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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Fri, 26 Mar 2021 14:43:54 -0700
Message-ID: <CABBYNZLmKF2x1PdXiqwBZ++DRRk_JrUDMedrg+yLe+sfrpuoOg@mail.gmail.com>
Subject: Re: [PATCH BlueZ] gatt: allow 'notify' and 'indicate' flags
To:     Alexander Haas <alexander.haas@expleogroup.com>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
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Hi Alexander,

On Fri, Mar 26, 2021 at 5:44 AM Alexander Haas
<alexander.haas@expleogroup.com> wrote:
>
> It is possible that some characteristics use the Notify as well as Indica=
te property.
> In this case the CCC value is 3 and BlueZ returns BT_ERROR_CCC_IMPROPERLY=
_CONFIGURED.
> This should be the behavior for values > 3.
> ---
>  src/gatt-database.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/src/gatt-database.c b/src/gatt-database.c
> index be6dfb265..8e16c1d79 100644
> --- a/src/gatt-database.c
> +++ b/src/gatt-database.c
> @@ -2648,9 +2648,9 @@ static uint8_t ccc_write_cb(struct pending_op *op, =
void *user_data)
>     return BT_ATT_ERROR_INSUFFICIENT_RESOURCES;
>
>   /* Don't support undefined CCC values yet */
> - if (value > 2 ||
> -   (value =3D=3D 1 && !(chrc->props & BT_GATT_CHRC_PROP_NOTIFY)) ||
> -   (value =3D=3D 2 && !(chrc->props & BT_GATT_CHRC_PROP_INDICATE)))
> + if (value > 3 ||
> +   (value & 0x1 && !(chrc->props & BT_GATT_CHRC_PROP_NOTIFY)) ||
> +   (value & 0x2 && !(chrc->props & BT_GATT_CHRC_PROP_INDICATE)))
>     return BT_ERROR_CCC_IMPROPERLY_CONFIGURED;
>
>   if (chrc->notify_io) {
> --
> 2.31.0

Looks like your email client has mangled your patch:

Applying: gatt: allow 'notify' and 'indicate' flags
error: corrupt patch at line 11
Patch failed at 0001 gatt: allow 'notify' and 'indicate' flags

I'm also curious about what client does require subscribing to
notification and indication at same time? This would lead to
duplicated data being sent as both notification and indication, also
since indication are queued until a confirmation is received
subscribing to both simultaneously may cause races:

PropertiesChanged: Value: 0xaa
ATT: Notify 0xaa
ATT: Indicate 0xaa

PropertiesChanged: Value: 0xbb
ATT: Notify 0xbb
(queued)[ATT: Indicate 0xaa]

PropertiesChanged: Value: 0xcc
ATT: Notify 0xcc
(queued)[ATT: Indicate 0xcc]

ATT: Confirm
ATT: Indicate 0xbb

ATT: Confirm
ATT: Indicate 0xcc

So the client may perceive the indication as rollbacks, so while this
may be valid according to the spec this can cause issues if not
handled correctly. If this is due different applications having
different subscription types, one wants to be notified and the other
indicated, then only indication shall be used.

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--=20
Luiz Augusto von Dentz