linux-kernel - Re: question about setting TPM_CHIP_FLAG_IRQ in tpm_tis_core

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Date:   Tue, 12 Nov 2019 15:30:51 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: question about setting TPM_CHIP_FLAG_IRQ in tpm_tis_core_init

On 11/12/19 3:17 PM, Jerry Snitselaar wrote:
> On Tue Nov 12 19, Jarkko Sakkinen wrote:
>> On Mon, Nov 11, 2019 at 08:36:37PM -0700, Jerry Snitselaar wrote:
>>> Question about 1ea32c83c699 ("tpm_tis_core: Set TPM_CHIP_FLAG_IRQ
>>> before probing for interrupts").  Doesn't tpm_tis_send set this flag,
>>> and setting it here in tpm_tis_core_init short circuits what
>>> tpm_tis_send was doing before? There is a bug report of an interrupt
>>> storm from a tpm on a t490s laptop with the Fedora 31 kernel (5.3),
>>> and I'm wondering if this change could cause that. Before they got the
>>> warning about interrupts not working, and using polling instead.
>>
>> Looks like it. Stefan?
>>
>> /Jarkko
>>
>
> Stefan is right about the condition check at the beginning of 
> tpm_tis_send.
>
>     if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
>         return tpm_tis_send_main(chip, buf, len);
>
> Before his change it would've gone straight to calling
> tpm_tis_send_main instead of jumping down and doing the irq test, due
> to the flag not being set. With his change it should now skip this
> tpm_tis_send_main call when tpm_tis_gen_interrupt is called, and then
> after that time through tpm_tis_send priv->irq_tested will be set, and
> the flag should be set as to whether or not irqs were working.
>
> I should hopefully have access to a t490s in a few days so I can look 
> at it,
> and try to figure out what is happening.
>
I hope the t490s is an outlier. Give the patch I just posted a try.

     Stefan