** Changed in: linux (Ubuntu Bionic)
       Status: Incomplete => Confirmed

** Changed in: linux (Ubuntu Bionic)
   Importance: Undecided => High

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

** Changed in: linux (Ubuntu)
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/1864147

Title:
  [bionic]  Support Intel Atom (Baytrail-I) HS-UART serdev slaves over
  tty

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Bionic:
  Confirmed

Bug description:
  [SRU Justification]

  [Impact]
  Support Intel Atom (Baytrail-I) HS-UART serdev slaves over tty

  On systems using Intel Atom (Baytrail-I) SoC's, slave devices connected on
  HSUART1/2 ports are described by the ACPI BIOS as virtual hardware using
  HID's INT3511/INT3512.

  As a consequence, HW manufacturers have complete freedom to install any
  devices on-board as long as they can be accessed over serial tty
  interface. Once such device is Dell Edge 3002 IoT Gateway which sports
  ZigBee & GPS devices on the HS-UART ports 1 & 2 respectively.

  Post 4.15, with CONFIG_SERIAL_DEV_BUS=y, serdev port controller driver
  handles the enumeration for the slaves connected on these ports. Also,
  /dev/ttySx device nodes for these ports are no longer exposed to the
  userspace.

  [Fixes]
  This patchset allows the skipped virtual UART's with ACPI HID's mentioned
  above to be enumerated as ttyHSx port.

  [Regression Potential]
  Low. This driver binds only to Intel Atom E38XX (Baytrail-I) virtual serial
  ports on the Dell Edge 300x GW. These updates are being carried in the
  linux-oem (4.15.y) kernel for more than 2 years without any regressions.

  [Note]
  This driver has been submitted upstream and is under review. This issue has
  been identified as a regression in 4.15 and multiple solutions are being
  explored. Meanwhile, to support customer and maintain release schedule,
  this driver needs to be in Ubuntu 4.15 based kernels.
  More info:
  https://marc.info/?t=152455871600007&r=1&w=2

  linux-oem buglink: http://bugs.launchpad.net/bugs/1690362

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