Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class_ops

Stefano Garzarella
2025-03-03T17:29:28Z

On Mon, Mar 03, 2025 at 08:06:43AM -0600, Tom Lendacky wrote:
>On 2/28/25 11:07, Stefano Garzarella wrote:
>> Some devices do not support interrupts and provide a single operation
>> to send the command and receive the response on the same buffer.
>>
>> To support this scenario, a driver could set TPM_CHIP_FLAG_IRQ in the
>> chip's flags to get recv() to be called immediately after send() in
>> tpm_try_transmit().
>>
>> Instead of abusing TPM_CHIP_FLAG_IRQ, introduce a new callback
>> send_recv(). If that callback is defined, it is called in
>> tpm_try_transmit() to send the command and receive the response on
>> the same buffer in a single call.
>>
>> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>> include/linux/tpm.h | 2 ++
>> drivers/char/tpm/tpm-interface.c | 8 +++++++-
>> 2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>> index 20a40ade8030..2ede8e0592d3 100644
>> --- a/include/linux/tpm.h
>> +++ b/include/linux/tpm.h
>> @@ -88,6 +88,8 @@ struct tpm_class_ops {
>> bool (*req_canceled)(struct tpm_chip *chip, u8 status);
>> int (*recv) (struct tpm_chip *chip, u8 *buf, size_t len);
>> int (*send) (struct tpm_chip *chip, u8 *buf, size_t len);
>> + int (*send_recv)(struct tpm_chip *chip, u8 *buf, size_t buf_len,
>> + size_t to_send);
>> void (*cancel) (struct tpm_chip *chip);
>> u8 (*status) (struct tpm_chip *chip);
>> void (*update_timeouts)(struct tpm_chip *chip,
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index b1daa0d7b341..4f92b0477696 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -82,6 +82,9 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>> return -E2BIG;
>> }
>>
>> + if (chip->ops->send_recv)
>> + goto out_recv;
>
>It might look a bit cleaner if you issue the send_recv() call here and
>then jump to a new label after the recv() call just before 'len' is checked.

Yep, I see, I was undecided to avoid adding a new label and just have
out_recv which in future cases always handles the send_recv() case.
But maybe I overthought, I will do as you suggest.

Thanks,
Stefano

>
>Thanks,
>Tom
>
>> +
>> rc = chip->ops->send(chip, buf, count);
>> if (rc < 0) {
>> if (rc != -EPIPE)
>> @@ -123,7 +126,10 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>> return -ETIME;
>>
>> out_recv:
>> - len = chip->ops->recv(chip, buf, bufsiz);
>> + if (chip->ops->send_recv)
>> + len = chip->ops->send_recv(chip, buf, bufsiz, count);
>> + else
>> + len = chip->ops->recv(chip, buf, bufsiz);
>> if (len < 0) {
>> rc = len;
>> dev_err(&chip->dev, "tpm_transmit: tpm_recv: error %d\n", rc);
>