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> Johan
