linux-kernel - Re: [RESEND PATCH 05/11] platform/chrome: cros_ec_proto: separate cros_ec_wait_until

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Message-ID: <CABXOdTeC+q-UiPiThqL5MGg-+cGACGW4qLaLKZbmX4M26TvbDg@mail.gmail.com>
Date:   Wed, 13 Jul 2022 11:15:47 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Tzung-Bi Shih <tzungbi@...nel.org>
Cc:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        "open list:CHROME HARDWARE PLATFORM SUPPORT" 
        <chrome-platform@...ts.linux.dev>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH 05/11] platform/chrome: cros_ec_proto: separate cros_ec_wait_until_complete()

On Mon, Jun 27, 2022 at 7:49 PM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> EC returns EC_RES_IN_PROGRESS if the host command needs more time to
> complete.  Whenever receives the return code, cros_ec_send_command()
> sends EC_CMD_GET_COMMS_STATUS to query the command status.
>
> Separate cros_ec_wait_until_complete() from cros_ec_send_command().
> It sends EC_CMD_GET_COMMS_STATUS and waits until the previous command
> was completed, or encountered error, or timed out.
>
> Signed-off-by: Tzung-Bi Shih <tzungbi@...nel.org>
> ---
>  drivers/platform/chrome/cros_ec_proto.c | 75 ++++++++++++-------------
>  1 file changed, 36 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
> index 0cec013be3d3..466ecb063bd6 100644
> --- a/drivers/platform/chrome/cros_ec_proto.c
> +++ b/drivers/platform/chrome/cros_ec_proto.c
> @@ -134,53 +134,50 @@ static int cros_ec_xfer_command(struct cros_ec_device *ec_dev, struct cros_ec_co
>         return ret;
>  }
>
> -static int cros_ec_send_command(struct cros_ec_device *ec_dev, struct cros_ec_command *msg)
> +static int cros_ec_wait_until_complete(struct cros_ec_device *ec_dev, uint32_t *result)
>  {
> -       int ret = cros_ec_xfer_command(ec_dev, msg);
> +       struct cros_ec_command *msg;
> +       struct ec_response_get_comms_status *status;
> +       int ret = 0, i;
> +
> +       msg = kzalloc(sizeof(*msg) + sizeof(*status), GFP_KERNEL);
> +       if (!msg)
> +               return -ENOMEM;

AFAICS this is always 24 bytes. I would suggest to allocate it on the
stack to reduce overhead.
>
> -       if (msg->result == EC_RES_IN_PROGRESS) {
> -               int i;
> -               struct cros_ec_command *status_msg;
> -               struct ec_response_get_comms_status *status;
> +       msg->command = EC_CMD_GET_COMMS_STATUS;
> +       msg->insize = sizeof(*status);
>
> -               status_msg = kmalloc(sizeof(*status_msg) + sizeof(*status),
> -                                    GFP_KERNEL);
> -               if (!status_msg)
> -                       return -ENOMEM;
> +       status = (struct ec_response_get_comms_status *)msg->data;
>
> -               status_msg->version = 0;
> -               status_msg->command = EC_CMD_GET_COMMS_STATUS;
> -               status_msg->insize = sizeof(*status);
> -               status_msg->outsize = 0;
> +       /* Query the EC's status until it's no longer busy or we encounter an error. */
> +       for (i = 0; i < EC_COMMAND_RETRIES; ++i) {
> +               usleep_range(10000, 11000);
>
> -               /*
> -                * Query the EC's status until it's no longer busy or
> -                * we encounter an error.
> -                */
> -               for (i = 0; i < EC_COMMAND_RETRIES; i++) {
> -                       usleep_range(10000, 11000);
> -
> -                       trace_cros_ec_request_start(status_msg);
> -                       ret = (*xfer_fxn)(ec_dev, status_msg);
> -                       trace_cros_ec_request_done(status_msg, ret);
> -                       if (ret == -EAGAIN)
> -                               continue;
> -                       if (ret < 0)
> -                               break;
> -
> -                       msg->result = status_msg->result;
> -                       if (status_msg->result != EC_RES_SUCCESS)
> -                               break;
> -
> -                       status = (struct ec_response_get_comms_status *)
> -                                status_msg->data;
> -                       if (!(status->flags & EC_COMMS_STATUS_PROCESSING))
> -                               break;
> -               }
> +               ret = cros_ec_xfer_command(ec_dev, msg);
> +               if (ret == -EAGAIN)
> +                       continue;
> +               if (ret < 0)
> +                       break;

With the command allocated on the stack, this can return immediately.

> +
> +               *result = msg->result;
> +               if (msg->result != EC_RES_SUCCESS)
> +                       break;

Again, this can return immediately if the command buffer is on the stack.

>
> -               kfree(status_msg);
> +               if (!(status->flags & EC_COMMS_STATUS_PROCESSING))
> +                       break;

Can return immediately.

>         }
>
> +       kfree(msg);
> +       return ret;

What should this return on timeout ?

> +}
> +
> +static int cros_ec_send_command(struct cros_ec_device *ec_dev, struct cros_ec_command *msg)
> +{
> +       int ret = cros_ec_xfer_command(ec_dev, msg);
> +
> +       if (msg->result == EC_RES_IN_PROGRESS)
> +               ret = cros_ec_wait_until_complete(ec_dev, &msg->result);
> +
>         return ret;
>  }
>
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>