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

[Ninad Palsule <ninad@linux.vnet.ibm.com>]

On 3/23/23 3:37 AM, Cédric Le Goater wrote:
> On 3/23/23 04:01, Ninad Palsule wrote:
>> Qemu already supports devices attached to ISA and sysbus. This drop adds
>> support for the I2C bus attached TPM devices. I2C model only supports
>> TPM2 protocol.
>>
>> This commit includes changes for the common code.
>> - Added I2C emulation model. Logic was added in the model to temporarily
>>    cache the data as I2C interface works per byte basis.
>> - New tpm type "tpm-tis-i2c" added for I2C support. User specify this
>>    string on command line.
>>
>> Testing:
>>    TPM I2C device modulte is tested using SWTPM (software based TPM
>>    package). The qemu used the rainier machine and it was connected to
>>    swtpm over the socket interface.
>>
>>    The command to start swtpm is as follows:
>>    $ swtpm socket --tpmstate dir=/tmp/mytpm1    \
>>                   --ctrl type=unixio,path=/tmp/mytpm1/swtpm-sock  \
>>                   --tpm2 --log level=100
>>
>>    The command to start qemu is as follows:
>>    $ qemu-system-arm -M rainier-bmc -nographic \
>>              -kernel ${IMAGEPATH}/fitImage-linux.bin \
>>              -dtb ${IMAGEPATH}/aspeed-bmc-ibm-rainier.dtb \
>>              -initrd 
>> ${IMAGEPATH}/obmc-phosphor-initramfs.rootfs.cpio.xz \
>>              -drive 
>> file=${IMAGEPATH}/obmc-phosphor-image.rootfs.wic.qcow2,if=sd,index=2 \
>>              -net nic -net 
>> user,hostfwd=:127.0.0.1:2222-:22,hostfwd=:127.0.0.1:2443-:443 \
>>              -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \
>>              -tpmdev emulator,id=tpm0,chardev=chrtpm \
>>              -device 
>> tpm-tis-i2c,tpmdev=tpm0,bus=aspeed.i2c.bus.12,address=0x2e
>>
>>    Note: Currently you need to specify the I2C bus and device address on
>>          command line. In future we can add a device at board level.
>
> yes. Anyhow, it is better to start with user created device first than 
> with
> default devices created at the board level.


I could not find the  arch/arm/boot/dts/aspeed-ast2600-evb.dtb in 
https://jenkins.openbmc.org/job/ci-openbmc/lastSuccessfulBuild/ 
<https://jenkins.openbmc.org/job/ci-openbmc/lastSuccessfulBuild/>. Can 
you please point me to the location?

>
>>
>> Signed-off-by: Ninad Palsule <ninad@linux.ibm.com>
>> ---
>> V2:
>> Incorporated Stephen's review comments.
>> - Handled checksum related register in I2C layer
>> - Defined I2C interface capabilities and return those instead of
>>    capabilities from TPM TIS. Add required capabilities from TIS.
>> - Do not cache FIFO data in the I2C layer.
>> - Make sure that Device address change register is not passed to I2C
>>    layer as capability indicate that it is not supported.
>> - Added boundary checks.
>> - Make sure that bits 26-31 are zeroed for the TPM_STS register on read
>> - Updated Kconfig files for new define.
