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References: <20201209010030.342632-1-sonnysasaka@chromium.org> <20201209010030.342632-2-sonnysasaka@chromium.org>
In-Reply-To: <20201209010030.342632-2-sonnysasaka@chromium.org>
From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Tue, 8 Dec 2020 17:57:57 -0800
Message-ID: <CABBYNZ+OrbUb8YT8tYuFLVuhuTp9nhMdp_Jc0UyUO2a71rcBbw@mail.gmail.com>
Subject: Re: [PATCH BlueZ 2/2] input/hog: Cache the HID report map
To:     Sonny Sasaka <sonnysasaka@chromium.org>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>,
        Alain Michaud <alainm@chromium.org>
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Precedence: bulk

Hi Sonny,

On Tue, Dec 8, 2020 at 5:16 PM Sonny Sasaka <sonnysasaka@chromium.org> wrote:
>
> To optimize BLE HID devices reconnection response, we can cache the
> report map so that the subsequent reconnections do not need round trip
> time to read the report map.

While the idea is pretty good we need to find a way to persist it
across reboots/restarts. In theory we could save the value on the
gatt_db instance and then make changes to device.c:store_desc to
attempt to read if there is a value stored in the db save it on file
as well so the next time the cache is loaded it should restore the
report map, or any other descriptor that have its value saved in the
database. That said we may need to introduce some sort of property for
values stored in the db since normally the values store in the
database shall not be persisted on file, in fact it would cause a lot
of fime access updating the cache if we were to trigger updates
everytime the db is updated with a value.

