Re: More interrupt problems with TIS TPM

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Sep 28, 2020 at 05:52:43PM -0700, James Bottomley wrote:
> I've got hold of an infineon TIS TPM which actually has a working
> interrupt.  I find even with the other fix I still need the patch below
> to get the interrupt to fire because without it nothing ever sets
> TPM_CHIP_FLAG_IRQ which means the interrupt test code is never
> executed.
> 
> Finally with all this probing fixed, I'm seeing interrupt storms.  The
> way this TPM seems to work is that if you allow it to send command
> ready interrupts, it will send them any time it can accept a command. 
> The problem is if you clear the interrupt and it can accept a command,
> it will send another command ready interrupt ... hence the storm since
> the TPM is pretty much always in the command ready state.  The only way
> to mitigate this seems to be *only* to enable the command ready
> interrupt when you're preparing to wait for the TPM to become ready. 
> i.e. these interrupts have to be treated as one shot enable, so the
> interrupt routine has to mask the command ready interrupt before doing
> a TPM_EOI in our way of doing things.  There seems to be support for
> this in the TIS spec around line 1135 where it advises us to keep all
> interrupts masked until polling says we have to wait for a particular
> state.
> 
> James

OK, this makes a lot of sense. I'll go through the patch set that you
posted. Thank you.

> 
> ---
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 6b884badabe7..1578d158416c 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -804,6 +810,7 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
>  		return rc;
>  
>  	priv->irq_tested = false;
> +	chip->flags |= TPM_CHIP_FLAG_IRQ;
>  
>  	/* Generate an interrupt by having the core call through to
>  	 * tpm_tis_send
> 
> 

/Jarkko