linux-kernel - Re: [PATCH] tpm: tis: Increase the default for timeouts B and C

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Message-ID: <Z-2ZC2Ew2EtNAW6-@kitsune.suse.cz>
Date: Wed, 2 Apr 2025 22:07:39 +0200
From: Michal Suchánek <msuchanek@...e.de>
To: Jonathan McDowell <noodles@...th.li>
Cc: Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>, linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: tis: Increase the default for timeouts B and C

On Wed, Apr 02, 2025 at 06:45:40PM +0100, Jonathan McDowell wrote:
> On Wed, Apr 02, 2025 at 07:21:30PM +0200, Michal Suchanek wrote:
> > With some Infineon chips the timeouts in tpm_tis_send_data (both B and
> > C) can reach up to about 2250 ms.
> > 
> > Extend the timeout duration to accommodate this.
> 
> The problem here is the bump of timeout_c is going to interact poorly with
> the Infineon errata workaround, as now we'll wait 4s instead of 200ms to
> detect the stuck status change.

Yes, that's problematic. Is it possible to detect the errata by anything
other than waiting for the timeout to expire?

> 
> (Also shouldn't timeout_c already end up as 750ms, as it's
> max(TIS_SHORT_TIMEOUT, TPM2_TIMEOUT_C), and TIS_SHORT_TIMEOUT is 750 vs 200
> for TPM2_TIMEOUT_C? That doesn't seem to be borne out by your logs, nor my
> results.)

Indeed, it should be 750ms but the logs show 200ms. I do not see
where it could get reduced, nor any significan difference between the
mainline code and the kernel I am using in this area.

Thanks

Michal

> 
> > Link: https://lore.kernel.org/linux-integrity/Z5pI07m0Muapyu9w@kitsune.suse.cz/
> > Signed-off-by: Michal Suchanek <msuchanek@...e.de>
> > ---
> > An alternative would be to add an entry to vendor_timeout_overrides but
> > I do not know how to determine the chip IDs to put into this table.
> > ---
> > drivers/char/tpm/tpm_tis_core.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> > index 970d02c337c7..1ff565be2175 100644
> > --- a/drivers/char/tpm/tpm_tis_core.h
> > +++ b/drivers/char/tpm/tpm_tis_core.h
> > @@ -54,7 +54,7 @@ enum tis_int_flags {
> > enum tis_defaults {
> > 	TIS_MEM_LEN = 0x5000,
> > 	TIS_SHORT_TIMEOUT = 750,	/* ms */
> > -	TIS_LONG_TIMEOUT = 2000,	/* 2 sec */
> > +	TIS_LONG_TIMEOUT = 4000,	/* 2 sec */
> > 	TIS_TIMEOUT_MIN_ATML = 14700,	/* usecs */
> > 	TIS_TIMEOUT_MAX_ATML = 15000,	/* usecs */
> > };
> > @@ -64,7 +64,7 @@ enum tis_defaults {
> >  */
> > #define TIS_TIMEOUT_A_MAX	max_t(int, TIS_SHORT_TIMEOUT, TPM2_TIMEOUT_A)
> > #define TIS_TIMEOUT_B_MAX	max_t(int, TIS_LONG_TIMEOUT, TPM2_TIMEOUT_B)
> > -#define TIS_TIMEOUT_C_MAX	max_t(int, TIS_SHORT_TIMEOUT, TPM2_TIMEOUT_C)
> > +#define TIS_TIMEOUT_C_MAX	max_t(int, TIS_LONG_TIMEOUT, TPM2_TIMEOUT_C)
> > #define TIS_TIMEOUT_D_MAX	max_t(int, TIS_SHORT_TIMEOUT, TPM2_TIMEOUT_D)
> > 
> > #define	TPM_ACCESS(l)			(0x0000 | ((l) << 12))
> > -- 
> > 2.47.1
> > 
> 
> J.
> 
> -- 
> ... "Tom's root boot is the Linux world equivalent of a 'get out of jail
>     free' card. The man is a *hero*." -- Simon Brooke, ucol.