On Sat, Sep 17, 2022 at 11:09:44AM +0200, Mateusz Jończyk wrote: > On some platforms, the ACPI _PRT function returns duplicate interrupt > routing entries. Linux uses the first matching entry, but sometimes the > second matching entry contains the correct interrupt vector. > > This happens on a Dell Latitude E6500 laptop with the i2c-i801 Intel > SMBus controller. This controller was nonfunctional unless its interrupt > usage was disabled (using the "disable_features=0x10" module parameter). > > After investigation, it turned out that the driver was using an > incorrect interrupt vector: in lspci output for this device there was: > Interrupt: pin B routed to IRQ 19 > but after running i2cdetect (without using any i2c-i801 module > parameters) the following was logged to dmesg: > > [...] > [ 132.248657] i801_smbus 0000:00:1f.3: Timeout waiting for interrupt! > [ 132.248669] i801_smbus 0000:00:1f.3: Transaction timeout > [ 132.452649] i801_smbus 0000:00:1f.3: Timeout waiting for interrupt! > [ 132.452662] i801_smbus 0000:00:1f.3: Transaction timeout > [ 132.467682] irq 17: nobody cared (try booting with the "irqpoll" option) Drop the timestamps; they add clutter but not useful information. > Existence of duplicate entries in a table returned by the _PRT method > was confirmed by disassembling the ACPI DSTD table. > > Linux used the first matching entry, which was incorrect. In order not > to disrupt existing systems, use the first matching entry unless the > pci=prtlast kernel parameter is used or a Dell Latitude E6500 laptop is > detected. Do we have a reason to believe that in general, using the first matching entry is incorrect? I don't see anything in the ACPI spec (r6.5, sec 6.2.13) that sheds light on this. Presumably this works on Windows, and I doubt Windows would have a platform quirk for this, so I hypothesize that Windows treats _PRT entries as assignments, and the last one rules. Maybe Linux should adopt that rule? Bjorn
