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 <macpaul.lin@xxxxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > --- > > 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 <johan@xxxxxxxxxx> Acked-by: Oliver Neukum <oneukum@xxxxxxxx>
