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

Haixu Cui
2024-12-23T07:34:59Z

Hi @Qiang Zhang,

Thank you for your comments, and please refer to my response below.
I would co-work with Harald on this driver.

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