On Tue, Apr 24, 2018 at 11:16:38PM +0200, Hans de Goede wrote: > Hi, > > On 24-04-18 19:18, Johan Hovold wrote: > > [ 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. > > FWIW I've been using this patch for a while for realtek UART attached bluetooth: > https://github.com/jwrdegoede/linux-sunxi/commit/bc904e3703940600ca66c65fcdb0a8cb01dff55d > which is a gross hack. > > If we're going to do a whitelist for this, it better support some sort of > wildcards as there are a LOT of BCM2E?? devices which need to be on the > whitelist. I think a blacklist would actually be better though, this also > documents which devices are lacking a proper kernel (where applicable). Yeah, you guys know the ACPI space better than I do. I just fear that if we go with the blacklist approach, we'll be playing a whack-a-mole with this for a long time when people start upgrading there systems to 4.15 and discover that their serial ports are gone. Since this would qualify as a severe regression, me may need to consider adding a serdev whitelist for every ACPI id we add to a serdev driver instead. 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
