From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:55988 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725440AbeLTP33 (ORCPT ); Thu, 20 Dec 2018 10:29:29 -0500 Message-ID: <1545319724.5084.3.camel@suse.com> Subject: Re: [PATCH v7] cdc-acm: fix abnormal DATA RX issue for Mediatek Preloader. From: Oliver Neukum To: Johan Hovold , Macpaul Lin Cc: Andrey Arapov , Lars Melin , Greg Kroah-Hartman , Mediatek WSD Upstream , linux-usb@vger.kernel.org, stable@vger.kernel.org Date: Thu, 20 Dec 2018 16:28:44 +0100 In-Reply-To: <20181219090008.GR20658@localhost> References: <1544671676-23912-1-git-send-email-macpaul.lin@mediatek.com> <1545192663-5721-1-git-send-email-macpaul.lin@mediatek.com> <20181219090008.GR20658@localhost> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On Mi, 2018-12-19 at 10:00 +0100, Johan Hovold wrote: > On Wed, Dec 19, 2018 at 12:11:03PM +0800, Macpaul Lin wrote: > > Mediatek Preloader is a proprietary embedded boot loader for loading > > Little Kernel and Linux into device DRAM. > > > > This boot loader also handle firmware update. Mediatek Preloader will be > > enumerated as a virtual COM port when the device is connected to Windows > > or Linux OS via CDC-ACM class driver. When the USB enumeration has been > > done, Mediatek Preloader will send out handshake command "READY" to PC > > actively instead of waiting command from the download tool. > > > > Since Linux 4.12, the commit "tty: reset termios state on device > > registration" (93857edd9829e144acb6c7e72d593f6e01aead66) causes Mediatek > > Preloader receiving some abnoraml command like "READYXX" as it sent. > > This will be recognized as an incorrect response. The behavior change > > also causes the download handshake fail. This change only affects > > subsequent connects if the reconnected device happens to get the same minor > > number. > > > > By disabling the ECHO termios flag could avoid this problem. However, it > > cannot be done by user space configuration when download tool open > > /dev/ttyACM0. This is because the device running Mediatek Preloader will > > send handshake command "READY" immediately once the CDC-ACM driver is > > ready. > > > > This patch wants to fix above problem by introducing "DISABLE_ECHO" > > property in driver_info. When Mediatek Preloader is connected, the > > CDC-ACM driver could disable ECHO flag in termios to avoid the problem. > > > > Signed-off-by: Macpaul Lin > > Cc: stable@vger.kernel.org > > --- > > Changes for v2: > > - Move quirks testing of DISABLE_ECHO flag into acm_tty_install(). > > - Change quirks testing into bitwise comparison. > > Changes for v3: > > - Replace quirks testing from init_termios to tty->termios. > > - Remove parenthesis for ECHO flag. > > Changes for v4: > > - Drop quirks varible to simplify the patch. > > - Move termios operation right after the driver_data has been installed. > > - Write general style comment for suppressing initial echoing. > > Changes for v5: > > - Fix: termios operation right abover the driver_data has been installed. > > - Update commit comment about this patch affects the reconnected device > > which get the same minor numbers. > > Changes for v6: > > - Update VID/PID:0x0e8d/0x0003 as Mediatek Inc BROM. > > - Update VID/PID:0x0e8d/0x2000 as Mediatek Inc Preloader. > > Changes for v7: > > - Keep VID/PID:0x0e8d/0x0003 unchanged because of 2 different UNION > > descriptor implementated in Mediatek Inc BROM (MT6589/MT6765). > > Reviewed-by: Johan Hovold Acked-by: Oliver Neukum