Re: clarifying the handling of responses for virtio-rpmb

["Alex Bennée" <alex.bennee@linaro.org>]

Alex Bennée <alex.bennee@linaro.org> writes:

> Hi,
>
> The specification lists a number of commands that have responses:
>
>   The operation of a virtio RPMB device is driven by the requests placed
>   on the virtqueue. The type of request can be program key
>   (VIRTIO_RPMB_REQ_PROGRAM_KEY), get write counter
>   (VIRTIO_RPMB_REQ_GET_WRITE_COUNTER), write
>   (VIRTIO_RPMB_REQ_DATA_WRITE), and read (VIRTIO_RPMB_REQ_DATA_READ). A
>   program key or write request can also combine with a result read
>   (VIRTIO_RPMB_REQ_RESULT_READ) for a returned result.
>
> Now I'm deep in the guts of virt queues doing the implementation I'm
> trying to clarify exactly what frames should be sent to the device and
> if they should be out_sgs or in_sgs. I suspect there is some difference
> between the original prototype interface and what we have now.
>
> Some operations obviously have an implied response
> (VIRTIO_RPMB_REQ_GET_WRITE_COUNTER and VIRTIO_RPMB_REQ_DATA_READ). As
> far as I could tell the frame should be simple:
>
>   sg[0] (out_sg=1) - frame with command
>   sg[1..n] (in_sg=1..n) - space for the reply to be filled in by the device
>
> However the language for the program key and data write say they can be
> combined with a VIRTIO_RPMB_REQ_RESULT_READ to optionally return a
> result. My question is is this result read meant to be in a separate
> request frame and response frame so you get:
>
>  sg[0] - VIRTIO_RPMB_REQ_PROGRAM_KEY/VIRTIO_RPMB_REQ_DATA_WRITE frame
>  sg[1] - VIRTIO_RPMB_REQ_RESULT_READ (out_sg=2)
>  sg[2] - empty frame for response (in_sg=1)
>
> or:
>
>  sg[0] - VIRTIO_RPMB_REQ_PROGRAM_KEY/VIRTIO_RPMB_REQ_DATA_WRITE frame (out_sg=1)
>  sg[1] - VIRTIO_RPMB_REQ_RESULT_READ (in_sg=1)
>
> where the result frame is filled in and sent back?
>
> I must say I'm a little confused by the logic in rpmb_ioctl (in the
> userspace tool) which creates both out_frames and resp frames:
>
>   static int rpmb_ioctl(uint8_t frame_type, int fd, uint16_t req,
>                         const void *frames_in, unsigned int cnt_in,
>                         void *frames_out, unsigned int cnt_out)
>   {
>           int ret;
>           struct __packed {
>                   struct rpmb_ioc_seq_cmd h;
>                   struct rpmb_ioc_cmd cmd[3];
>           } iseq = {};
>
>           void *frame_res = NULL;
>           int i;
>           uint32_t flags;
>
>           rpmb_dbg("RPMB OP: %s\n", rpmb_op_str(req));
>           dbg_dump_frame(frame_type, "In Frame: ", frames_in, cnt_in);
>
>           i = 0;
>           flags = RPMB_F_WRITE;
>           if (req == RPMB_WRITE_DATA || req == RPMB_PROGRAM_KEY)
>                   flags |= RPMB_F_REL_WRITE;
>           rpmb_ioc_cmd_set(iseq.cmd[i], flags, frames_in, cnt_in);
>           i++;
>
>           if (req == RPMB_WRITE_DATA || req == RPMB_PROGRAM_KEY) {
>                   frame_res = rpmb_frame_alloc(frame_type, 0);
>                   if (!frame_res)
>                           return -ENOMEM;
>                   rpmb_frame_set(frame_type, frame_res,
>                                  RPMB_RESULT_READ, 0, 0, 0);
>                   rpmb_ioc_cmd_set(iseq.cmd[i], RPMB_F_WRITE, frame_res, 0);
>                   i++;
>           }
>
>           rpmb_ioc_cmd_set(iseq.cmd[i], 0, frames_out, cnt_out);
>           i++;
>
>           iseq.h.num_of_cmds = i;
>           ret = ioctl(fd, RPMB_IOC_SEQ_CMD, &iseq);
>           if (ret < 0)
>                   rpmb_err("ioctl failure %d: %s.\n", ret, strerror(errno));
>
>           ret = rpmb_check_req_resp(frame_type, req, frames_out);
>
>           dbg_dump_frame(frame_type, "Res Frame: ", frame_res, 1);
>           dbg_dump_frame(frame_type, "Out Frame: ", frames_out, cnt_out);
>           free(frame_res);
>           return ret;
>   }
>
> although I'm guessing this might just be an impedance between the
> chardev ioctl interface for rpmb and the virtio FE driver which is only
> one potential consumer of these rpmb ioc commands? 
>
> Can anyone clarify?

Ping?

-- 
Alex Bennée
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