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Date: Sun, 25 Apr 2021 17:52:47 +0200
From: Lars-Peter Clausen <lars@...afoo.de>
To: Tomasz Duszynski <tomasz.duszynski@...akon.com>,
linux-iio@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
jic23@...nel.org, robh+dt@...nel.org
Subject: Re: [PATCH 2/3] iio: sps30: add support for serial interface
On 4/25/21 3:55 PM, Tomasz Duszynski wrote:
> [...]
>
> +struct sps30_serial_priv {
> + struct completion new_frame;
> + char buf[SPS30_SERIAL_MAX_BUF_SIZE];
The driver uses char, but the serdev API uses unsigned char. Just to
avoid any surprises I'd use unsigned char for all the buffers in the
driver as well.
> + int num;
> + unsigned int chksum;
> + bool escaped;
> + bool done;
> +};
> +
> +static int sps30_serial_xfer(struct sps30_state *state, const char *buf, int size)
> +{
> + struct serdev_device *serdev = to_serdev_device(state->dev);
> + struct sps30_serial_priv *priv = state->priv;
> + int ret;
> +
> + priv->num = 0;
> + priv->chksum = 0;
> + priv->escaped = false;
> + priv->done = false;
Hm... no locking with regards to the serdev callback. I guess the
assumption is that we'll never receive any data without explicitly
requesting it.
> +
> + ret = serdev_device_write(serdev, buf, size, SPS30_SERIAL_TIMEOUT);
> + if (ret < 0)
> + return ret;
> + if (ret != size)
> + return -EIO;
> +
> + ret = wait_for_completion_interruptible_timeout(&priv->new_frame, SPS30_SERIAL_TIMEOUT);
> + if (ret < 0)
> + return ret;
> + if (!ret)
> + return -ETIMEDOUT;
> +
> + return 0;
> +}
> [...]
> +static bool sps30_serial_frame_valid(struct sps30_state *state, const char *buf)
> +{
> + struct sps30_serial_priv *priv = state->priv;
> +
> + if ((priv->num < SPS30_SERIAL_FRAME_MIN_SIZE) ||
> + (priv->num != SPS30_SERIAL_FRAME_MIN_SIZE +
> + priv->buf[SPS30_SERIAL_FRAME_MISO_LEN_OFFSET])) {
> + dev_err(state->dev, "frame has invalid number of bytes\n");
> + return false;
> + }
> +
> + if ((priv->buf[SPS30_SERIAL_FRAME_ADR_OFFSET] != buf[SPS30_SERIAL_FRAME_ADR_OFFSET]) ||
> + (priv->buf[SPS30_SERIAL_FRAME_CMD_OFFSET] != buf[SPS30_SERIAL_FRAME_CMD_OFFSET])) {
> + dev_err(state->dev, "frame has wrong ADR and CMD bytes\n");
> + return false;
> + }
> +
> + if (priv->buf[SPS30_SERIAL_FRAME_MISO_STATE_OFFSET]) {
> + dev_err(state->dev, "frame with non-zero state received (0x%02x)\n",
> + priv->buf[SPS30_SERIAL_FRAME_MISO_STATE_OFFSET]);
> + //return false;
What's with the out commented line?
> + }
> +
> + if (priv->buf[priv->num - 2] != priv->chksum) {
> + dev_err(state->dev, "frame integrity check failed\n");
> + return false;
> + }
> +
> + return true;
> +}
> +
> +static int sps30_serial_command(struct sps30_state *state, char cmd, void *arg, int arg_size,
> + void *rsp, int rsp_size)
> +{
> + struct sps30_serial_priv *priv = state->priv;
> + char buf[SPS30_SERIAL_MAX_BUF_SIZE];
> + int ret, size;
> +
> + size = sps30_serial_prep_frame(buf, cmd, arg, arg_size);
> + ret = sps30_serial_xfer(state, buf, size);
> + if (ret)
> + return ret;
> +
> + if (!sps30_serial_frame_valid(state, buf))
> + return -EIO;
> +
> + if (rsp) {
> + rsp_size = clamp((int)priv->buf[SPS30_SERIAL_FRAME_MISO_LEN_OFFSET], 0, rsp_size);
If buf is unsigned char this can be a min_t(unsigned int, ...). And
maybe also make rsp_size unsigned int.
> + memcpy(rsp, &priv->buf[SPS30_SERIAL_FRAME_MISO_DATA_OFFSET], rsp_size);
> + }
> +
> + return rsp_size;
> +}
> +
> +static int sps30_serial_receive_buf(struct serdev_device *serdev, const unsigned char *buf,
> + size_t size)
> +{
> + struct iio_dev *indio_dev = dev_get_drvdata(&serdev->dev);
> + struct sps30_serial_priv *priv;
> + struct sps30_state *state;
> + unsigned char byte;
> + int i;
> +
> + if (!indio_dev)
> + return 0;
> +
> + state = iio_priv(indio_dev);
> + priv = state->priv;
> +
> + /* just in case device put some unexpected data on the bus */
> + if (priv->done)
> + return size;
> +
> + /* wait for the start of frame */
> + if (!priv->num && size && buf[0] != SPS30_SERIAL_SOF_EOF)
> + return 1;
> +
> + if (priv->num + size >= ARRAY_SIZE(priv->buf))
> + size = ARRAY_SIZE(priv->buf) - priv->num;
> +
> + for (i = 0; i < size; i++) {
> + byte = buf[i];
> + /* remove stuffed bytes on-the-fly */
> + if (byte == SPS30_SERIAL_ESCAPE_CHAR) {
> + priv->escaped = true;
> + continue;
> + }
> +
> + byte = sps30_serial_get_byte(priv->escaped, byte);
> + if (priv->escaped && !byte)
> + dev_warn(state->dev, "unrecognized escaped char (0x%02x)\n", byte);
> + priv->chksum += byte;
> + /* incrementing here would complete rx just after reading SOF */
> + priv->buf[priv->num] = byte;
> +
> + if (priv->num++ && !priv->escaped && byte == SPS30_SERIAL_SOF_EOF) {
This is a bit to tricky for my taste.
How about.
priv->num++
if (priv->num > 1 && ...)
> + /* SOF, EOF and checksum itself are not checksummed */
> + priv->chksum -= 2 * SPS30_SERIAL_SOF_EOF + priv->buf[priv->num - 2];
> + priv->chksum = (unsigned char)~priv->chksum;
To keep the whole checksum stuff simpler, maybe just compute it in
sps30_serial_frame_valid() over the whole set of data.
> + priv->done = true;
> + complete(&priv->new_frame);
> + i++;
> + break;
> + }
> +
> + priv->escaped = false;
> + }
> +
> + return i;
> +}
> [...]
> +static int sps30_serial_probe(struct serdev_device *serdev)
> +{
> [...]
> + return sps30_probe(dev, KBUILD_MODNAME, priv, &sps30_serial_ops);
Usually the IIO device name should just be the part number. Ideally the
application should not care about the backend. I'd just pass "sps30"
here for the name.
> +}
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