linux-kernel - Re: [PATCH v8 1/3] powerpc: Detect the presence of big-cores via "ibm,thread-groups"

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Date:   Fri, 21 Sep 2018 22:47:40 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Michael Neuling <mikey@...ling.org>
Cc:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Murilo Opsfelder Araujo <muriloo@...ux.ibm.com>,
        Anton Blanchard <anton@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/3] powerpc: Detect the presence of big-cores via
 "ibm,thread-groups"

Hello Michael,

On Fri, Sep 21, 2018 at 01:02:45PM +1000, Michael Neuling wrote:
> This doesn't compile for me with:
> 
> arch/powerpc/kernel/smp.c: In function ‘smp_prepare_cpus’:
> arch/powerpc/kernel/smp.c:812:23: error: ‘tg.threads_per_group’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>   struct thread_groups tg;
>                        ^
> arch/powerpc/kernel/smp.c:812:23: error: ‘tg.nr_groups’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> cc1: all warnings being treated as errors
> /home/mikey/src/linux-ozlabs/scripts/Makefile.build:305: recipe for target 'arch/powerpc/kernel/smp.o' failed
>

I couldn't get this error with gcc 4.8.5 and 8.1.1 with
pseries_defconfig and powernv_defconfig with CONFIG_PPC_WERROR=y.

Does the following the following delta patch make it work?

-----------------------------X8----------------------------------

>From 6699ce20573dddd0d3d45ea79015751880740e9b Mon Sep 17 00:00:00 2001
From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Date: Fri, 21 Sep 2018 22:43:05 +0530
Subject: [PATCH] powerpc/smp: Initialize thread_groups local variable

Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/smp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 5cdcf44..356751e 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -809,8 +809,9 @@ static int init_cpu_l1_cache_map(int cpu)
 
 {
 	struct device_node *dn = of_get_cpu_node(cpu, NULL);
-	struct thread_groups tg;
-
+	struct thread_groups tg = {.property = 0,
+				   .nr_groups = 0,
+				   .threads_per_group = 0};
 	int first_thread = cpu_first_thread_sibling(cpu);
 	int i, cpu_group_start = -1, err = 0;
 
-- 
1.9.4