linux-kernel - Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power

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Message-ID: <20211117124717.12352-1-redecorating@protonmail.com>
Date:   Wed, 17 Nov 2021 12:48:36 +0000
From:   Orlando Chamberlain <redecorating@...tonmail.com>
To:     regressions@...mhuis.info
Cc:     danielwinkler@...gle.com, gargaditya08@...e.com,
        gregkh@...uxfoundation.org, johan.hedberg@...el.com,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        luiz.dentz@...il.com, marcel@...tmann.org,
        redecorating@...tonmail.com, regressions@...ts.linux.dev,
        sonnysasaka@...omium.org
Subject: Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power

> So if this just affects two macs, why can't the fix be realized as a
> quirk that is only enabled on those two systems? Or are they impossible
> to detect clearly via DMI data or something like that?

I think we should be able to quirk based off the acpi _CID "apple-uart-blth"
or _HID "BCM2E7C". Marcel suggested quirking based of the acpi table here
https://lore.kernel.org/linux-bluetooth/1D2217A9-EA73-4D93-8D0B-5BC2718D4788@holtmann.org/

This would catch some unaffected Macs, but they don't support the LE Read
Transmit Power command anyway (the affected macs were released after it
was added to the Bluetooth spec, while the unaffected Macs were released
before it was added to the spec, and thus don't support it).

I'm not sure how to go about applying a quirk based off this, there are
quirks in drivers/bluetooth/hci_bcm.c (no_early_set_baudrate and
drive_rts_on_open), but they don't seem to be based off acpi ids.

It might be simpler to make it ignore the Unknown Command error, like
in this patch https://lore.kernel.org/linux-bluetooth/CABBYNZLjSfcG_KqTEbL6NOSvHhA5-b1t_S=3FQP4=GwW21kuzg@mail.gmail.com/
however that only applies on bluetooth-next and needed the status it
checks for to be -56, not 0x01.

--
Thanks,
Orlando