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i2c_smbus_write_block_data vs scheduled routine calls (add_timer) - kernel crash

DISCUSSION NiTr0 3 participants 3 messages Aug 4, 2009 1 message not in the archive I2C subsystem host drivers

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NiTr0

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#0 lore raw

I tried to improve voltage/FSB manipulation module for EeePC (http://code.google.com/p/eeepc-linux) - and I found that i2c_smbus_write_block_data will cause kernel panic when is called from function called by timer. I can't see kernel panic message because system print very long call trace. Also on EeePC there is no RS232 port - but I have USB->RS232 dongle, can it be used as terminal for debug messages?

All variables are declared as static, all data is prepared correctly - so IMHO trouble is outside of my driver. There is a part of code:

static struct i2c_client eee_pll_smbus_client = {
       .adapter = NULL,
       .addr = 0x69,
       .flags = 0,
};
static char eee_pll_data[I2C_SMBUS_BLOCK_MAX];
static int eee_pll_datalen = 0;
.......................
       i2c_smbus_write_block_data(&eee_pll_smbus_client,0,

eee_pll_datalen, eee_pll_data);

A message that is not in the archive (sent off-list or not yet received): [email protected]

#2 lore raw

El Tue, Aug 04, 2009 at 09:42:41PM +0300 NiTr0 ha dit:

Quoted 21 lines

I tried to improve voltage/FSB manipulation module for EeePC
(http://code.google.com/p/eeepc-linux) - and I found that i2c_smbus_write_block_data will cause kernel panic when is called from function called by timer. I can't see kernel panic message because system print very long call trace. Also on EeePC there is no RS232 port
- but I have USB->RS232 dongle, can it be used as terminal for debug messages?

All variables are declared as static, all data is prepared correctly - so IMHO trouble is outside of my driver.
There is a part of code:

static struct i2c_client eee_pll_smbus_client = {
       .adapter = NULL,
       .addr = 0x69,
       .flags = 0,
};
static char eee_pll_data[I2C_SMBUS_BLOCK_MAX];
static int eee_pll_datalen = 0;
.......................
       i2c_smbus_write_block_data(&eee_pll_smbus_client,0,
Quoted 1 line

eee_pll_datalen, eee_pll_data);

a possible source of problems is that i2c_smbus_xfer() (invoked by i2c_smbus_write_block_data()) tries to aquire a mutex if adapter->algo->smbus_xfer is set.

http://lxr.linux.no/linux+v2.6.30/drivers/i2c/i2c-core.c#L1994

timers are executed in a softirq, ie in interrupt context, but mutexes must not be used within interrupts.

i'm neither an i2c-core nor an kernel expert, but this point looks conflictive to me and might be the reason for the kernel panic you get.

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Matthias Kaehlcke
Embedded Linux Engineer
Barcelona

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#3 lore raw
In reply to a message not in the archive
Quoted 3 lines · On Tue, Aug 04, 2009 at 09:42:41PM +0300, NiTr0 wrote:

All variables are declared as static, all data is prepared correctly
- so IMHO trouble is outside of my driver.
There is a part of code:

The problem is that your driver is trying to do I2C/SMBus I/O from a timer, which is run from an interrupt context. Since I2C buses are generally very slow the controllers are interrupt driven and the read and write operations on them will sleep waiting for operations to complete. If the code waited for the I/O to complete in an interrupt context it would cause serious performance problems in the rest of the system.

You should do the actual I/O from another context, such as a workqueue. schedule_delayed_work() may be helpful here.