linux-kernel - Re: [PATCH v2 2/4] tpm: support devices with synchronous send()

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Message-ID: <uhqvn5w5ziuzvp3u72kztkfbtkrb2g6ieejup4e2ufun4ywtko@4hcytxdrfues>
Date: Wed, 9 Apr 2025 09:59:26 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>, 
	Nicolas Ferre <nicolas.ferre@...rochip.com>, linux-kernel@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea@...on.dev>, linux-arm-kernel@...ts.infradead.org, 
	Jens Wiklander <jens.wiklander@...aro.org>, linuxppc-dev@...ts.ozlabs.org, 
	Michael Ellerman <mpe@...erman.id.au>, Sumit Garg <sumit.garg@...nel.org>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, linux-integrity@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Naveen N Rao <naveen@...nel.org>, 
	Nicholas Piggin <npiggin@...il.com>, Peter Huewe <peterhuewe@....de>, 
	James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [PATCH v2 2/4] tpm: support devices with synchronous send()

On Tue, Apr 08, 2025 at 06:31:30PM +0300, Jarkko Sakkinen wrote:
>On Tue, Apr 08, 2025 at 10:32:06AM +0200, Stefano Garzarella wrote:
>> From: Stefano Garzarella <sgarzare@...hat.com>
>>
>> Some devices do not support interrupts and provide a single synchronous
>> operation to send the command and receive the response on the same buffer.
>>
>> Currently, these types of drivers must use an internal buffer where they
>> temporarily store the response between .send() and recv() calls.
>>
>> Introduce a new flag (TPM_CHIP_FLAG_SYNC) to support synchronous send().
>> If that flag is set by the driver, tpm_try_transmit() will use the send()
>> callback to send the command and receive the response on the same buffer
>> synchronously. In that case send() return the number of bytes of the
>> response on success, or -errno on failure.
>>
>> Suggested-by: Jason Gunthorpe <jgg@...pe.ca>
>> Suggested-by: Jarkko Sakkinen <jarkko@...nel.org>
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>  include/linux/tpm.h              |  1 +
>>  drivers/char/tpm/tpm-interface.c | 18 +++++++++++++++---
>>  2 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>> index 2e38edd5838c..0e9746dc9d30 100644
>> --- a/include/linux/tpm.h
>> +++ b/include/linux/tpm.h
>> @@ -350,6 +350,7 @@ enum tpm_chip_flags {
>>  	TPM_CHIP_FLAG_SUSPENDED			= BIT(8),
>>  	TPM_CHIP_FLAG_HWRNG_DISABLED		= BIT(9),
>>  	TPM_CHIP_FLAG_DISABLE			= BIT(10),
>> +	TPM_CHIP_FLAG_SYNC			= BIT(11),
>>  };
>>
>>  #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index 3b6ddcdb4051..9fbe84b5a131 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -114,8 +114,17 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>>  		return rc;
>>  	}
>>
>> -	/* A sanity check. send() should just return zero on success e.g.
>> -	 * not the command length.
>> +	/* Synchronous devices return the response directly during the send()
>> +	 * call in the same buffer.
>> +	 */
>
>Nit:
>
>/*
> * ...
>
>It's wrong in the existing comment.

Yep, I'll fix.

>
>> +	if (chip->flags & TPM_CHIP_FLAG_SYNC) {
>> +		len = rc;
>> +		rc = 0;
>> +		goto out_send_sync;
>> +	}
>> +
>> +	/* A sanity check. send() of asynchronous devices should just return

And I'll fix also this of course.

>> +	 * zero on success e.g. not the command length.
>>  	 */
>>  	if (rc > 0) {
>>  		dev_warn(&chip->dev,
>> @@ -151,7 +160,10 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>>  	if (len < 0) {
>>  		rc = len;
>>  		dev_err(&chip->dev, "tpm_transmit: tpm_recv: error %d\n", rc);
>> -	} else if (len < TPM_HEADER_SIZE || len != be32_to_cpu(header->length))
>> +		return rc;
>> +	}
>> +out_send_sync:
>
>out_sync would be sufficient

sure, I'll fix in v3.

Thanks,
Stefano