Hi,
On 28.04.21 at 01:53, Jarkko Sakkinen wrote:
> On Mon, Apr 26, 2021 at 01:47:17AM +0200, Lino Sanfilippo wrote:
>> Interrupt handling at least includes reading and writing the interrupt
>> status register from the interrupt routine. However over SPI those accesses
>> require a sleepable context, since a mutex is used in the concerning
>> functions.
>> For this reason request a threaded interrupt handler which is running in
>> (sleepable) process context.
>>
>> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx>
>> ---
>> drivers/char/tpm/tpm_tis_core.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>> index e7d1eab..0959559 100644
>> --- a/drivers/char/tpm/tpm_tis_core.c
>> +++ b/drivers/char/tpm/tpm_tis_core.c
>> @@ -781,8 +781,10 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
>> int rc;
>> u32 int_status;
>>
>> - if (devm_request_irq(chip->dev.parent, irq, tis_int_handler, flags,
>> - dev_name(&chip->dev), chip) != 0) {
>> +
>> + if (devm_request_threaded_irq(chip->dev.parent, irq, NULL,
>> + tis_int_handler, IRQF_ONESHOT | flags,
>> + dev_name(&chip->dev), chip) != 0) {
>> dev_info(&chip->dev, "Unable to request irq: %d for probe\n",
>> irq);
>> return -1;
>> --
>> 2.7.4
>>
>
> Why?
>
> https://elixir.bootlin.com/linux/v5.12/source/drivers/char/tpm/tpm_tis_core.c#L670
>
> I don't see anything that sleeps there.
>
> /Jarkko1
>
The problem are the register read/write functions which we use to access the status register in
the interrupt handler. In case of SPI they result in taking the spi_bus_lock which is a mutex.
E.g tpm_tis_spi_read32: tpm_tis_spi_read_bytes->tpm_tis_spi_transfer->spi_bus_lock->mutex_lock
Using a threaded interrupt handler seemed to me the easiest way to avoid this issue.
Regards,
Lino
