linux-kernel - Re: [PATCH] arm64: Kconfig.platforms: fix warning unmet direct dependencies

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Date:   Wed, 30 Jan 2019 09:43:21 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     will.deacon@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Kconfig.platforms: fix warning unmet direct
 dependencies

On 2019-01-25 16:57, Lucas Stach wrote:
> Am Freitag, den 25.01.2019, 14:32 +0000 schrieb Catalin Marinas:
> > On Tue, Jan 15, 2019 at 08:18:39PM +0100, Anders Roxell wrote:
> > > When ARCH_MXC get enabled, ARM64_ERRATUM_845719 will be selected and
> > > this warning will happen when COMPAT isn't set.
> > > 
> > > WARNING: unmet direct dependencies detected for ARM64_ERRATUM_845719
> > >   Depends on [n]: COMPAT [=n]
> > >   Selected by [y]:
> > >   - ARCH_MXC [=y]
> > > 
> > > Rework to add 'if COMPAT' before ARM64_ERRATUM_845719 gets selected,
> > > since ARM64_ERRATUM_845719 depends on COMPAT.
> > > 
> > > > > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> > > ---
> > >  arch/arm64/Kconfig.platforms | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
> > > index 251ecf34cb02..d4faca775d9c 100644
> > > --- a/arch/arm64/Kconfig.platforms
> > > +++ b/arch/arm64/Kconfig.platforms
> > > @@ -145,7 +145,7 @@ config ARCH_MVEBU
> > >  config ARCH_MXC
> > > > >  	bool "ARMv8 based NXP i.MX SoC family"
> > > > >  	select ARM64_ERRATUM_843419
> > > > > -	select ARM64_ERRATUM_845719
> > > > > +	select ARM64_ERRATUM_845719 if COMPAT
> > > > >  	help
> > > > >  	  This enables support for the ARMv8 based SoCs in the
> > >  	  NXP i.MX family.
> > 
> > Actually, do we need to select the errata workarounds explicitly? That
> > seems to be the only case where we do it (commit 930507c18304, "arm64:
> > add basic Kconfig symbols for i.MX8"). They are default y, so we
> > shouldn't need to force them on.
> 
> This is based on past experience. We've had a lot of cases were people
> did not enable the necessary CPU errata workaround, which then usually
> lead to very hard to debug system failures. It is on our list of things
> to look out for now, but I would feel much better if there is just no
> chance for a user to misconfigure the kernel in this way.
> 

Would a better approach be to remove the 'depends on COMPAT' in the
Kconfig and move it into the src files instead see below.

Cheers,
Anders


diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index d9ab8ff3f7e5..04b11806e2d7 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -430,7 +430,6 @@ config ARM64_ERRATUM_834220
 
 config ARM64_ERRATUM_845719
 	bool "Cortex-A53: 845719: a load might read incorrect data"
-	depends on COMPAT
 	default y
 	help
 	  This option adds an alternative code sequence to work around ARM
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 9950bb0cbd52..43b14a5fc8c1 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -641,7 +641,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		MIDR_FIXED(0x4, BIT(8)),
 	},
 #endif
-#ifdef CONFIG_ARM64_ERRATUM_845719
+#if defined(CONFIG_ARM64_ERRATUM_845719) && defined(CONFIG_COMPAT)
 	{
 	/* Cortex-A53 r0p[01234] */
 		.desc = "ARM erratum 845719",
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 0ec0c46b2c0c..e2be37ee5615 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -311,7 +311,7 @@ alternative_else_nop_endif
 	tst	x22, #PSR_MODE32_BIT		// native task?
 	b.eq	3f
 
-#ifdef CONFIG_ARM64_ERRATUM_845719
+#if defined(CONFIG_ARM64_ERRATUM_845719) && defined(CONFIG_COMPAT)
 alternative_if ARM64_WORKAROUND_845719
 #ifdef CONFIG_PID_IN_CONTEXTIDR
 	mrs	x29, contextidr_el1