Re: [PATCH v6 1/3] tpm/tpm_tis_spi: Support TPM for SPI (Serial Peripheral Interface)

[Stefan Berger <stefanb@linux.ibm.com>]

On 11/4/24 12:18 PM, dan tan wrote:
> Implement support for TPM via SPI interface. The SPI bus master
> is provided by PowerNV SPI device which is an SSI peripheral.
> It can uses the tpm_emulator driver backend with the external
> swtpm.
> 
> Signed-off-by: dan tan <dantan@linux.ibm.com>
> ---
> 

> diff --git a/hw/tpm/tpm_tis_spi.c b/hw/tpm/tpm_tis_spi.c
> new file mode 100644
> index 0000000000..079972de03
> --- /dev/null
> +++ b/hw/tpm/tpm_tis_spi.c
> @@ -0,0 +1,357 @@
> +/*
> + * QEMU SPI TPM 2.0 model
> + *
> + * Copyright (c) 2024, IBM Corporation.
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/log.h"
> +#include "hw/sysbus.h"
> +#include "hw/acpi/tpm.h"
> +#include "tpm_prop.h"
> +#include "qemu/log.h"
> +#include "trace.h"
> +#include "tpm_tis.h"
> +#include "hw/ssi/ssi.h"
> +#include "migration/vmstate.h"
> +
> +typedef struct TPMStateSPI {
> +    /*< private >*/
> +    SSIPeripheral parent_object;
> +
> +    uint8_t     byte_offset;     /* byte offset in transfer */
> +    uint8_t     wait_state_cnt;  /* wait state counter */

#define NUM_WAIT_STATES 1

Are 4 wait states actually needed? I ran the test with 1. More wait 
states just have impact on performance and I don't think we need to be 
emulating the real hardware entirely.

@@ -236,9 +237,9 @@ static uint32_t tpm_tis_spi_transfer(SSIPeripheral 
*ss, uint32_t tx)
              trace_tpm_tis_spi_transfer_addr("reg_addr", spist->reg_addr);
              break;
          default:    /* data bytes */
-            if (spist->wait_state_cnt < 4) {
+            if (spist->wait_state_cnt < NUM_WAIT_STATES) {
                  spist->wait_state_cnt++;
-                if (spist->wait_state_cnt == 4) {
+                if (spist->wait_state_cnt == NUM_WAIT_STATES) {
                      trace_tpm_tis_spi_transfer_data("wait complete, 
count",
  
spist->wait_state_cnt);
                      rx = rx | (0x01 << (24 - offset * 8));
@@ -274,7 +275,8 @@ static uint32_t tpm_tis_spi_transfer(SSIPeripheral 
*ss, uint32_t tx)
              }
              break;
          }
-        if ((spist->wait_state_cnt == 0) || (spist->wait_state_cnt == 4)) {
+        if ((spist->wait_state_cnt == 0) ||
+            (spist->wait_state_cnt == NUM_WAIT_STATES)) {
              offset++;
              spist->byte_offset++;
          } else {