From mboxrd@z Thu Jan 1 00:00:00 1970 From: f.fainelli@gmail.com (Florian Fainelli) Date: Thu, 08 Jan 2015 07:53:04 -0800 Subject: [RFC] ARM: Make CPU_DCACHE_DISABLE depend on !SMP In-Reply-To: <20150108115219.GS12302@n2100.arm.linux.org.uk> References: <1420683088-1856-1-git-send-email-f.fainelli@gmail.com> <2868984.6iP3luxIAM@wuerfel> <20150108115219.GS12302@n2100.arm.linux.org.uk> Message-ID: <54AEA7E0.5070101@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Le 08/01/2015 03:52, Russell King - ARM Linux a ?crit : > On Thu, Jan 08, 2015 at 09:33:05AM +0100, Arnd Bergmann wrote: >> On Wednesday 07 January 2015 18:11:28 Florian Fainelli wrote: >>> Enabling CPU_DCACHE_DISABLE on a SMP capable system will prevent the >>> kernel from booting because of the following ldrex instruction in >>> arch_spin_lock: >>> >>> (gdb) x/10i $pc >>> => 0xc053cfa8 <_raw_spin_lock+4>: ldrex r3, [r0] >>> 0xc053cfac <_raw_spin_lock+8>: add r2, r3, #65536 ; 0x10000 >>> >>> which is taken by the very first printk call: >>> >>> at /home/fainelli/work/linux/arch/arm/include/asm/spinlock.h:65 >>> fmt=0xc0637650 "\001\066Booting Linux on physical CPU 0x%x\n", args=) >>> at kernel/printk/printk.c:1525 >>> fmt=0xc05370f4 "\024\320\215\342\004\340\235\344\020\320\215\342\036\377/\341\017") at kernel/printk/printk.c:1688 >>> >>> ldrex requires exclusive monitor(s) (local or global) which are no longer >>> working when the Data cache is disabled in CP15 and will just hang the CPU >>> there. >>> >>> Signed-off-by: Florian Fainelli >> >> Acked-by: Arnd Bergmann >> >> We stumbled on this a while back when Kaixu was trying to fix allmodconfig >> builds to run on real hardware, but never submitted it in the end when >> Russell didn't like some of the other parts required for that to work. >> >> This one clearly makes sense independently. > > What about platforms where exclusives to strongly ordered memory do work? Do we have a comprehensive list of these platforms? > > I seem to remember patches from Tony for the pstore/ram_core driver to > allow it to map stuff strongly ordered, and use exclusives on it. Would you have links to these patches handy? -- Florian