Return-Path: <cyrus@holtmann.org>
Subject: Re: Does anybody know conn->power_save variable in hci_conn.c?
From: Marcel Holtmann <marcel@holtmann.org>
To: Chan-Yeol Park <chanyeol.park@samsung.com>
Cc: linux-bluetooth@vger.kernel.org
In-Reply-To: <002e01c9fedc$f5fcb790$e1f626b0$%park@samsung.com>
References: <002e01c9fedc$f5fcb790$e1f626b0$%park@samsung.com>
Content-Type: text/plain
Date: Tue, 07 Jul 2009 10:36:49 -0700
Message-Id: <1246988209.3384.10.camel@localhost.localdomain>
Mime-Version: 1.0
Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Chan-Yeol,

> /*bluetooth kernel hci_conn.c */
> 382 void hci_conn_enter_active_mode(struct hci_conn *conn)
> 383 {
> 384         struct hci_dev *hdev = conn->hdev;
> 385
> 386         BT_DBG("conn %p mode %d", conn, conn->mode);
> 387
> 388         if (test_bit(HCI_RAW, &hdev->flags))
> 389                 return;
> 390
> 391         if (conn->mode != HCI_CM_SNIFF || !conn->power_save)
> 392                 goto timer;
> 393 
> 394         if (!test_and_set_bit(HCI_CONN_MODE_CHANGE_PEND, &conn->pend)) {
> 395                 struct hci_cp_exit_sniff_mode cp;
> 396                 cp.handle = __cpu_to_le16(conn->handle);
> 397                 hci_send_cmd(hdev, OGF_LINK_POLICY,
> 398                                 OCF_EXIT_SNIFF_MODE, sizeof(cp), &cp);
> 399         }
> 400
> 401 timer:
> 402         if (hdev->idle_timeout > 0)
> 403                 mod_timer(&conn->idle_timer,
> 404                         jiffies + msecs_to_jiffies(hdev->idle_timeout));
> 405 }
> 406 
> 
> If possible, could you explain why this code checks !conn->power_save var.? 
> 
> Without this , if  conn->mode==HCI_CM_SNIFF , we simply exit sniff
> mode,"OCF_EXIT_SNIFF_MODE".
> 
> As far as I understood, whenever conn->mode is HCI_CM_SNIFF conn->power_save
> is 0.
> The reason is that  hci_mode_change_evt() set conn->power_save as "0" when
> conn->mode !=HCI_CM_ACTIVE.
> 
> Consequently we don't need to check that variable.

we do need that variable, because otherwise devices like HID which do
active sniff mode management fall over if we always try to exit sniff
mode only for a few bytes.

Regards

Marcel