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

Qiang Zhang
2024-12-23T07:45:59Z

On Mon, Dec 23, 2024 at 03:34:45PM +0800, Haixu Cui wrote:
> Hi @Qiang Zhang,
>
> Thank you for your comments, and please refer to my response below. I
> would co-work with Harald on this driver.

Great! I'm glad to see you push this work forward. Your comments below LGTM.

Thanks,
Qiang

>
> On 9/9/2024 8:59 PM, Qiang Zhang wrote:
> > Hi, Harald
> >
> > On Tue, Mar 26, 2024 at 12:28:12PM +0100, Harald Mommer wrote:
> > > From: Harald Mommer <harald.mommer@opensynergy.com>
> > >
> > > This is the virtio SPI Linux kernel driver.
> > >
> > > Signed-off-by: Harald Mommer <Harald.Mommer@opensynergy.com>
> > [...]
> > > +static int virtio_spi_probe(struct virtio_device *vdev)
> > > +{
> > > + struct device_node *np = vdev->dev.parent->of_node;
> > > + struct virtio_spi_priv *priv;
> > > + struct spi_controller *ctrl;
> > > + int err;
> > > + u32 bus_num;
> > > + u16 csi;
> > > +
> > > + ctrl = devm_spi_alloc_host(&vdev->dev, sizeof(*priv));
> > > + if (!ctrl)
> > > + return -ENOMEM;
> > > +
> > > + priv = spi_controller_get_devdata(ctrl);
> > > + priv->vdev = vdev;
> > > + vdev->priv = priv;
> > > + ctrl->dev.of_node = vdev->dev.of_node;
> >
> > To support ACPI, ACPI node of the controller needs to be set:
> >
> > /*
> > * Setup ACPI node for controlled devices which will be probed through
> > * ACPI.
> > */
> > ACPI_COMPANION_SET(&vdev->dev, ACPI_COMPANION(vdev->dev.parent));
> >
>
> Yes, will add in next patch.
>
> > > + dev_set_drvdata(&vdev->dev, ctrl);
> > > +
> > > + init_completion(&priv->spi_req.completion);
> > > +
> > > + err = of_property_read_u32(np, "spi,bus-num", &bus_num);
> > > + if (!err && bus_num <= S16_MAX)
> > > + ctrl->bus_num = (s16)bus_num;
> >
> > This is not the right way to fix bus number. You can use OF alias.
> > Also, to work with ACPI, we should use common API like
> > device_property_read_u32.
> >
>
> I agree with you, "spi,bus-num" should not be mandatory in the device tree.
>
> How about updating as follows:
>
> + err = device_property_read_u32(ctrl->dev, "spi,bus-num", &bus_num);
> + if (!err && bus_num <= S16_MAX)
> + ctrl->bus_num = (s16)bus_num;
> + else
> + ctrl->bus_num = -1;
>
> So if "spi,bus-num" not set, bus_num is initialized as -1, then in function
> spi_register_controller, bus_num will be reassigned by OF alias(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c?h=v6.13-rc4#n3287),
> or dynamic allocated(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c?h=v6.13-rc4#n3295).
>
>
> > > +
> > > + virtio_spi_read_config(vdev);
> > > +
> > > + ctrl->transfer_one = virtio_spi_transfer_one;
> > > +
> > > + err = virtio_spi_find_vqs(priv);
> > > + if (err) {
> > > + dev_err(&vdev->dev, "Cannot setup virtqueues\n");
> > > + return err;
> > > + }
> > > +
> > > + board_info.max_speed_hz = priv->max_freq_hz;
> > > + board_info.bus_num = (u16)ctrl->bus_num;
> > > +
> > > + if (!(priv->mode_func_supported & VIRTIO_SPI_CS_HIGH))
> > > + board_info.mode = SPI_MODE_0;
> > > + else
> > > + board_info.mode = SPI_MODE_0 | SPI_CS_HIGH;
> > > +
> > > + err = spi_register_controller(ctrl);
> > > + if (err) {
> > > + dev_err(&vdev->dev, "Cannot register controller\n");
> > > + goto err_return;
> > > + }
> > > +
> > > + if (vdev->dev.of_node) {
> > > + dev_dbg(&vdev->dev, "Final setup triggered by DT child node\n");
> > > + return 0;
> > > + }
> > How about ACPI path?
> > > +
> > > + /* Add chip selects to controller */
> > > + for (csi = 0; csi < ctrl->num_chipselect; csi++) {
> > > + dev_dbg(&vdev->dev, "Setting up CS=%u\n", csi);
> > > + board_info.chip_select = csi;
> > > +
> > > + if (!spi_new_device(ctrl, &board_info)) {
> > > + dev_err(&vdev->dev, "Cannot setup device %u\n", csi);
> > > + spi_unregister_controller(ctrl);
> > > + err = -ENODEV;
> > > + goto err_return;
> > > + }
> > > + }
> > Just enumerate SPI devices via DT/ACPI. And a fixed SPI modalias "spi-virtio"
> > is no better than match method from DT/ACPI.
>
> How about deleting the following code.
>
> + if (vdev->dev.of_node) {
> + dev_dbg(&vdev->dev, "Final setup triggered by DT child node\n");
> + return 0;
> + }
>
> + /* Add chip selects to controller */
> + for (csi = 0; csi < ctrl->num_chipselect; csi++) {
> + dev_dbg(&vdev->dev, "Setting up CS=%u\n", csi);
> + board_info.chip_select = csi;
> +
> + if (!spi_new_device(ctrl, &board_info)) {
> + dev_err(&vdev->dev, "Cannot setup device %u\n", csi);
> + spi_unregister_controller(ctrl);
> + err = -ENODEV;
> + goto err_return;
> + }
> + }
>
> Then we can use the ACPI implementation in https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c?h=v6.13-rc4#n3378.
>
> Also creating SPI devices statically based on the board info seems somewhat
> unreasonable. I agree that DT/ACPI are the only reasonable way to specify
> the SPI nodes.
>
>
> Thanks again
> Haixu Cui
>
> >
> > Thanks,
> > Qiang
>