On Wed, Mar 05, 2025 at 09:45:15AM +0000, Jonathan McDowell wrote:
> From: Jonathan McDowell <nood...@meta.com>
>
> The change to only use interrupts to handle supported status changes,
> then switch to polling for the rest, inverted the status test and sleep
> such that we can end up sleeping beyond our timeout and not actually
> checking the status. This can result in spurious TPM timeouts,
I *really* have hard time understanding what I'm reading the first
sentence *but* I do understand the code change. Maybe you could try
to be a bit more punctual there...
> especially on a more loaded system. Fix by switching the order back so
> we sleep *then* check. We've done a up front check when we enter the
> function so this won't cause an additional delay when the status is
> already what we're looking for.
Remove the use of we-pronoun: it is best for science papers. Also, e.g.
why not just say "switch" instead of "fix by switching" ? :-)
I'd rewrite this tail part like:
"Switch the order back where it was i.e., sleep before check."
Instead of "upfront check" it'd nice to be a bit more specific...
>
> Cc: sta...@vger.kernel.org # v6.4+
> Fixes: e87fcf0dc2b4 ("tpm, tpm_tis: Only handle supported interrupts")
> Signed-off-by: Jonathan McDowell <nood...@meta.com>
> Reviewed-by: Michal Suchánek <msucha...@suse.de>
> ---
> drivers/char/tpm/tpm_tis_core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index fdef214b9f6b..167d71747666 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -114,11 +114,11 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8
> mask,
> return 0;
> /* process status changes without irq support */
> do {
> + usleep_range(priv->timeout_min,
> + priv->timeout_max);
> status = chip->ops->status(chip);
> if ((status & mask) == mask)
> return 0;
> - usleep_range(priv->timeout_min,
> - priv->timeout_max);
> } while (time_before(jiffies, stop));
> return -ETIME;
> }
> --
> 2.48.1
>
>
The fix itself looks legit although you could just as well put it into a
single line.
BR, Jarkko
