The problem, at this point, is that a change this broad must also be tested across all platforms to make sure it's not breaking.
This looks like it was done for a hardware problem. We had a lot of x86 implementations in tree at that time, and they had lots of bugs. On Mon, Oct 4, 2021 at 8:11 AM Julian Stecklina <julian.steckl...@cyberus-technology.de> wrote: > > On Mon, 2021-10-04 at 07:32 -0700, ron minnich wrote: > > that was pre-git but is there any useful comment in git anyway? I only > > have the vaguest memory of why it went in. > > It was introduced in c84c1906b7 and fcd5ace00b3 without explanation. I > particularly don't understand the lapic_write_around and lapic_read_around > functions that pop up. From my perspective, none of this is needed and you can > just use the usual lapic_read and lapic_write functions. > > Julian > > > > > On Mon, Oct 4, 2021 at 7:14 AM Julian Stecklina > > <julian.steckl...@cyberus-technology.de> wrote: > > > > > > Hello, > > > > > > I was looking at the Local APIC code in coreboot and was wondering about > > > `lapic_write_atomic` in src/include/cpu/x86/lapic.h. This uses an atomic > > > XCHG to > > > write to Local APIC registers. I would like to understand why this would > > > be > > > necessary, because none of the OSes I've seen or worked on do anything > > > similar. > > > ALso the Intel SDM discourages acceses that are not plain loads/stores. > > > > > > In the coreboot code, this function seems to exist for a really long time. > > > I've > > > found this from 2004: > > > > > > #ifdef CONFIG_X86_GOOD_APIC > > > # define FORCE_READ_AROUND_WRITE 0 > > > # define lapic_read_around(x) lapic_read(x) > > > # define lapic_write_around(x,y) lapic_write((x),(y)) > > > #else > > > # define FORCE_READ_AROUND_WRITE 1 > > > # define lapic_read_around(x) lapic_read(x) > > > # define lapic_write_around(x,y) lapic_write_atomic((x),(y)) > > > #endif > > > > > > This seems to indicate that using atomic writes was a workaround of some > > > kind. > > > Does anyone know more? > > > > > > Thanks! > > > Julian > > _______________________________________________ coreboot mailing list -- coreboot@coreboot.org To unsubscribe send an email to coreboot-le...@coreboot.org
