Hi,
I observed that touching MMIO regions of Tegra devices with its
corresponding clock gate deactivated immediately freezes the whole
system. No kernel panic, nothing.
I tested this behavior with a small kernel module, find it attached. A
few seconds after loading this module, the whole device freezes. Tested
this on a TK1 and TX1.
What is the actual expected behavior on ARM(64) when touching ungated
MMIO regions? Is it specified somewhere?
Why do I actually want to do that?
We're working on the Jailhouse hypervisor that partitions hardware to
isolated partitions, called cells. Devices (e.g. MMIO regions) are
assigned to those cells. A cell might do whatever it wants within its
scope. The hypervisor traps on access violations and will stop that cell.
Touching ungated MMIO regions isn't a violation, but it will hang up the
whole system.
Best
Ralf
---
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <asm/io.h>
MODULE_DESCRIPTION("foobar");
MODULE_LICENSE("GPL");
static int __init mod_init(void)
{
/* try 0x70006200 for UARTD
* or 0x7000c000 for I2C-0.
Make sure those devices are 'disabled' in your DT.
*/
unsigned long phys = 0x70006200;
volatile unsigned int *mmio = ioremap(phys, 0x40);
*mmio = 0xdeadbeef;
iounmap(mmio);
return 0;
}
static void __exit mod_exit(void)
{
}
module_init(mod_init);
module_exit(mod_exit);
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