Re: [PATCH v3 2/3] hw/i2c: add mctp core

[Jonathan Cameron]

On Wed, 31 May 2023 13:47:43 +0200
Klaus Jensen <its@irrelevant.dk> wrote:

> From: Klaus Jensen <k.jensen@samsung.com>
> 
> Add an abstract MCTP over I2C endpoint model. This implements MCTP
> control message handling as well as handling the actual I2C transport
> (packetization).
> 
> Devices are intended to derive from this and implement the class
> methods.
> 
> Parts of this implementation is inspired by code[1] previously posted by
> Jonathan Cameron.
> 
> Squashed a fix[2] from Matt Johnston.
> 
>   [1]: 
> https://lore.kernel.org/qemu-devel/20220520170128.4436-1-Jonathan.Cameron@huawei.com/
>   [2]: 
> https://lore.kernel.org/qemu-devel/20221121080445.GA29062@codeconstruct.com.au/
> 
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Hi Klaus,

A few minor comments inline.

With those tidied up feel free to add
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>



> +
> +        if (pkt->mctp.hdr.flags & MCTP_H_FLAGS_SOM) {
> +            mctp->tx.is_control = false;
> +
> +            if (mctp->state == I2C_MCTP_STATE_RX) {
> +                mc->reset(mctp);
> +            }
> +
> +            mctp->state = I2C_MCTP_STATE_RX;
> +
> +            mctp->tx.addr = pkt->i2c.source;
> +            mctp->tx.eid = pkt->mctp.hdr.eid.source;
> +            mctp->tx.flags = pkt->mctp.hdr.flags & 0x7;

Maybe worth either defining that mask, or adding a comment that this
is copying the msg tag.  Or rename flags...


> +            mctp->tx.pktseq = (pkt->mctp.hdr.flags >> 4) & 0x3;
> +
> +            if ((pkt->mctp.payload[0] & 0x7f) == MCTP_MESSAGE_TYPE_CONTROL) {
> +                mctp->tx.is_control = true;
> +
> +                i2c_mctp_handle_control(mctp);
> +
> +                return 0;
> +            }
> +        } else if (mctp->state == I2C_MCTP_STATE_RX_STARTED) {
> +            trace_i2c_mctp_drop_expected_som();
> +            goto drop;
> +        } else if (((pkt->mctp.hdr.flags >> 4) & 0x3) != (++mctp->tx.pktseq 
> & 0x3)) {
> +            trace_i2c_mctp_drop_invalid_pktseq((pkt->mctp.hdr.flags >> 4) & 
> 0x3,
> +                                               mctp->tx.pktseq & 0x3);
> +            goto drop;
> +        }
> +
> +        mc->put_buf(mctp, i2c_mctp_payload(mctp->buffer), payload_len);
> +
> +        if (pkt->mctp.hdr.flags & MCTP_H_FLAGS_EOM) {
> +            mc->handle(mctp);
> +            mctp->state = I2C_MCTP_STATE_WAIT_TX;
> +        }
> +
> +        return 0;
> +
> +    default:
> +        return -1;
> +    }
> +
> +drop:
> +    mc->reset(mctp);
> +
> +    mctp->state = I2C_MCTP_STATE_IDLE;
> +
> +    return 0;
> +}


> diff --git a/include/hw/i2c/mctp.h b/include/hw/i2c/mctp.h
> new file mode 100644
> index 000000000000..ea97792e8d43
> --- /dev/null
> +++ b/include/hw/i2c/mctp.h

...
> +struct MCTPI2CEndpointClass {
> +    I2CSlaveClass parent_class;
> +
> +    /**
> +     *
> +     * put_buf() - receive incoming message fragment
> +     *
> +     * Must returns 0 for succes or -1 for error.
> +     */
> +    int (*put_buf)(MCTPI2CEndpoint *mctp, uint8_t *buf, size_t len);
> +
> +    /**
> +     * get_buf() - provide pointer to message fragment
> +     *
> +     * Called by the mctp subsystem to request a pointer to the next message
> +     * fragment. The implementation must advance its internal position such
> +     * that successive calls returns the next fragments.
> +     *
> +     * Must return the number of bytes available.
> +     */
> +    size_t (*get_buf)(MCTPI2CEndpoint *mctp, const uint8_t **buf,
> +                      size_t maxlen, uint8_t *mctp_flags);
> +
> +    /**
> +     * handle() - handle an MCTP message
> +     *
> +     * Called by the mctp subsystem when a full message has been delivered 
> and
> +     * may be parsed and processed.
> +     */
> +    void (*handle)(MCTPI2CEndpoint *mctp);
> +
> +    /**
> +     * reset() - reset internal state
> +     *
> +     * Called by the mctp subsystem in the event of some transport error.
> +     * Implementation must reset its internal state and drop any fragments
> +     * previously receieved.
> +     */
> +    void (*reset)(MCTPI2CEndpoint *mctp);
> +
> +    /**
> +     * get_types() - provide supported mctp message types
> +     *
> +     * Must provide a buffer with a full MCTP supported message types payload
> +     * (i.e. `0x0(SUCCESS),0x1(ONE),0x4(NMI)`).

ONE?  Looks to be PLDM
Good to reference DSP0239 Management Component Transport Protocol (MCTP) IDs 
and Codes
which has the list.

> +     *
> +     * Returns the size of the response.
> +     */
> +    size_t (*get_types)(MCTPI2CEndpoint *mctp, const uint8_t **data);
> +};

> diff --git a/include/net/mctp.h b/include/net/mctp.h
> new file mode 100644
> index 000000000000..70b49235ddb2
> --- /dev/null
> +++ b/include/net/mctp.h
> @@ -0,0 +1,28 @@
> +#ifndef QEMU_MCTP_H
> +#define QEMU_MCTP_H
> +
> +#define MCTP_BASELINE_MTU 64

Ideally add a reference for this as well.

8.3.1 Baseline transmission unit in DSP0236 1.3.0
> +
> +enum {
> +    MCTP_H_FLAGS_EOM = 1 << 6,
> +    MCTP_H_FLAGS_SOM = 1 << 7,

Trivial: I'm not really seeing the enum here as useful vs
a pair of defines.

> +};
> +
> +#define MCTP_MESSAGE_IC (1 << 7)
> +