Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] x86/i8259: Work around buggy legacy PIC | Date | Fri, 14 May 2021 13:13:19 +0000 |
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From: Thomas Gleixner > Sent: 14 May 2021 14:02 > > David, > > On Thu, May 13 2021 at 10:36, David Laight wrote: > > >> -----Original Message----- > >> From: Maximilian Luz <luzmaximilian@gmail.com> > > can you please fix your mail client and spare us the useless header > duplication in the reply?
I have to delete them by hand - must have forgotten, I can't fix outlook :-)
> > It is also worth noting that the probe code is spectacularly crap. > > It writes 0xff and then checks that 0xff is read back. > > Almost anything (including a failed PCIe read to the ISA bridge) > > will return 0xff and make the test pass. > > unsigned char probe_val = ~(1 << PIC_CASCADE_IR); > > outb(probe_val, PIC_MASTER_IMR); > new_val = inb(PIC_MASTER_IMR); > > How is that writing 0xFF?
Sorry I misread the code and diagnostic output.
In any case writing a value and expecting the same value back isn't exactly a high-quality probe.
David
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