>> ---
>>   hw/arm/Kconfig       |   1 +
>>   hw/tpm/Kconfig       |   7 +
>>   hw/tpm/meson.build   |   1 +
>>   hw/tpm/tpm_tis_i2c.c | 440 +++++++++++++++++++++++++++++++++++++++++++
>>   include/sysemu/tpm.h |   3 +
>>   5 files changed, 452 insertions(+)
>>   create mode 100644 hw/tpm/tpm_tis_i2c.c
>>
>> diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
>> index b5aed4aff5..05d6ef1a31 100644
>> --- a/hw/arm/Kconfig
>> +++ b/hw/arm/Kconfig
>> @@ -6,6 +6,7 @@ config ARM_VIRT
>>       imply VFIO_PLATFORM
>>       imply VFIO_XGMAC
>>       imply TPM_TIS_SYSBUS
>> +    imply TPM_TIS_I2C
>>       imply NVDIMM
>>       select ARM_GIC
>>       select ACPI
>> diff --git a/hw/tpm/Kconfig b/hw/tpm/Kconfig
>> index 29e82f3c92..a46663288c 100644
>> --- a/hw/tpm/Kconfig
>> +++ b/hw/tpm/Kconfig
>> @@ -1,3 +1,10 @@
>> +config TPM_TIS_I2C
>> +    bool
>> +    depends on TPM
>> +    select TPM_BACKEND
>> +    select I2C
>> +    select TPM_TIS
>> +
>>   config TPM_TIS_ISA
>>       bool
>>       depends on TPM && ISA_BUS
>> diff --git a/hw/tpm/meson.build b/hw/tpm/meson.build
>> index 7abc2d794a..76fe3cb098 100644
>> --- a/hw/tpm/meson.build
>> +++ b/hw/tpm/meson.build
>> @@ -1,6 +1,7 @@
>>   softmmu_ss.add(when: 'CONFIG_TPM_TIS', if_true: 
>> files('tpm_tis_common.c'))
>>   softmmu_ss.add(when: 'CONFIG_TPM_TIS_ISA', if_true: 
>> files('tpm_tis_isa.c'))
>>   softmmu_ss.add(when: 'CONFIG_TPM_TIS_SYSBUS', if_true: 
>> files('tpm_tis_sysbus.c'))
>> +softmmu_ss.add(when: 'CONFIG_TPM_TIS_I2C', if_true: 
>> files('tpm_tis_i2c.c'))
>>   softmmu_ss.add(when: 'CONFIG_TPM_CRB', if_true: files('tpm_crb.c'))
>>   softmmu_ss.add(when: 'CONFIG_TPM_TIS', if_true: files('tpm_ppi.c'))
>>   softmmu_ss.add(when: 'CONFIG_TPM_CRB', if_true: files('tpm_ppi.c'))
>> diff --git a/hw/tpm/tpm_tis_i2c.c b/hw/tpm/tpm_tis_i2c.c
>> new file mode 100644
>> index 0000000000..5cec5f7806
>> --- /dev/null
>> +++ b/hw/tpm/tpm_tis_i2c.c
>> @@ -0,0 +1,440 @@
>> +/*
>> + * tpm_tis_i2c.c - QEMU's TPM TIS I2C Device
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 
>> or later.
>> + * See the COPYING file in the top-level directory.
>> + *
>> + * Implementation of the TIS interface according to specs found at
>> + * http://www.trustedcomputinggroup.org. This implementation currently
>> + * supports version 1.3, 21 March 2013
>> + * In the developers menu choose the PC Client section then find the 
>> TIS
>> + * specification.
>> + *
>> + * TPM TIS for TPM 2 implementation following TCG PC Client Platform
>> + * TPM Profile (PTP) Specification, Familiy 2.0, Revision 00.43
>> + *
>> + * TPM I2C implementation follows TCG TPM I2c Interface specification,
>> + * Family 2.0, Level 00, Revision 1.00
>> + */
>> +
>> +#include "qemu/osdep.h"
>> +#include "hw/i2c/i2c.h"
>> +#include "hw/qdev-properties.h"
>> +#include "hw/acpi/tpm.h"
>> +#include "migration/vmstate.h"
>> +#include "tpm_prop.h"
>> +#include "tpm_tis.h"
>> +#include "qom/object.h"
>> +#include "block/aio.h"
>> +#include "qemu/main-loop.h"
>> +
>> +/* TPM TIS I2C registers */
>> +#define TPM_TIS_I2C_REG_LOC_SEL          0x00
>> +#define TPM_TIS_I2C_REG_ACCESS           0x04
>> +#define TPM_TIS_I2C_REG_INT_ENABLE       0x08
>> +#define TPM_TIS_I2C_REG_INT_CAPABILITY   0x14
>> +#define TPM_TIS_I2C_REG_STS              0x18
>> +#define TPM_TIS_I2C_REG_DATA_FIFO        0x24
>> +#define TPM_TIS_I2C_REG_INTF_CAPABILITY  0x30
>> +#define TPM_TIS_I2C_REG_I2C_DEV_ADDRESS  0x38
>> +#define TPM_TIS_I2C_REG_DATA_CSUM_ENABLE 0x40
>> +#define TPM_TIS_I2C_REG_DATA_CSUM_GET    0x44
