linux-kernel - Re: [PATCH v3 3/3] Bluetooth: Add ABI doc for sysfs isoc

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Message-ID: <CADg1FFcsYSM2SsyYULBzqmML67+4Hx9ipemACOv_oLCrwweiWg@mail.gmail.com>
Date: Wed, 12 Feb 2025 12:48:29 +0800
From: Hsin-chen Chuang <chharry@...gle.com>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: linux-bluetooth@...r.kernel.org, 
	chromeos-bluetooth-upstreaming@...omium.org, 
	Hsin-chen Chuang <chharry@...omium.org>, Johan Hedberg <johan.hedberg@...il.com>, 
	Marcel Holtmann <marcel@...tmann.org>, linux-kernel@...r.kernel.org, 
	Ying Hsu <yinghsu@...omium.org>
Subject: Re: [PATCH v3 3/3] Bluetooth: Add ABI doc for sysfs isoc_alt

Hi Luiz,

Thanks, that makes sense to me. I'll resolve this comment in the next version.

On Wed, Feb 12, 2025 at 6:01 AM Luiz Augusto von Dentz
<luiz.dentz@...il.com> wrote:
>
> Hi Hsin-chen,
>
> On Mon, Feb 10, 2025 at 11:23 PM Hsin-chen Chuang <chharry@...gle.com> wrote:
> >
> > Hi Luiz,
> >
> > Thanks for the feedback.
> >
> > On Tue, Feb 11, 2025 at 2:17 AM Luiz Augusto von Dentz
> > <luiz.dentz@...il.com> wrote:
> > >
> > > Hi Hsin-chen,
> > >
> > > On Mon, Feb 10, 2025 at 5:32 AM Hsin-chen Chuang <chharry@...gle.com> wrote:
> > > >
> > > > From: Hsin-chen Chuang <chharry@...omium.org>
> > > >
> > > > The functionality was completed in commit 5e5c3898ef49 ("Bluetooth: Fix
> > > > possible race with userspace of sysfs isoc_alt")
> > > >
> > > > Fixes: 5e5c3898ef49 ("Bluetooth: Fix possible race with userspace of sysfs isoc_alt")
> > > > Signed-off-by: Hsin-chen Chuang <chharry@...omium.org>
> > > > ---
> > > >
> > > > (no changes since v1)
> > > >
> > > >  Documentation/ABI/stable/sysfs-class-bluetooth | 12 ++++++++++++
> > > >  1 file changed, 12 insertions(+)
> > > >
> > > > diff --git a/Documentation/ABI/stable/sysfs-class-bluetooth b/Documentation/ABI/stable/sysfs-class-bluetooth
> > > > index 36be02471174..1168e0318e35 100644
> > > > --- a/Documentation/ABI/stable/sysfs-class-bluetooth
> > > > +++ b/Documentation/ABI/stable/sysfs-class-bluetooth
> > > > @@ -7,3 +7,15 @@ Description:   This write-only attribute allows users to trigger the vendor reset
> > > >                 The reset may or may not be done through the device transport
> > > >                 (e.g., UART/USB), and can also be done through an out-of-band
> > > >                 approach such as GPIO.
> > > > +
> > > > +What:          /sys/class/bluetooth/hci<index>/isoc_alt
> > > > +Date:          10-Feb-2025
> > > > +KernelVersion: 6.13
> > > > +Contact:       linux-bluetooth@...r.kernel.org
> > > > +Description:   This attribute allows users to configure the USB Alternate setting
> > > > +               for the specific HCI device. Reading this attribute returns the
> > > > +               current setting, and writing any supported numbers would change
> > > > +               the setting. See the USB Alternate setting definition in Bluetooth
> > > > +               core spec 5, vol 4, part B, table 2.1.
> > > > +               If the data is not a valid number, the write fails with -EINVAL.
> > > > +               The other failures are vendor specific.
> > >
> > > Still not really convinced this is the right way to expose it, it is
> > > not an HCI attribute to begin with, not sure if we couldn't perhaps
> >
> > Could you tell more about why this is not an HCI attr to begin with?
> > The alt setting is bonded to the USB device which is now under btusb's
> > control, and btusb creates a sysfs node for this. This attr location
> > decision seems natural to me.
>
> Well alt setting is (obviously) not covered as part of HCI
> specification, USB is one possible transport bus of HCI, but that
> itself is already saying that we would be mixing the transport with
> actual HCI protocol.
>
> > > add another node to control it or add via USB device?
> >
> > I feel allowing this in the USB sysfs API might be an overkill as that
> > makes all USB devices' alt settings be controllable from the user
> > space. Limiting this usage in the scope of BT makes more sense to me.
>
> Not all, just btusb ones, that said what we could add another level to
> control transport specific attribute e.g
> /sys/class/bluetooth/usb#/isoc_alt than that becomes the parent of
> /sys/class/bluetooth/hci<index>
>
> > >
> > > --
> > > Luiz Augusto von Dentz
> >
> > --
> > Best Regards,
> > Hsin-chen
>
>
>
> --
> Luiz Augusto von Dentz