> Reviewed-by: Alain Michaud <alainm@chromium.org>
>
> ---
>  profiles/input/hog-lib.c | 142 ++++++++++++++++++++++++++-------------
>  1 file changed, 96 insertions(+), 46 deletions(-)
>
> diff --git a/profiles/input/hog-lib.c b/profiles/input/hog-lib.c
> index ee811d301..1e198ea64 100644
> --- a/profiles/input/hog-lib.c
> +++ b/profiles/input/hog-lib.c
> @@ -95,6 +95,8 @@ struct bt_hog {
>         struct queue            *bas;
>         GSList                  *instances;
>         struct queue            *gatt_op;
> +       uint8_t                 report_map[HOG_REPORT_MAP_MAX_SIZE];
> +       ssize_t                 report_map_len;
>  };
>
>  struct report {
> @@ -276,6 +278,8 @@ static void find_included(struct bt_hog *hog, GAttrib *attrib,
>         free(req);
>  }
>
> +static void uhid_create(struct bt_hog *hog);
> +
>  static void report_value_cb(const guint8 *pdu, guint16 len, gpointer user_data)
>  {
>         struct report *report = user_data;
> @@ -924,57 +928,17 @@ static char *item2string(char *str, uint8_t *buf, uint8_t len)
>         return str;
>  }
>
> -static void report_map_read_cb(guint8 status, const guint8 *pdu, guint16 plen,
> -                                                       gpointer user_data)
> +static void uhid_create(struct bt_hog *hog)
>  {
> -       struct gatt_request *req = user_data;
> -       struct bt_hog *hog = req->user_data;
> -       uint8_t value[HOG_REPORT_MAP_MAX_SIZE];
>         struct uhid_event ev;
> -       ssize_t vlen;
> -       char itemstr[20]; /* 5x3 (data) + 4 (continuation) + 1 (null) */
> -       int i, err;
>         GError *gerr = NULL;
> +       int i, err;
>
> -       destroy_gatt_req(req);
> -
> -       DBG("HoG inspecting report map");
> -
> -       if (status != 0) {
> -               error("Report Map read failed: %s", att_ecode2str(status));
> -               return;
> -       }
> -
> -       vlen = dec_read_resp(pdu, plen, value, sizeof(value));
> -       if (vlen < 0) {
> -               error("ATT protocol error");
> +       if (!hog->report_map_len) {
> +               warn("Failed to initiate UHID_CREATE without report map");
>                 return;
>         }
>
> -       DBG("Report MAP:");
> -       for (i = 0; i < vlen;) {
> -               ssize_t ilen = 0;
> -               bool long_item = false;
> -
> -               if (get_descriptor_item_info(&value[i], vlen - i, &ilen,
> -                                                               &long_item)) {
> -                       /* Report ID is short item with prefix 100001xx */
> -                       if (!long_item && (value[i] & 0xfc) == 0x84)
> -                               hog->has_report_id = TRUE;
> -
> -                       DBG("\t%s", item2string(itemstr, &value[i], ilen));
> -
> -                       i += ilen;
> -               } else {
> -                       error("Report Map parsing failed at %d", i);
> -
> -                       /* Just print remaining items at once and break */
> -                       DBG("\t%s", item2string(itemstr, &value[i], vlen - i));
> -                       break;
> -               }
> -       }
> -
> -       /* create uHID device */
>         memset(&ev, 0, sizeof(ev));
>         ev.type = UHID_CREATE;
>
> @@ -1004,8 +968,8 @@ static void report_map_read_cb(guint8 status, const guint8 *pdu, guint16 plen,
>         ev.u.create.version = hog->version;
>         ev.u.create.country = hog->bcountrycode;
>         ev.u.create.bus = BUS_BLUETOOTH;
> -       ev.u.create.rd_data = value;
> -       ev.u.create.rd_size = vlen;
> +       ev.u.create.rd_data = hog->report_map;
> +       ev.u.create.rd_size = hog->report_map_len;
>
>         err = bt_uhid_send(hog->uhid, &ev);
>         if (err < 0) {
> @@ -1018,6 +982,62 @@ static void report_map_read_cb(guint8 status, const guint8 *pdu, guint16 plen,
>         bt_uhid_register(hog->uhid, UHID_SET_REPORT, set_report, hog);
>
>         hog->uhid_created = true;
> +}
> +
> +static void report_map_read_cb(guint8 status, const guint8 *pdu, guint16 plen,
> +                                                       gpointer user_data)
> +{
> +       struct gatt_request *req = user_data;
> +       struct bt_hog *hog = req->user_data;
> +       ssize_t vlen;
> +       char itemstr[20]; /* 5x3 (data) + 4 (continuation) + 1 (null) */
> +       int i;
> +
> +       destroy_gatt_req(req);
> +
> +       DBG("HoG inspecting report map");
> +
> +       if (status != 0) {
> +               error("Report Map read failed: %s", att_ecode2str(status));
> +               return;
> +       }
> +
> +       vlen = dec_read_resp(pdu, plen, hog->report_map,
> +                                               sizeof(hog->report_map));
> +       if (vlen < 0) {
> +               error("ATT protocol error");
> +               return;
> +       }
> +
> +       hog->report_map_len = vlen;
> +
> +       DBG("Report MAP:");
> +       for (i = 0; i < vlen;) {
> +               ssize_t ilen = 0;
> +               bool long_item = false;
> +
> +               if (get_descriptor_item_info(&hog->report_map[i], vlen - i,
> +                                               &ilen, &long_item)) {
> +                       /* Report ID is short item with prefix 100001xx */
> +                       if (!long_item && (hog->report_map[i] & 0xfc) == 0x84)
> +                               hog->has_report_id = TRUE;
> +
> +                       DBG("\t%s", item2string(itemstr, &hog->report_map[i],
> +                                                                       ilen));
> +
> +                       i += ilen;
> +               } else {
> +                       error("Report Map parsing failed at %d", i);
> +
> +                       /* Just print remaining items at once and break */
> +                       DBG("\t%s", item2string(itemstr, &hog->report_map[i],
> +                                               vlen - i));
> +                       break;
> +               }
> +       }
> +
> +       /* create uHID device */
> +       uhid_create(hog);
>
>         DBG("HoG created uHID device");
>  }
> @@ -1602,6 +1622,12 @@ bool bt_hog_attach(struct bt_hog *hog, void *gatt)
>                 bt_hog_attach(instance, gatt);
>         }
>
> +       /* Try to initiate UHID_CREATE if we already have the report map to
> +        * avoid re-reading the report map from the peer device.
> +        */
> +       if (hog->report_map_len > 0)
> +               uhid_create(hog);
> +
>         if (!hog->uhid_created) {
>                 DBG("HoG discovering characteristics");
>                 if (hog->attr)
> @@ -1627,6 +1653,29 @@ bool bt_hog_attach(struct bt_hog *hog, void *gatt)
>         return true;
>  }
>
> +static void uhid_destroy(struct bt_hog *hog)
> +{
> +       int err;
> +       struct uhid_event ev;
> +
> +       if (!hog->uhid_created)
> +               return;
> +
> +       bt_uhid_unregister_all(hog->uhid);
> +
> +       memset(&ev, 0, sizeof(ev));
> +       ev.type = UHID_DESTROY;
> +
> +       err = bt_uhid_send(hog->uhid, &ev);
> +
> +       if (err < 0) {
> +               error("bt_uhid_send: %s", strerror(-err));
> +               return;
> +       }
> +
> +       hog->uhid_created = false;
> +}
> +
>  void bt_hog_detach(struct bt_hog *hog)
>  {
>         GSList *l;
> @@ -1660,6 +1709,7 @@ void bt_hog_detach(struct bt_hog *hog)
>         queue_foreach(hog->gatt_op, (void *) cancel_gatt_req, NULL);
>         g_attrib_unref(hog->attrib);
>         hog->attrib = NULL;
> +       uhid_destroy(hog);
>  }
>
>  int bt_hog_set_control_point(struct bt_hog *hog, bool suspend)
> --
> 2.26.2
>


-- 
Luiz Augusto von Dentz