On 6/24/24 01:38, Krzysztof Olędzki wrote:
On 23.06.2024 at 22:33, Guenter Roeck wrote:
On 6/23/24 11:47, Krzysztof Olędzki wrote:
Hi,
After upgrading kernel to Linux 6.6.34 on one of my systems, I noticed "sysfs: cannot create duplicate filename" and i2c registration errors in dmesg, please see below.
This seems to be related to https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-6.6.y&id=4d5ace787273cb159bfdcf1c523df957938b3e42 - reverting the change fixes the problem.
Note that jc42 devices are registered correctly and work with and without the change.
My guess is that the devices are fist instantiated through the jc42
driver's _detect function and then again from the at24 driver.
The at24 driver should possibly call i2c_new_scanned_device() instead
of i2c_new_client_device() to only instantiate the device if it wasn't
already instantiated.
i2c_new_scanned_device() also calls i2c_default_probe() at the end (unless
different probe is provided) which seems risky given the comment that explains
that it would use quick write for that address. However, maybe it is safe in this case?
I wish we had a way to just tell "no probing is needed".
Sorry, I don't understand why it would be less risky to just probe the device
without such a test.
We also know the exact address so no scanning is needed.
Perhaps it would be better to just call i2c_check_addr_busy() in
at24_probe_temp_sensor()?
Something like this:
--- a/drivers/misc/eeprom/at24.c 2024-06-24 09:16:11.251855130 +0200
+++ b/drivers/misc/eeprom/at24.c 2024-06-24 09:27:01.158170725 +0200
@@ -603,6 +603,10 @@
info.addr = 0x18 | (client->addr & 7);
+ /* The device may be already instantiated through the jc42 driver */
+ if (i2c_check_addr_busy(client->adapter, info.addr))
+ return;
+
i2c_new_client_device(client->adapter, &info);
}
Unfortunately, i2c_check_addr_busy is not exported and declared as static,
That is why I did not suggest that.
I assume intentionally? Unless this can be changed, we are back to the original
recommendation:
--- a/drivers/misc/eeprom/at24.c 2024-06-24 09:16:11.251855130 +0200
+++ b/drivers/misc/eeprom/at24.c 2024-06-24 10:25:39.142567472 +0200
@@ -585,6 +585,7 @@
{
struct at24_data *at24 = i2c_get_clientdata(client);
struct i2c_board_info info = { .type = "jc42" };
+ unsigned short addr_list[] = { 0, I2C_CLIENT_END };
int ret;
u8 val;
@@ -601,9 +602,10 @@
if (ret || !(val & BIT(7)))
return;
- info.addr = 0x18 | (client->addr & 7);
+ addr_list[0] = 0x18 | (client->addr & 7);
- i2c_new_client_device(client->adapter, &info);
+ /* The device may be already instantiated through the jc42 driver */
+ i2c_new_scanned_device(client->adapter, &info, addr_list, NULL);
}
static int at24_probe(struct i2c_client *client)
For now compile-tested only given the write-test concern above.
The device detect code in the i2c core does that same write-test that you
are concerned about.
That said, I have some follow-up questions:
1. if the jc42 driver handles this already, I wonder what's the point of adding
at24_probe_temp_sensor()? Is there a situation where it would not do it properly?
Or do we expect to remove the probing functionally from jc42.c?
The jc42 driver is not auto-loaded. When suggesting to remove the "probing
functionally", I assume you mean to remove its detect function. That would only
work if SPD EEPROMs were only connected to I2C adapters calling i2c_register_spd(),
and if the systems with those adapters would support DMI.
In v6.9, i2c_register_spd() is only called from the i801 driver (Intel systems).
In v6.11, piix4 (AMD) will be added. Even after that, all non-Intel / non-AMD systems
would no longer be able to support jc42 compatible chips by just loading the jc42
driver. That would not be acceptable.
2. I don't understand why we are also getting the "Failed creating jc42" and
"sysfs: cannot create duplicate filename" errors since i2c_new_client_device() calls
i2c_check_addr_busy() on its own and should abort after the first error message?
The "Failed creating" message is from the i2c core's detect function which
is only called if a new i2c adapter is added. This is actually the case here,
since the call sequence of the backtrace includes i801_probe(). It looks like
i2c_detect() runs asynchronously and doesn't protect itself against having
devices added to a bus while it is running on that same bus. That is just
a guess, though - I have not tried to verify it.
That does suggest, though, that even your suggested code above might not
completely fix the problem. It may be necessary to call i2c_lock_bus()
or similar from i2c_new_scanned_device() and i2c_detect(), but I don't know
if that is save, sufficient, or even possible.
3. (unrelated but found while looking at the code) The comment for
delete_device_store() seems to be outdated as it mentions i2c_sysfs_new_device
which does not exist any longer, as it was renamed in
"i2c: core: Use DEVICE_ATTR_*() helper macros" back in 2019:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/i2c/i2c-core-base.c?id=54a19fd4a6402ef47fce5c3a5374c71f52373c40 -
For the Greg's question if it is also in 6.9: I have not tested that kernel yet,
but unless there have been some recent changes in the i2c code I would expect
it should behave the same way. If required, I should be able to do this next week.
Agreed.
Guenter
