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

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Date:   Tue, 12 Nov 2019 08:28:57 -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 11/11/19 10:36 PM, 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.
>
I set this flag for the TIS because it wasn't set anywhere else. 
tpm_tis_send() wouldn't set the flag but go via the path:

if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)

         return tpm_tis_send_main(chip, buf, len);

the only other line for the TIS to set the IRQ flag was in the same 
function further below, though that wouldn't be reached due to the above:

[...]

priv->irq = irq;

chip->flags |= TPM_CHIP_FLAG_IRQ;


    Stefan