Subject: [RFC] ARM: Make CPU_DCACHE_DISABLE depend on !SMP

From: [email-masked] (Florian Fainelli)
Date: Thu, 08 Jan 2015 07:53:04 -0800

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=<incomplete type>)
>>>     at kernel/printk/printk.c:1525
>>>     fmt=0xc05370f4 <printk+52> "\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 <[email-masked]>
>>
>> Acked-by: Arnd Bergmann <[email-masked]>
>>
>> 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