Re: [PATCH] Fix Atmel TPM crash caused by too frequent queries

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Sun, 2020-09-27 at 22:59 -0700, Hao Wu wrote:
[...]
> > However, there is another possibility: it's something to do with
> > the byte read; I notice you don't require the same slowdown for the
> > burst count read, which actually reads the status register and
> > burst count as a read32.  If that really is the case, for the atmel
> > would substituting a read32 and just throwing the upper bytes away
> > in tpm_tis_status() allow us to keep the current timings?  I can
> > actually try doing this and see if it fixes my nuvoton.
> 
> If would be helpful if you can find the solution without reducing
> performance. I think it is a separate problem to address though.
> Maybe not worth to mix them in the same fix.

Well, if it works, no other fix is needed.

This is what I'm currently trying out on my nuvoton with the timings
reverted to being those in the vanilla kernel.  So far it hasn't
crashed, but I haven't run it for long enough to be sure yet.

James

---

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 6b884badabe7..c4dbac8edc9b 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -233,9 +233,9 @@ static u8 tpm_tis_status(struct tpm_chip *chip)
 {
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 	int rc;
-	u8 status;
+	u32 status;
 
-	rc = tpm_tis_read8(priv, TPM_STS(priv->locality), &status);
+	rc = tpm_tis_read32(priv, TPM_STS(priv->locality), &status);
 	if (rc < 0)
 		return 0;