```c -return -ENODEV; +return di->cache.flags; ``` This single-line change stops masking real error codes with generic `-ENODEV`, allowing applications to see the actual error (like `-EBUSY`) and handle it appropriately. **bq27xxx_battery_i2c.c changes:** - Adds retry logic with up to 3 attempts when encountering `-EBUSY` - Uses standard `usleep_range(10000, 11000)` for 10ms delays - Implements proper loop structure with explicit break conditions ### 3. **Small and Contained** ✅ The changes are minimal and focused: - No architectural modifications - No changes to driver interfaces or APIs - Limited to error handling improvement within the same subsystem ### 4. **Low Regression Risk** ✅ - Uses established kernel patterns (`usleep_range`, retry counters) - No timing changes to critical paths - Battery gauges typically recover from busy state within milliseconds - Maintains backward compatibility ### 5. **Historical Precedent** ✅ Analysis of similar bq27xxx commits shows consistent backporting: - "Fix race condition" (Similar Commit #4): **YES** - Similar I2C access improvement - "After charger plug in/out wait 0.5s" (Similar Commit #5): **YES** - Similar stability fix - "make status more robust" (Similar Commit #2): **YES** - Similar robustness improvement ### 6. **Follows Kernel Conventions** ✅ - Standard I2C retry mechanisms are common in the kernel - Proper error code propagation instead of masking - Code reviewed by subsystem maintainer (Pali Rohár) - Uses kernel-standard delay functions ### 7. **System Impact** **Improves stability** by: - Preventing userspace confusion from misleading error codes - Gracefully handling concurrent access scenarios - Better error reporting for debugging - No negative side effects identified ### 8. **Risk Assessment** **Very Low Risk:** - No memory management changes - No locking mechanism modifications - Standard retry pattern with bounded attempts - Preserves all existing functionality This commit represents an ideal stable backport candidate: it fixes a real user-visible bug with minimal, well-understood code changes that follow established kernel patterns and have strong historical precedent for backporting in this driver subsystem.
drivers/power/supply/bq27xxx_battery.c | 2 +- drivers/power/supply/bq27xxx_battery_i2c.c | 13 ++++++++++++- 2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c index 23c8736567574..e51fa2c694bc6 100644 --- a/drivers/power/supply/bq27xxx_battery.c +++ b/drivers/power/supply/bq27xxx_battery.c @@ -2044,7 +2044,7 @@ static int bq27xxx_battery_get_property(struct power_supply *psy, mutex_unlock(&di->lock);
if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0) - return -ENODEV; + return di->cache.flags;
switch (psp) { case POWER_SUPPLY_PROP_STATUS: diff --git a/drivers/power/supply/bq27xxx_battery_i2c.c b/drivers/power/supply/bq27xxx_battery_i2c.c index 886e0a8e2abd1..8877fa333cd02 100644 --- a/drivers/power/supply/bq27xxx_battery_i2c.c +++ b/drivers/power/supply/bq27xxx_battery_i2c.c @@ -6,6 +6,7 @@ * Andrew F. Davis afd@ti.com */
+#include <linux/delay.h> #include <linux/i2c.h> #include <linux/interrupt.h> #include <linux/module.h> @@ -32,6 +33,7 @@ static int bq27xxx_battery_i2c_read(struct bq27xxx_device_info *di, u8 reg, struct i2c_msg msg[2]; u8 data[2]; int ret; + int retry = 0;
if (!client->adapter) return -ENODEV; @@ -48,7 +50,16 @@ static int bq27xxx_battery_i2c_read(struct bq27xxx_device_info *di, u8 reg, else msg[1].len = 2;
- ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); + do { + ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); + if (ret == -EBUSY && ++retry < 3) { + /* sleep 10 milliseconds when busy */ + usleep_range(10000, 11000); + continue; + } + break; + } while (1); + if (ret < 0) return ret;