Introduce hw.ubt.usb_isoc_enable loader tunable to disable isochronous transfer.

[naito.yuichiro_gmail.com]

Summary

This patch is a workaround for PR #238235.
If users want to disable isochronous transfer on ubt (like me), set loader tunable hw.ubt.usb_isoc_enable=0.
The default value of hw.ubt.usb_isoc_enable is 1 that works as same as before.
And the value of hw.ubt.usb_isoc_enable can be seen by sysctl.

Test Plan

hw.ubt.usb_isoc_enable=0 stops interrupt storms.

[• hselasky]

sys/netgraph/bluetooth/drivers/ubt/ng_ubt.c

157

Should be CTLFLAG_RWTUN .

1560

This might get out of sync.

Please remove this "if" and ensure xfer pointers are checked for NULL.

[• hselasky]

isochronous_transfer -> usb_isoc_enable

[naito.yuichiro_gmail.com]

Thanks for the comments.
I updated my patch that includes following fixes.

1. Do not change ubt_task() implementation, and check if sc_xfer is NULL in the ubt_xfer_start macro. So that make it easy to keep consistent with usbd_transfer_setup() in ubt_attach function.

2. ubt sysctl variable flag changed to CTLFLAG_RDTUN.

3. sysctl variable name changed to usb_isoc_enable.

I also updated the title of this review and summary context.

[• hselasky]

sys/netgraph/bluetooth/drivers/ubt/ng_ubt.c

144

usbd_transfer_start() is already NULL safe. No need to check for NULL here!

157

nodes should be CTLFLAG_RW

[naito.yuichiro_gmail.com]

sys/netgraph/bluetooth/drivers/ubt/ng_ubt.c

144

Ah,OK. I see the usbd_transfer_start() code.I will revert this macro change.

157

I will change to CTLFLAG_RW.

[naito.yuichiro_gmail.com]

• Revert usbd_transfer_start macro change. As a result, nothing changed from original.
• Use CTLFLAG_RW flag for sysctl node.

[• hselasky]

sys/netgraph/bluetooth/drivers/ubt/ng_ubt.c

160

, 1, should just be , 0, . This field is only used for constants.

--HPS

[naito.yuichiro_gmail.com]

sys/netgraph/bluetooth/drivers/ubt/ng_ubt.c

160

OK. I'll change to , 0,.

[naito.yuichiro_gmail.com]

• change val argument of SYSCTL_INT macro to 0.