[STABLE 6.12/6.14] Bluetooth MediaTek controller reset fixes

["Geoffrey D. Bennett" <g@b4.vu>]

Hi stable@vger.kernel.org,

Could you please apply:

1. Commit a7208610761ae ("Bluetooth: btmtk: Remove resetting mt7921
before downloading the fw") to v6.12.x (it's already in
v6.14).

2. Commit 33634e2ab7c6 ("Bluetooth: btmtk: Remove the resetting step
before downloading the fw") to v6.12.x and v6.14.x.

These fixes address an issue with some audio interfaces failing to
initialise during boot on kernels 6.11+. As noted in my original
analysis below, the MediaTek Bluetooth controller reset increases the
device setup time from ~200ms to ~20s and can interfere with other USB
devices on the bus.

Thanks,
Geoffrey.

On Fri, Mar 28, 2025 at 08:44:49AM +1030, Geoffrey D. Bennett wrote:
> Hi all,
> 
> Sorry, I see that an identical patch has already been applied to
> bluetooth-next
> https://lore.kernel.org/linux-bluetooth/20250315022730.11071-1-hao.qin@mediatek.com/
> 
> While I'm glad the issue is being addressed, my original patch
> https://lore.kernel.org/linux-bluetooth/Z8ybV04CVUfVAykH@m.b4.vu/
> contained useful context and tags that didn't make it into the final
> commit.
> 
> For getting this fix into current kernel releases 6.12/6.13/6.14, I
> think the patch needs the "Cc: stable@vger.kernel.org" tag that was in
> my original submission but missing from Hao's. Since this is causing
> significant issues for users on kernels 6.11+ (audio interfaces
> failing to work), it's important this gets backported.
> 
> Hao, is this something you can do? I think the instructions at
> https://www.kernel.org/doc/html/v6.14/process/stable-kernel-rules.html#option-3
> need to be followed, but I've not done this before.
> 
> Thanks,
> Geoffrey.
> 
> On Fri, Mar 28, 2025 at 07:22:06AM +1030, Geoffrey D. Bennett wrote:
> > This reverts commit ccfc8948d7e4d93cab341a99774b24586717d89a.
> > 
> > The MediaTek Bluetooth controller reset that was added increases the
> > Bluetooth device setup time from ~200ms to ~20s and interferes with
> > other devices on the bus.
> > 
> > Three users (with Focusrite Scarlett 2nd Gen 6i6 and 3rd Gen Solo and
> > 4i4 audio interfaces) reported that since 6.11 (which added this
> > commit) their audio interface fails to initialise if connected during
> > boot. Two of the users confirmed they have an MT7922.
> > 
> > Errors like this are observed in dmesg for the audio interface:
> > 
> >   usb 3-4: parse_audio_format_rates_v2v3(): unable to find clock source (clock -110)
> >   usb 3-4: uac_clock_source_is_valid(): cannot get clock validity for id 41
> >   usb 3-4: clock source 41 is not valid, cannot use
> > 
> > The problem only occurs when both devices and kernel modules are
> > present and loaded during system boot, so it can be worked around by
> > connecting the audio interface after booting.
> > 
> > Fixes: ccfc8948d7e4 ("Bluetooth: btusb: mediatek: reset the controller before downloading the fw")
> > Closes: https://github.com/geoffreybennett/linux-fcp/issues/24
> > Bisected-by: Benedikt Ziemons <ben@rs485.network>
> > Tested-by: Benedikt Ziemons <ben@rs485.network>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
> > ---
> > Changelog:
> > 
> > v1 -> v2:
> > 
> > - Updated commit message with additional information.
> > - No change to this patch's diff.
> > - Dropped alternate patch that only reverted for 0x7922.
> > - Chris, Sean, Hao agreed to reverting the change:
> >   https://lore.kernel.org/linux-bluetooth/2025031352-octopus-quadrant-f7ca@gregkh/T/#m0b31a9a8e87b9499e1ec3370c08f03e43bfb54bf
> > 
> >  drivers/bluetooth/btmtk.c | 10 ----------
> >  1 file changed, 10 deletions(-)
> > 
> > diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
> > index 68846c5bd4f7..4390fd571dbd 100644
> > --- a/drivers/bluetooth/btmtk.c
> > +++ b/drivers/bluetooth/btmtk.c
> > @@ -1330,13 +1330,6 @@ int btmtk_usb_setup(struct hci_dev *hdev)
> >  		break;
> >  	case 0x7922:
> >  	case 0x7925:
> > -		/* Reset the device to ensure it's in the initial state before
> > -		 * downloading the firmware to ensure.
> > -		 */
> > -
> > -		if (!test_bit(BTMTK_FIRMWARE_LOADED, &btmtk_data->flags))
> > -			btmtk_usb_subsys_reset(hdev, dev_id);
> > -		fallthrough;
> >  	case 0x7961:
> >  		btmtk_fw_get_filename(fw_bin_name, sizeof(fw_bin_name), dev_id,
> >  				      fw_version, fw_flavor);
> > @@ -1345,12 +1338,9 @@ int btmtk_usb_setup(struct hci_dev *hdev)
> >  						btmtk_usb_hci_wmt_sync);
> >  		if (err < 0) {
> >  			bt_dev_err(hdev, "Failed to set up firmware (%d)", err);
> > -			clear_bit(BTMTK_FIRMWARE_LOADED, &btmtk_data->flags);
> >  			return err;
> >  		}
> > 
> > -		set_bit(BTMTK_FIRMWARE_LOADED, &btmtk_data->flags);
> > -
> >  		/* It's Device EndPoint Reset Option Register */
> >  		err = btmtk_usb_uhw_reg_write(hdev, MTK_EP_RST_OPT,
> >  					      MTK_EP_RST_IN_OUT_OPT);
> > --
> > 2.45.0
> > 
> > 
> >