>> +#define TPM_TIS_I2C_REG_DID_VID          0x48
>> +#define TPM_TIS_I2C_REG_RID              0x4c
>> +#define TPM_TIS_I2C_REG_UNKNOWN          0xff
>> +
>> +/* I2C specific interface capabilities */
>> +#define TPM_I2C_CAP_INTERFACE_TYPE     (0x2 << 0) /* FIFO interface */
>> +#define TPM_I2C_CAP_INTERFACE_VER      (0x0 << 4) /* TCG I2C intf 
>> 1.0 */
>> +#define TPM_I2C_CAP_TPM2_FAMILY        (0x1 << 7) /* TPM 2.0 family. */
>> +#define TPM_I2C_CAP_DEV_ADDR_CHANGE    (0x0 << 27) /* No dev addr 
>> chng */
>> +#define TPM_I2C_CAP_BURST_COUNT_STATIC (0x1 << 29) /* Burst count 
>> static */
>> +#define TPM_I2C_CAP_LOCALITY_CAP       (0x1 << 25) /* 0-5 locality */
>> +#define TPM_I2C_CAP_BUS_SPEED          (3   << 21) /* std and fast 
>> mode */
>> +
>> +/* TPM_STS mask for read bits 31:26 must be zero */
>> +#define TPM_I2C_STS_READ_MASK          0x03ffffff
>> +
>> +/* Operations */
>> +#define OP_SEND   1
>> +#define OP_RECV   2
>> +
>> +typedef struct TPMStateI2C {
>> +    /*< private >*/
>> +    I2CSlave parent_obj;
>> +
>> +    int      offset;     /* offset in to data[] */
>> +    int      size;       /* Size of the current reg data */
>> +    uint8_t  operation;  /* OP_SEND & OP_RECV */
>> +    uint8_t  data[4096]; /* Data */
>
> That's a lot of bytes. What is the max in HW ?
I was initially caching whole page now I change the login on write so I 
change the value to 16.
>
>> +
>> +    bool     csum_enable;
>> +    uint32_t tis_intf_cap;  /* save TIS interface Capabilities */
>> +
>> +    /*< public >*/
>> +    TPMState state; /* not a QOM object */
>
> hmm, why ? is that per design of the TPM model ?
>
Yes, That is required for the TPM model.


>> +
>> +} TPMStateI2C;
>> +
>> +DECLARE_INSTANCE_CHECKER(TPMStateI2C, TPM_TIS_I2C,
>> +                         TYPE_TPM_TIS_I2C)
>> +
>> +/* Register map */
>> +typedef struct reg_map {
>> +    uint16_t  i2c_reg;    /* I2C register */
>> +    uint16_t  tis_reg;    /* TIS register */
>> +    uint32_t  data_size;  /* data size expected */
>> +} i2c_reg_map;
>
> QEMU prefers CamelCase coding style for types.


I changed reg_map to CamelCase.

>
>> +
>> +/*
>> + * The register values in the common code is different than the latest
>> + * register numbers as per the spec hence add the conversion map
>> + */
>> +static const i2c_reg_map tpm_tis_reg_map[] = {
>> +    { TPM_TIS_I2C_REG_LOC_SEL, TPM_TIS_REG_ACCESS,               1, },
>> +    { TPM_TIS_I2C_REG_ACCESS, TPM_TIS_REG_ACCESS,               1, },
>> +    { TPM_TIS_I2C_REG_INT_ENABLE, TPM_TIS_REG_INT_ENABLE,           
>> 4, },
>> +    { TPM_TIS_I2C_REG_INT_CAPABILITY, 
>> TPM_TIS_REG_INT_VECTOR,           4, },
>> +    { TPM_TIS_I2C_REG_STS, TPM_TIS_REG_STS,                  4, },
>> +    { TPM_TIS_I2C_REG_DATA_FIFO, TPM_TIS_REG_DATA_FIFO,            
>> 0, },
>> +    { TPM_TIS_I2C_REG_INTF_CAPABILITY, 
>> TPM_TIS_REG_INTF_CAPABILITY,      4, },
>> +    { TPM_TIS_I2C_REG_I2C_DEV_ADDRESS, 
>> TPM_TIS_I2C_REG_I2C_DEV_ADDRESS,  2, },
>> +    { TPM_TIS_I2C_REG_DATA_CSUM_ENABLE, 
>> TPM_TIS_I2C_REG_DATA_CSUM_ENABLE, 1, },
>> +    { TPM_TIS_I2C_REG_DATA_CSUM_GET, 
>> TPM_TIS_I2C_REG_DATA_CSUM_GET,    2, },
>> +    { TPM_TIS_I2C_REG_DID_VID, TPM_TIS_REG_DID_VID,              4, },
>> +    { TPM_TIS_I2C_REG_RID, TPM_TIS_REG_RID,                  1, },
>> +};
>> +
>> +/* Generate interface capability based on what is returned by TIS 
>> and what is
>> + * expected by I2C. Save the capability in the data array 
>> overwriting the TIS
>> + * capability.
