linux-kernel - [PATCH v4 4/4] tpm/tpm_svsm: support TPM_CHIP_FLAG

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Message-ID: <20250509085713.76851-5-sgarzare@redhat.com>
Date: Fri,  9 May 2025 10:57:13 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org,
	Peter Huewe <peterhuewe@....de>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Naveen N Rao <naveen@...nel.org>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	linux-integrity@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Nicholas Piggin <npiggin@...il.com>,
	Sumit Garg <sumit.garg@...nel.org>,
	Stefano Garzarella <sgarzare@...hat.com>
Subject: [PATCH v4 4/4] tpm/tpm_svsm: support TPM_CHIP_FLAG_SYNC

From: Stefano Garzarella <sgarzare@...hat.com>

This driver does not support interrupts, and receiving the response is
synchronous with sending the command.

Enable synchronous send() with TPM_CHIP_FLAG_SYNC, which implies that
->send() already fills the provided buffer with a response, and ->recv()
is not implemented.

Keep using the same pre-allocated buffer to avoid having to allocate
it for each command. We need the buffer to have the header required by
the SVSM protocol and the command contiguous in memory.

Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---
v4:
- reworked commit description [Jarkko]
---
 drivers/char/tpm/tpm_svsm.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/char/tpm/tpm_svsm.c b/drivers/char/tpm/tpm_svsm.c
index d3ca5615b6f7..db1983072345 100644
--- a/drivers/char/tpm/tpm_svsm.c
+++ b/drivers/char/tpm/tpm_svsm.c
@@ -25,38 +25,32 @@ struct tpm_svsm_priv {
 	void *buffer;
 };
 
-static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t len,
+static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t cmd_len,
 			 size_t buf_size)
 {
 	struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
 	int ret;
 
-	ret = svsm_vtpm_cmd_request_fill(priv->buffer, 0, buf, len);
+	ret = svsm_vtpm_cmd_request_fill(priv->buffer, 0, buf, cmd_len);
 	if (ret)
 		return ret;
 
 	/*
 	 * The SVSM call uses the same buffer for the command and for the
-	 * response, so after this call, the buffer will contain the response
-	 * that can be used by .recv() op.
+	 * response, so after this call, the buffer will contain the response.
+	 *
+	 * Note: we have to use an internal buffer because the device in SVSM
+	 * expects the svsm_vtpm header + data to be physically contiguous.
 	 */
-	return snp_svsm_vtpm_send_command(priv->buffer);
-}
-
-static int tpm_svsm_recv(struct tpm_chip *chip, u8 *buf, size_t len)
-{
-	struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
+	ret = snp_svsm_vtpm_send_command(priv->buffer);
+	if (ret)
+		return ret;
 
-	/*
-	 * The internal buffer contains the response after we send the command
-	 * to SVSM.
-	 */
-	return svsm_vtpm_cmd_response_parse(priv->buffer, buf, len);
+	return svsm_vtpm_cmd_response_parse(priv->buffer, buf, buf_size);
 }
 
 static struct tpm_class_ops tpm_chip_ops = {
 	.flags = TPM_OPS_AUTO_STARTUP,
-	.recv = tpm_svsm_recv,
 	.send = tpm_svsm_send,
 };
 
@@ -85,6 +79,7 @@ static int __init tpm_svsm_probe(struct platform_device *pdev)
 
 	dev_set_drvdata(&chip->dev, priv);
 
+	chip->flags |= TPM_CHIP_FLAG_SYNC;
 	err = tpm2_probe(chip);
 	if (err)
 		return err;
-- 
2.49.0