arm/183740: mutex on some arm hardware requires dcache enabled

[John Wehle]

>Number:         183740
>Category:       arm
>Synopsis:       mutex on some arm hardware requires dcache enabled
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-arm
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Nov 07 07:10:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     John Wehle
>Release:        FreeBSD svn 257205
>Organization:
Personal
>Environment:
Not Yet
>Description:
In my spare time I'm working on bringing FreeBSD up on amlogic based
arm processors.  While working through various bootstrap issues I got
to the point where initarm calls pmap_bootstrap only to have it splat.

What happens is pmap_bootstrap calls pmap_extract which does PMAP_LOCK(pmap).
This trys to acquire a mutex which invokes atomics that use ldrex / strex.

The ARM documentation at:

  http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0464d/CHDIBJGE.html

notes that the L1 memory system has an internal exclusive monitor which
handles ldrex / strex accesses.

The README at:

  https://github.com/dwelch67/raspberrypi/tree/master/extest

has a nice write up which explains some of the wrinkles regarding hardware
and ldrex / strex.

The attached patch enables the dcache and suffices to get me through
initarm into mi_startup (I'm not to a console login yet ... however
I'm significantly further along).

-- John

>How-To-Repeat:

>Fix:
Enable the dcache prior to using a mutex.

Patch attached with submission follows:

--- sys/arm/arm/machdep.c.ORIGINAL	2013-10-27 01:15:39.000000000 -0400
+++ sys/arm/arm/machdep.c	2013-11-07 01:43:01.000000000 -0500
@@ -1481,6 +1483,12 @@ initarm(struct arm_boot_params *abp)
 	 */
 	cpu_idcache_wbinv_all();
 
+	/*
+	 * Atomics invoked by mutex use ldrex / strex which on some
+	 * hardware requires the L1 cache.
+	 */
+	cpu_control(CPU_CONTROL_DC_ENABLE, CPU_CONTROL_DC_ENABLE);
+
 	/* Set stack for exception handlers */
 	data_abort_handler_address = (u_int)data_abort_handler;
 	prefetch_abort_handler_address = (u_int)prefetch_abort_handler;


>Release-Note:
>Audit-Trail:
>Unformatted: