linux-kernel - Re: [PATCH v2 3/4] tpm_tis: Use responseRetry to recover from data transfer errors

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Message-Id: <CT7BN97ICGN7.37I0H14NKKMYR@suppilovahvero>
Date:   Thu, 08 Jun 2023 17:00:15 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Alexander Steffen" <Alexander.Steffen@...ineon.com>,
        <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] tpm_tis: Use responseRetry to recover from data
 transfer errors

On Wed Jun 7, 2023 at 8:14 PM EEST, Alexander Steffen wrote:
> >> -     if (status & TPM_STS_DATA_AVAIL) {      /* retry? */
> >> +     if (status & TPM_STS_DATA_AVAIL) {
> > 
> > Please remove (no-op).
>
> You mean I shouldn't change the line and leave the comment in? To me it 
> looked like a very brief TODO comment "should we retry here?", and since 
> with this change it now actually does retry, I removed it.

Right, ok, point taken, you can keep it.

> >>                dev_err(&chip->dev, "Error left over data\n");
> >>                size = -EIO;
> >>                goto out;
> >> @@ -396,10 +391,39 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> >>        }
> >>
> >>   out:
> >> -     tpm_tis_ready(chip);
> >>        return size;
> >>   }
> >>
> >> +static int tpm_tis_recv_with_retries(struct tpm_chip *chip, u8 *buf, size_t count)
> > 
> > This *substitutes* the curent tpm_tis_recv(), right?
> > 
> > So it *is* tpm_tis_recv(), i.e. no renames thank you :-)
> > 
> >> +{
> >> +     struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >> +     unsigned int try;
> >> +     int rc = 0;
> >> +
> >> +     if (count < TPM_HEADER_SIZE) {
> >> +             rc = -EIO;
> >> +             goto out;
> >> +     }
> >> +
> >> +     for (try = 0; try < TPM_RETRY; try++) {
> >> +             rc = tpm_tis_recv(chip, buf, count);
> > 
> > I would rename single shot tpm_tis_recv() as tpm_tis_try_recv().
> > 
> >> +
> >> +             if (rc == -EIO) {
> >> +                     /* Data transfer errors, indicated by EIO, can be
> >> +                      * recovered by rereading the response.
> >> +                      */
> >> +                     tpm_tis_write8(priv, TPM_STS(priv->locality),
> >> +                                    TPM_STS_RESPONSE_RETRY);
> >> +             } else {
> >> +                     break;
> >> +             }
> > 
> > And if this should really be managed inside tpm_tis_try_recv(), and
> > then return zero (as the code block consumes the return value).
>
> What exactly should be done in tpm_tis_try_recv()? It could set 
> TPM_STS_RESPONSE_RETRY, but then it would still need to return an error 
> code, so that this loop knows whether to call it again or not.

So my thinking was to:

- Rename tpm_tis_recv() as tpm_tis_try_recv()
- Rename this new function as tpm_tis_recv().

BR, Jarkko