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

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Date:	Thu, 14 Apr 2016 06:28:33 +0200
From:	Juergen Gross <jgross@...e.com>
To:	"Luis R. Rodriguez" <mcgrof@...nel.org>, bp@...en8.de,
	hpa@...or.com, tglx@...utronix.de, mingo@...hat.com,
	rusty@...tcorp.com.au
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, luto@...capital.net,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	konrad.wilk@...cle.com, xen-devel@...ts.xensource.com,
	lguest@...ts.ozlabs.org, andriy.shevchenko@...ux.intel.com,
	jlee@...e.com, glin@...e.com, matt@...eblueprint.co.uk,
	andrew.cooper3@...rix.com, rjw@...ysocki.net, lenb@...nel.org,
	robert.moore@...el.com, lv.zheng@...el.com, toshi.kani@...com,
	linux-acpi@...r.kernel.org, kozerkov@...allels.com,
	josh@...htriplett.org, bigeasy@...utronix.de, ffainelli@...ebox.fr,
	george.dunlap@...rix.com, julien.grall@...aro.org,
	mbizon@...ebox.fr, tiwai@...e.de
Subject: Re: [PATCH v6 04/16] x86/rtc: replace paravirt rtc check with
 platform legacy quirk

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@...nel.org>
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen