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

[Heinrich Schuchardt]

On 1/31/19 8:31 AM, Bin Meng wrote:
> On Thu, Jan 31, 2019 at 3:30 PM Bin Meng <bmeng.cn at gmail.com> wrote:
>>
>> On Thu, Jan 31, 2019 at 9:24 AM Simon Glass <sjg at chromium.org> wrote:
>>>
>>> Hi,
>>>
>>> On Wed, 30 Jan 2019 at 12:03, Heinrich Schuchardt <xypron.glpk at 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 at 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
> 
> Sorry, a typo: If it were "1"

What happens if we reset a board multiple times?

Best regards

Heinrich

> 
>> 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
>