>> + */
>> +static uint32_t tpm_i2c_interface_capability(TPMStateI2C *i2cst, 
>> uint32_t tis_cap)
>> +{
>> +    uint32_t i2c_cap = 0;
>> +
>> +    i2cst->tis_intf_cap = tis_cap;
>> +
>> +    /* Now generate i2c capability */
>> +    i2c_cap = (TPM_I2C_CAP_INTERFACE_TYPE |
>> +               TPM_I2C_CAP_INTERFACE_VER  |
>> +               TPM_I2C_CAP_TPM2_FAMILY    |
>> +               TPM_I2C_CAP_LOCALITY_CAP   |
>> +               TPM_I2C_CAP_BUS_SPEED      |
>> +               TPM_I2C_CAP_DEV_ADDR_CHANGE);
>> +
>> +    /* Now check the TIS and set some capabilities */
>> +
>> +    /* Static burst count set */
>> +    if (i2cst->tis_intf_cap & 0x100) {
>> +        i2c_cap |= TPM_I2C_CAP_BURST_COUNT_STATIC;
>> +    }
>> +
>> +    return i2c_cap;
>> +}
>> +
>> +static inline uint16_t tpm_tis_i2c_to_tis_reg(uint64_t i2c_reg, int 
>> *size)
>> +{
>> +    uint16_t tis_reg = i2c_reg;
>> +    const i2c_reg_map *reg_map;
>> +    int i;
>> +
>> +    for (i = 0; i < ARRAY_SIZE(tpm_tis_reg_map); i++) {
>> +        reg_map = &tpm_tis_reg_map[i];
>> +        if (reg_map->i2c_reg == (i2c_reg & 0xff)) {
>> +            tis_reg = reg_map->tis_reg;
>> +            *size = reg_map->data_size;
>> +            break;
>> +        }
>> +    }
>> +
>> +    return tis_reg;
>> +}
>> +
>> +/* Initialize the cached data */
>> +static inline void tpm_tis_i2c_init_cache(TPMStateI2C *i2cst)
>> +{
>> +    /* Clear operation and offset */
>> +    i2cst->operation = 0;
>> +    i2cst->offset = 0;
>> +    i2cst->size = 0;
>> +
>> +    return;
>> +}
>> +
>> +/* Send data to TPM */
>> +static inline void tpm_tis_i2c_tpm_send(TPMStateI2C *i2cst)
>> +{
>> +    uint16_t tis_reg;
>> +    uint32_t data;
>> +    int      i;
>> +
>> +    if ((i2cst->operation == OP_SEND) && (i2cst->offset > 1)) {
>> +
>> +        /*
>> +         * Checksum is not handled by common code hence we will 
>> consume the
>> +         * register here.
>> +         */
>> +        if (i2cst->data[0] == TPM_TIS_I2C_REG_DATA_CSUM_ENABLE) {
>> +            i2cst->csum_enable = true;
>> +        } else if (i2cst->data[0] != TPM_TIS_I2C_REG_DATA_FIFO) {
>> +            tis_reg = tpm_tis_i2c_to_tis_reg(i2cst->data[0], 
>> &i2cst->size);
>> +
>> +            /* Index 0 is always a register */
>> +            for (i = 1; i < i2cst->offset; i++) {
>> +                data = i2cst->data[i];
>> +                tpm_tis_write_data(&i2cst->state, tis_reg, data, 1);
>> +            }
>> +        }
>> +
>> +        tpm_tis_i2c_init_cache(i2cst);
>> +    }
>> +
>> +    return;
>> +}
>> +
>> +/* Callback from TPM to indicate that response is copied */
>> +static void tpm_tis_i2c_request_completed(TPMIf *ti, int ret)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(ti);
>> +    TPMState *s = &i2cst->state;
>> +
>> +    /* Inform the common code. */
>> +    tpm_tis_request_completed(s, ret);
>> +}
>> +
>> +static enum TPMVersion tpm_tis_i2c_get_tpm_version(TPMIf *ti)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(ti);
>> +    TPMState *s = &i2cst->state;
>> +
>> +    return tpm_tis_get_tpm_version(s);
>> +}
>> +
>> +static int tpm_tis_i2c_event(I2CSlave *i2c, enum i2c_event event)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
>> +    int ret = 0;
>> +
>> +    switch (event) {
>> +    case I2C_START_RECV:
>> +        break;
>> +    case I2C_START_SEND:
>> +        tpm_tis_i2c_init_cache(i2cst);
>> +        break;
>> +    case I2C_FINISH:
>> +        if (i2cst->operation == OP_SEND) {
>> +            tpm_tis_i2c_tpm_send(i2cst);
>> +        } else {
>> +            tpm_tis_i2c_init_cache(i2cst);
>> +        }
>> +        break;
>> +    default:
>> +        break;
>> +    }
>> +
>> +    return ret;
>> +}
>> +
>> +/*
>> + * If data is for FIFO then it is received from tpm_tis_common buffer
>> + * otherwise it will be handled using single call to common code and
>> + * cached in the local buffer.
>> + */
>> +static uint8_t tpm_tis_i2c_recv(I2CSlave *i2c)
>> +{
>> +    int ret = 0;
>> +    int i, j;
>> +    uint32_t addr;
>> +    uint32_t data_read;
>> +    uint16_t i2c_reg;
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
>> +    TPMState *s = &i2cst->state;
>> +
>> +    if (i2cst->operation == OP_RECV) {
>> +
>> +        /* Do not cache FIFO data. */
>> +        if (i2cst->data[0] == TPM_TIS_I2C_REG_DATA_FIFO) {
>> +            addr = tpm_tis_i2c_to_tis_reg(TPM_TIS_I2C_REG_DATA_FIFO,
>> +                                          &i2cst->size);
>> +            data_read = tpm_tis_read_data(s, addr, 1);
>> +            ret = (data_read & 0xff);
>> +        } else if (i2cst->offset < 4096) {
>
> use a define or sizeof(i2cst->data)
Done
>
>> +            ret = i2cst->data[i2cst->offset++];
>> +        }
>> +
>> +    } else if ((i2cst->operation == OP_SEND) && (i2cst->offset < 2)) {
>> +        /* First receive call after send */
>> +
>> +        i2c_reg = i2cst->data[0];
>> +
>> +        i2cst->operation = OP_RECV;
>> +        i2cst->offset = 1; /* keep the register value intact for 
>> debug */
>> +
>> +        addr = tpm_tis_i2c_to_tis_reg(i2c_reg, &i2cst->size);
>> +
>> +        /* FIFO data is directly read from TPM TIS */
>> +        if (i2c_reg == TPM_TIS_I2C_REG_DATA_FIFO) {
>> +            data_read = tpm_tis_read_data(s, addr, 1);
>> +            ret = (data_read & 0xff);
>> +        } else {
>> +            /*
>> +             * Save the data in the data field. Save it in the little
>> +             * endian format.
>> +             */
>> +            for (i = 1; i <= i2cst->size;) {
>> +                /*
>> +                 * Checksum registers are not supported by common 
>> code hence
>> +                 * call a common code to get the checksum.
>> +                 */
>> +                if (i2c_reg == TPM_TIS_I2C_REG_DATA_CSUM_GET) {
>> +                    data_read = tpm_tis_get_checksum(s);
>> +                } else {
>> +                    data_read = tpm_tis_read_data(s, addr, 4);
>> +
>> +                    if (i2c_reg == TPM_TIS_I2C_REG_INTF_CAPABILITY) {
>> +                        /* Prepare the capabilities as per I2C 
>> interface */
>> +                        data_read = tpm_i2c_interface_capability(i2cst,
>> + data_read);
>> +                    } else if (i2c_reg == TPM_TIS_I2C_REG_STS) {
>> +                        /*
>> +                         * As per specs, STS bit 31:26 are reserved 
>> and must
>> +                         * be set to 0
>> +                         */
>> +                        data_read &= TPM_I2C_STS_READ_MASK;
>> +                    }
>> +                }
>> +                for (j = 0; j < 4; j++) {
>> +                    i2cst->data[i++] = (data_read & 0xff);
>> +                    data_read >>= 8;
>> +                }
>
> Why do you need 2 loops ? This is complex to follow.
You are right. Now that I moved writes to TIS , I am able to remove 
outer loop.
>
>> +            }
>> +            /* Return first byte with this call */
>> +            ret = i2cst->data[i2cst->offset++];
>> +        }
>> +    } else {
>> +        i2cst->operation = OP_RECV;
>> +    }
>> +
>> +    return ret;
>> +}
>> +
>> +/*
>> + * Send function only remembers data in the buffer and then calls
>> + * TPM TIS common code during FINISH event.
>> + */
>> +static int tpm_tis_i2c_send(I2CSlave *i2c, uint8_t data)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
>> +    uint16_t tis_reg;
>> +
>> +    /* Reject non-supported registers. */
>> +    if (i2cst->offset == 0) {
>> +        /* We do not support device address change */
>> +        if (data == TPM_TIS_I2C_REG_I2C_DEV_ADDRESS) {
>
> may be add a qemu_log_mask(LOG_UNIMP, "  ...");
Done
>
>> +            return 1;
>> +        }
>> +    }
>> +
>> +    if (i2cst->offset < 4096) {
>
> use a define or sizeof(i2cst->data)
Done
>
>> +        i2cst->operation = OP_SEND;
>> +
>> +        /* Remember data locally for non-FIFO registers */
>> +        if ((i2cst->offset == 0) ||
>> +            (i2cst->data[0] != TPM_TIS_I2C_REG_DATA_FIFO)) {
>> +            i2cst->data[i2cst->offset++] = data;
>> +        } else {
>> +            tis_reg = tpm_tis_i2c_to_tis_reg(i2cst->data[0], 
>> &i2cst->size);
>> +            tpm_tis_write_data(&i2cst->state, tis_reg, data, 1);
>> +        }
>> +
>> +        return 0;
>> +
>> +    } else {
>> +        /* Return non-zero to indicate NAK */
>> +        return 1;
>> +    }
>> +}
>> +
>> +static Property tpm_tis_i2c_properties[] = {
>> +    DEFINE_PROP_UINT32("irq", TPMStateI2C, state.irq_num, TPM_TIS_IRQ),
>
> hmm, irq seems unused.
I is used in the TIS and backend.
>
>> +    DEFINE_PROP_TPMBE("tpmdev", TPMStateI2C, state.be_driver),
>> +    DEFINE_PROP_END_OF_LIST(),
>> +};
>
> I don't see an .instance_init routine initializing the TPMState sub 
> device.


The TPMState initialization happens under tpm_tis_reset.


>
>> +
>> +static void tpm_tis_i2c_realizefn(DeviceState *dev, Error **errp)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(dev);
>> +    TPMState *s = &i2cst->state;
>> +
>> +    if (!tpm_find()) {
>> +        error_setg(errp, "at most one TPM device is permitted");
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Get the backend pointer. It is not initialized propery during
>> +     * device_class_set_props
>> +     */
>> +    s->be_driver = qemu_find_tpm_be("tpm0");
>
> I don't understand that part. Looks weird to me.
It should happen under device_class_set_props() but this function is 
getting invoked before tpm0 is created hence I had to query separately 
in the realize function.
