Re: [PATCH 2/3] Add support for TPM devices over I2C bus

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

On 3/21/23 01:30, Ninad Palsule wrote:
> Qemu already supports devices attached to ISA and sysbus. This drop adds
> support for the I2C bus attached TPM devices.

> @@ -447,6 +452,15 @@ static uint64_t tpm_tis_mmio_read(void *opaque, hwaddr addr,
>       return val;
>   }
>   
> +/*
> + * A wrapper read function so that it can be directly called without
> + * mmio.
> + */
> +uint32_t tpm_tis_read_data(TPMState *s, hwaddr addr, unsigned size)
> +{
> +    return tpm_tis_mmio_read(s, addr, size);
> +}
> +
>   /*
>    * Write a value to a register of the TIS interface
>    * See specs pages 33-63 for description of the registers
> @@ -600,6 +614,15 @@ static void tpm_tis_mmio_write(void *opaque, hwaddr addr,
>       case TPM_TIS_REG_INT_VECTOR:
>           /* hard wired -- ignore */
>           break;
> +    case TPM_TIS_REG_DATA_CSUM_ENABLE:
> +        /*
> +         * Checksum implemented by common code so no need to set
> +         * any flags.
> +         */

Can you intercept handling this register on the I2C layer and add a byte for its value so that it can be set correctly? We do want to be able to write bit 0 to it to enable it and allow reading of bit 0 to see what the state is. I don't want this byte of state on the TIS layer since this creates state incompatibilities.

And for getting the checksum value it should be also handled on the I2C layer and ask tpm_tis_common.c to run crc_ccitt(0, s->buffer, s->rw_offset) via a function call.

    Stefan