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SubjectRe: [PATCH] tpm/tpm_tis: Fix variable reset during IRQ probing
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On 1/14/21 10:51 AM, Jarkko Sakkinen wrote:
> On Wed, Jan 13, 2021 at 08:00:21PM +0800, Tianjia Zhang wrote:
>> In tpm_tis_core_init(), tpm2_probe() will be called first, this
>> function will eventually call tpm_tis_send(), and then
>> tpm_tis_probe_irq_single() will detect whether the interrupt is
>> normal, mainly the installation interrupted, set `priv->irq_tested`
>> to false. The logic will eventually be executed to tpm_tis_send()
>> to trigger an interrupt.
>>
>> There is currently such a scenario, which will cause the IRQ probe
>> code to never be executed, so that the TPM device is in polling
>> mode: after setting irq_tested to false, an interrupt occurs
>> between entering the ttpm_tis_send() function, and the interrupt
>> will be first set irq_tested to true will cause the IRQ probe code
>> to never be executed.
>
> Can you describe the scenario more detail?
>

The problematic scenario we encountered is like this. The following
figure shows the execution flow of tpm_tis_core_init(). An interrupt
occurred before the IRQ probe. This interrupt was caused by
tpm2_probe(), but it was triggered before the IRQ probe was executed,
and the interrupt handler would set irq_tested to true, so the IRQ probe
code can never execute, that is, the code marked 2 in the figure will
never happen.

IRQ
tpm_tis_core_init()

tpm2_probe()

tpm_tis_send() -----------+
|
tpm_tis_probe_irq_single() |
|
devm_request_irq() | 1
priv->irq_tested = false |
tpm_tis_gen_interrupt() |
|
tpm_tis_send() |
irq_tested = true |
<------------------+
if (priv->irq_tested)
return tpm_tis_send_main()

/* probe IRQ */
tpm_tis_send_main() --------+
| 2
chip->flags |= FLAG_IRQ <-------+
priv->irq_tested = true

Best regards,
Tianjia

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