QEMU

  1. Bug #1918917
  2. Comment #3

Comment 3 for bug 1918917

Revision history for this message
Arnd Bergmann (arnd-arndb) wrote : Re: synchronous about on accessing unused I/O ports on aarch64

That seems correct, and could probably be improved. In this case, I know that _outb() only writes within the PCI PIO virtual address between fffffbfffe800000 and fffffbffff800000, which according to the boot log (https://gist.githubusercontent.com/dvyukov/084890d9b4aa7cd54f468e652a9b5881/raw/54c12248ff6a4885ba6c530d56b3adad59bc6187/gistfile1.txt) was mapped to qemu's PCI IO space, using DEVICE_nGnRnE attributes (PIO space unlike any other MMIO in the kernel uses 'nE'):

[ 3.973419][ T1] pci-host-generic 4010000000.pcie: host bridge /pcie@10000000 ranges:
[ 3.974309][ T1] pci-host-generic 4010000000.pcie: IO 0x003eff0000..0x003effffff -> 0x0000000000
[ 3.975021][ T1] pci-host-generic 4010000000.pcie: MEM 0x0010000000..0x003efeffff -> 0x0010000000

So physical address 0x003eff0000 corresponds to virtual address fffffbfffe800000, which corresponds to logical PIO port number 0. The serial port in the kernel was probed at port number 0, so the driver attempts to write to the 8250 compatible UART_IER at address fffffbfffe800001, which is in register x19.