Keith, Eric, When charging Dell E5420 laptops, I see the Sandy Bridge South Display Engine port C hotplug interrupt fire consistently at around 20Hz. Each scan on the connectors results in ~100ms hold time for the mode_config mutex which blocks eg the cursor set ioctl (due to the I2C read timeouts across the connectors), resulting in terrible GUI interactivity. Notably, when only using battery or only using AC, the port C interrupts don't fire. It feels like the platform is using South Display Port C for GPIO/I2C; setting the port C pulse duration from 2ms to 100ms doesn't change the behaviour. I'll dump off the GPIO settings, but what else is good to debug this? Also, have you come across this kind of pattern before, eg a platform using these GPIO ports for the something (in this case, feels like the EC/battery)? Judging by the lack of a quirks, I'd say not. Perhaps also I should dump off the SDE port C IIR mask register before we reset it, in case the BIOS intentionally masks out port C hotplug events. Thanks, ?Daniel -- Daniel J Blueman
