Re: [RFC PATCH v3 3/3] SPI: Add virtio SPI driver.

Mark Brown
2024-02-13T17:49:11Z

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On Tue, Feb 13, 2024 at 02:53:50PM +0100, Harald Mommer wrote:

> +/*
> + * See also
> + * https://lore.kernel.org/all/6171c1c3-55ba-4f74-ae60-764820cf1caf@quicinc.com
> + */
> +static int virtio_spi_set_delays(struct spi_transfer_head *th,
> + struct spi_device *spi,
> + struct spi_transfer *xfer)

Please write actual comments that can be read standalone, the reader has
absolutely no idea why they'd want to follow the link and there's
nothing being referenced by that "also".

> +static int virtio_spi_one_transfer(struct virtio_spi_req *spi_req,
> + struct spi_controller *ctrl,
> + struct spi_message *msg,
> + struct spi_transfer *xfer)

> + /*
> + * Got comment: "The virtio spec for cs_change is *not* what the Linux
> + * cs_change field does, this will not do the right thing."
> + * TODO: Understand/discuss this, still unclear what may be wrong here
> + */
> + th->cs_change = xfer->cs_change;

> +static int virtio_spi_transfer_one_message(struct spi_controller *ctrl,
> + struct spi_message *msg)
> +{
> + struct virtio_spi_priv *priv = spi_controller_get_devdata(ctrl);
> + struct virtio_spi_req *spi_req;
> + struct spi_transfer *xfer;
> + int ret = 0;
> +
> + spi_req = kzalloc(sizeof(*spi_req), GFP_KERNEL);
> + if (!spi_req) {
> + ret = -ENOMEM;
> + goto no_mem;
> + }

Why not just allocate this once, it's not like it's possible to send
more than one message simultaneously?

> + /*
> + * Simple implementation: Process message by message and wait for each
> + * message to be completed by the device side.
> + */
> + list_for_each_entry(xfer, &msg->transfers, transfer_list) {

This is processing transfers within a message rather than messages.

> + ret = virtio_spi_one_transfer(spi_req, ctrl, msg, xfer);
> + if (ret)
> + goto msg_done;
> +
> + virtqueue_kick(priv->vq);
> +
> + wait_for_completion(&spi_req->completion);
> +
> + /* Read result from message */
> + ret = (int)spi_req->result.result;
> + if (ret)
> + goto msg_done;

It's not clear why this isn't within _spi_transfer_one() and then we
don't just use a transfer_one() callback and factor everything out to
the core?

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