tpm/tpm_svsm: support TPM_CHIP_FLAG_SYNC

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@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

drivers/char/tpm/tpm_svsm.c

@@ -26,37 +26,31 @@ struct tpm_svsm_priv {
 };
 
 static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz,
-			 size_t len)
+			 size_t cmd_len)
 {
 	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);
-}
+	ret = snp_svsm_vtpm_send_command(priv->buffer);
+	if (ret)
+		return ret;
 
-static int tpm_svsm_recv(struct tpm_chip *chip, u8 *buf, size_t len)
-{
-	struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
-
-	/*
-	 * 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, bufsiz);
 }
 
 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;