4.4-stable review patch. If anyone has any objections, please let me know.
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From: Macpaul Lin macpaul.lin@mediatek.com
commit eafb27fa5283599ce6c5492ea18cf636a28222bb upstream.
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@mediatek.com Cc: stable@vger.kernel.org Reviewed-by: Johan Hovold johan@kernel.org Acked-by: Oliver Neukum oneukum@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/usb/class/cdc-acm.c | 10 ++++++++++ drivers/usb/class/cdc-acm.h | 1 + 2 files changed, 11 insertions(+)
--- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -507,6 +507,13 @@ static int acm_tty_install(struct tty_dr if (retval) goto error_init_termios;
+ /* + * Suppress initial echoing for some devices which might send data + * immediately after acm driver has been installed. + */ + if (acm->quirks & DISABLE_ECHO) + tty->termios.c_lflag &= ~ECHO; + tty->driver_data = acm;
return 0; @@ -1677,6 +1684,9 @@ static const struct usb_device_id acm_id { USB_DEVICE(0x0e8d, 0x0003), /* FIREFLY, MediaTek Inc; andrey.arapov@gmail.com */ .driver_info = NO_UNION_NORMAL, /* has no union descriptor */ }, + { USB_DEVICE(0x0e8d, 0x2000), /* MediaTek Inc Preloader */ + .driver_info = DISABLE_ECHO, /* DISABLE ECHO in termios flag */ + }, { USB_DEVICE(0x0e8d, 0x3329), /* MediaTek Inc GPS */ .driver_info = NO_UNION_NORMAL, /* has no union descriptor */ }, --- a/drivers/usb/class/cdc-acm.h +++ b/drivers/usb/class/cdc-acm.h @@ -134,3 +134,4 @@ struct acm { #define QUIRK_CONTROL_LINE_STATE BIT(6) #define CLEAR_HALT_CONDITIONS BIT(7) #define SEND_ZERO_PACKET BIT(8) +#define DISABLE_ECHO BIT(9)