[U-Boot] [PATCH v3 1/2] x86: Add efi runtime reset

[Bin Meng <bmeng.cn@gmail.com>]

On Thu, Jan 31, 2019 at 9:24 AM Simon Glass <sjg@chromium.org> wrote:
>
> Hi,
>
> On Wed, 30 Jan 2019 at 12:03, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >
> > On 1/30/19 11:46 AM, Alexander Graf wrote:
> > > Our selftest will soon test the actual runtime reset function rather than
> > > the boot time one. For this, we need to ensure that the runtime version
> > > actually succeeds on x86 to keep our travis tests work.
> > >
> > > So this patch implements an x86 runtime reset function. It is missing
> > > shutdown functionality today, but OSs usually implement that via ACPI
> > > and this function does more than the stub from before, so it's at least
> > > an improvement.
> > >
> > > Eventually we will want to have full DM functionality in runtime services.
> > > But this fixes a travis failure and doesn't clutter the code too heavily, so
> > > we should pull it in without the amazing new RTS DM framework.
> > >
> > > Signed-off-by: Alexander Graf <agraf@suse.de>
> > >
> > > ---
> > >
> > > v2 -> v3:
> > >
> > >   - support EFI_RESET_PLATFORM_SPECIFIC
> > >   - reuse existing x86_sysreset_request() function
> >
> > The v2->v3 update does not answer the question if the reset is correctly
> > implemented. We would not want to call a function we do not trust.
> >
> > @Simon, Bin:
> > x86_sysreset_request() loosely resembles BOOT_CF9_SAFE in
> > native_machine_emergency_restart() in Linux arch/x86/kernel/reboot.c
> > which is tried before using the keyboard controller as last resort.
> >
> > u8 reboot_code = reboot_mode == REBOOT_WARM ?  0x06 : 0x0E;
> > u8 cf9 = inb(0xcf9) & ~reboot_code;
> > outb(cf9|2, 0xcf9); /* Request hard reset */
> > udelay(50);
> > /* Actually do the reset */
> > outb(cf9|reboot_code, 0xcf9);
> > udelay(50);
> >
> > So the Kernel first switches bit 2 off and bit 1 on, waits, and then
> > switches bit 2 on, cf.
> > http://smackerelofopinion.blogspot.com/2011/02/resetting-pc-using-reset-control.html
> >
> > Shouldn't we do it the same way as the Kernel does it?
>
> I suspect so, but Bin is the expert.
>

What U-Boot does is essentially the same as Linux but a simplified
version, because bit 2 is 0 any way. If it were 0, the system should
have been reset already then there is no chance to execute the reset
sequence at all.

> As to this patch, it perpetuates the current EFI run-time approach in
> U-Boot so I'm not sure this is the right path.
>

Regards,
Bin