>
>> +    if (!s->be_driver) {
>> +        error_setg(errp, "'tpmdev' property is required");
>> +        return;
>> +    }
>> +    if (s->irq_num > 15) {
>> +        error_setg(errp, "IRQ %d is outside valid range of 0 to 15",
>> +                   s->irq_num);
>> +        return;
>> +    }
>
> The code above belongs to a TPMState realize routine it seems. I was
> expecting something like :
>
>     if (!qdev_realize(qdev_realize(DEVICE(&i2cst->state), NULL, &errp)) {
>     return;
>     }
>   Looking closer, this comment applies to some other tpm devices. May be
> I misunderstood how TPM is designed though.
>
I followed direction from tpm_tis_sysbus.c code. But I still had to call 
find backend.

Thanks for the review.

Ninad

> Thanks,
>
> C.
>
>> +}
>> +
>> +static void tpm_tis_i2c_reset(DeviceState *dev)
>> +{
>> +    TPMStateI2C *i2cst = TPM_TIS_I2C(dev);
>> +    TPMState *s = &i2cst->state;
>> +
>> +    tpm_tis_i2c_init_cache(i2cst);
>> +
>> +    i2cst->csum_enable = false;
>> +
>> +    return tpm_tis_reset(s);
>> +}
>> +
>> +static void tpm_tis_i2c_class_init(ObjectClass *klass, void *data)
>> +{
>> +    DeviceClass *dc = DEVICE_CLASS(klass);
>> +    I2CSlaveClass *k = I2C_SLAVE_CLASS(klass);
>> +    TPMIfClass *tc = TPM_IF_CLASS(klass);
>> +
>> +    dc->realize = tpm_tis_i2c_realizefn;
>> +    dc->reset = tpm_tis_i2c_reset;
>> +    device_class_set_props(dc, tpm_tis_i2c_properties);
>> +
>> +    k->event = tpm_tis_i2c_event;
>> +    k->recv = tpm_tis_i2c_recv;
>> +    k->send = tpm_tis_i2c_send;
>> +
>> +    tc->model = TPM_MODEL_TPM_TIS;
>> +    tc->request_completed = tpm_tis_i2c_request_completed;
>> +    tc->get_version = tpm_tis_i2c_get_tpm_version;
>> +}
>> +
>> +static const TypeInfo tpm_tis_i2c_info = {
>> +    .name          = TYPE_TPM_TIS_I2C,
>> +    .parent        = TYPE_I2C_SLAVE,
>> +    .instance_size = sizeof(TPMStateI2C),
>> +    .class_init    = tpm_tis_i2c_class_init,
>> +        .interfaces = (InterfaceInfo[]) {
>> +        { TYPE_TPM_IF },
>> +        { }
>> +    }
>> +};
>> +
>> +static void tpm_tis_i2c_register_types(void)
>> +{
>> +    type_register_static(&tpm_tis_i2c_info);
>> +}
>> +
>> +type_init(tpm_tis_i2c_register_types)
>> diff --git a/include/sysemu/tpm.h b/include/sysemu/tpm.h
>> index fb40e30ff6..66e3b45f30 100644
>> --- a/include/sysemu/tpm.h
>> +++ b/include/sysemu/tpm.h
>> @@ -48,6 +48,7 @@ struct TPMIfClass {
>>   #define TYPE_TPM_TIS_SYSBUS         "tpm-tis-device"
>>   #define TYPE_TPM_CRB                "tpm-crb"
>>   #define TYPE_TPM_SPAPR              "tpm-spapr"
>> +#define TYPE_TPM_TIS_I2C            "tpm-tis-i2c"
>>     #define TPM_IS_TIS_ISA(chr)                         \
>>       object_dynamic_cast(OBJECT(chr), TYPE_TPM_TIS_ISA)
>> @@ -57,6 +58,8 @@ struct TPMIfClass {
>>       object_dynamic_cast(OBJECT(chr), TYPE_TPM_CRB)
>>   #define TPM_IS_SPAPR(chr)                           \
>>       object_dynamic_cast(OBJECT(chr), TYPE_TPM_SPAPR)
>> +#define TPM_IS_TIS_I2C(chr)                      \
>> +    object_dynamic_cast(OBJECT(chr), TYPE_TPM_TIS_I2C)
>>     /* returns NULL unless there is exactly one TPM device */
>>   static inline TPMIf *tpm_find(void)
>