[ Adding some more people on CC. ] On Tue, Apr 24, 2018 at 04:29:53PM +0800, Shrirang Bagul wrote: > 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 [1]. > > 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. > > In kernels before the introduction of 'Serial Device Bus (serdev)' > subsystem, these devices were accessible using /dev/ttySx nodes. But, > kernels since 4.15 can no longer do so. > > 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. > > This patch implements a new driver which binds to the ACPI serdev slaves > enumerated by the serdev port controller and exposes /dev/ttyHSx device > nodes which the userspace applications can use. Otherwise, upgrades to 4.15 > or higher kernels would certainly render these devices unusable. > > Considering serdev is new and evolving, this is one approach to solving > the problem at hand. An obvious drawback is the change in the tty device > node name from ttySx => ttyHSx, which means userspace applications have to > be modified (I know that this is strongly discouraged). For the same > reason, I am submitting these patches as RFC. > > If there are other/better ways of solving this or improving on the > proposed solution, that will be most helpful. Yeah, I don't think this is the right solution to this problem. It seems we need to blacklist (or maybe even use whitelists) ACPI-ids until there are drivers for the slave devices that would otherwise be claimed by serdev. > This patch is based on: > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v4.17-rc2 > > [1] Enabling Multi-COM Port for Microsoft Windows OS 8.1 & 10 / IoT Core [Sec. 4.1] > (https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/enabling-multi-com-port-white-paper.pdf) Thanks, Johan -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
