[PATCH] misc: eeprom: at24: Make VCC supply description requirement optional
From: Paul Menzel <hidden>
Date: 2026-05-24 08:07:56
Also in:
linux-i2c, lkml
Subsystem:
at24 eeprom driver, char and misc drivers, the rest · Maintainers:
Bartosz Golaszewski, Arnd Bergmann, Greg Kroah-Hartman, Linus Torvalds
Some platforms (e.g. IBM Power System S822LC (8335-GCA POWER8)) do not
describe the EEPROM’s VCC supply in firmware-provided device trees.
Using `devm_regulator_get()` on such systems falls back to a dummy
regulator with a kernel warning:
at24 0-0051: supply vcc not found, using dummy regulator
at24 0-0051: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
at24 0-0052: supply vcc not found, using dummy regulator
at24 0-0052: 256 byte 24c02 EEPROM, writable, 1 bytes/write
at24 0-0053: supply vcc not found, using dummy regulator
at24 0-0053: 256 byte 24c02 EEPROM, writable, 1 bytes/write
at24 0-0054: supply vcc not found, using dummy regulator
at24 0-0054: 256 byte 24c02 EEPROM, writable, 1 bytes/write
[…]
at24 12-0050: supply vcc not found, using dummy regulator
at24 12-0050: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
at24 12-0051: supply vcc not found, using dummy regulator
at24 12-0051: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
Switch to `devm_regulator_get_optional()` and treat -ENODEV as “no
supply described”. When `vcc_reg` is NULL, skip all
regulator_enable/disable calls; the hardware is assumed to be always
powered. Linux now logs:
at24 0-0051: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
at24 0-0052: 256 byte 24c02 EEPROM, writable, 1 bytes/write
at24 0-0053: 256 byte 24c02 EEPROM, writable, 1 bytes/write
at24 0-0054: 256 byte 24c02 EEPROM, writable, 1 bytes/write
at24 0-0055: 256 byte 24c02 EEPROM, writable, 1 bytes/write
[…]
at24 12-0050: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
at24 12-0051: 16384 byte 24c128 EEPROM, writable, 1 bytes/write
Assisted-by: Claude Sonnet 4.6
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Paul Menzel <redacted>
---
drivers/misc/eeprom/at24.c | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 0200288d3a7a..7e1050f8759a 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c@@ -699,9 +699,12 @@ static int at24_probe(struct i2c_client *client) at24->offset_adj = at24_get_offset_adj(flags, byte_len); at24->client_regmaps[0] = regmap; - at24->vcc_reg = devm_regulator_get(dev, "vcc"); - if (IS_ERR(at24->vcc_reg)) - return PTR_ERR(at24->vcc_reg); + at24->vcc_reg = devm_regulator_get_optional(dev, "vcc"); + if (IS_ERR(at24->vcc_reg)) { + if (PTR_ERR(at24->vcc_reg) != -ENODEV) + return PTR_ERR(at24->vcc_reg); + at24->vcc_reg = NULL; + } writable = !(flags & AT24_FLAG_READONLY); if (writable) {
@@ -754,9 +757,12 @@ static int at24_probe(struct i2c_client *client) full_power = acpi_dev_state_d0(&client->dev); if (full_power) { - err = regulator_enable(at24->vcc_reg); - if (err) - return dev_err_probe(dev, err, "Failed to enable vcc regulator\n"); + if (at24->vcc_reg) { + err = regulator_enable(at24->vcc_reg); + if (err) { + return dev_err_probe(dev, err, "Failed to enable vcc regulator\n"); + } + } pm_runtime_set_active(dev); }
@@ -771,7 +777,7 @@ static int at24_probe(struct i2c_client *client) err = at24_read(at24, 0, &test_byte, 1); if (err) { pm_runtime_disable(dev); - if (!pm_runtime_status_suspended(dev)) + if (!pm_runtime_status_suspended(dev) && at24->vcc_reg) regulator_disable(at24->vcc_reg); return -ENODEV; }
@@ -808,7 +814,7 @@ static void at24_remove(struct i2c_client *client) pm_runtime_disable(&client->dev); if (acpi_dev_state_d0(&client->dev)) { - if (!pm_runtime_status_suspended(&client->dev)) + if (!pm_runtime_status_suspended(&client->dev) && at24->vcc_reg) regulator_disable(at24->vcc_reg); pm_runtime_set_suspended(&client->dev); }
@@ -819,6 +825,8 @@ static int __maybe_unused at24_suspend(struct device *dev) struct i2c_client *client = to_i2c_client(dev); struct at24_data *at24 = i2c_get_clientdata(client); + if (!at24->vcc_reg) + return 0; return regulator_disable(at24->vcc_reg); }
@@ -827,6 +835,8 @@ static int __maybe_unused at24_resume(struct device *dev) struct i2c_client *client = to_i2c_client(dev); struct at24_data *at24 = i2c_get_clientdata(client); + if (!at24->vcc_reg) + return 0; return regulator_enable(at24->vcc_reg); }
--
2.53.0