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

[Alexander Steffen <Alexander.Steffen@infineon.com>]

On 08.06.23 16:00, Jarkko Sakkinen wrote:
> 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().

Sounds good, thanks. Will be done in v3.

> BR, Jarkko