Re: [PATCH v6 04/16] x86/rtc: replace paravirt rtc check with platform legacy quirk

[Juergen Gross]

On 14/04/16 02:04, Luis R. Rodriguez wrote:
> We have 4 types of x86 platforms that disable RTC:
> 
>   * Intel MID
>   * Lguest - uses paravirt
>   * Xen dom-U - uses paravirt
>   * x86 on legacy systems annotated with an ACPI legacy flag
> 
> We can consolidate all of these into a platform specific legacy
> quirk set early in boot through i386_start_kernel() and through
> x86_64_start_reservations(). This deals with the RTC quirks which
> we can rely on through the hardware subarch, the ACPI check can
> be dealt with separately.
> 
> For Xen things are bit more complex given that the @X86_SUBARCH_XEN
> x86_hardware_subarch is shared on for Xen which uses the PV path for
> both domU and dom0. Since the semantics for differentiating between
> the two are Xen specific we provide a platform helper to help override
> default legacy features -- x86_platform.set_legacy_features(). Use
> of this helper is highly discouraged, its only purpose should be
> to account for the lack of semantics available within your given
> x86_hardware_subarch.
> 
> As per 0-day, this bumps the vmlinux size using i386-tinyconfig as
> follows:
> 
> TOTAL   TEXT   init.text    x86_early_init_platform_quirks()
> +70     +62    +62          +43
> 
> Only 8 bytes overhead total, as the main increase in size is
> all removed via __init.
> 
> v4: split the subarch check from the ACPI check, clarify
>     on the ACPI change commit log why ordering works
> v5: add x86_platform.set_legacy_features() to account for dom0,
>     add also size impact on vmlinux as per 0-day report
> v6: Use __init on xen_dom0_set_legacy_features()
> 
> Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen