Re: bcm2711_thermal: Kernel panic - not syncing: Asynchronous SError Interrupt

From: Florian Fainelli
Date: Mon Aug 01 2022 - 11:34:28 EST



On 7/28/2022 2:06 AM, Juerg Haefliger wrote:
On Wed, 27 Jul 2022 14:51:24 -0700
Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:

On 7/27/22 01:05, Juerg Haefliger wrote:
On Wed, 10 Feb 2021 14:59:45 -0800
Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
On 2/10/2021 8:55 AM, Nicolas Saenz Julienne wrote:
Hi Robin,

On Wed, 2021-02-10 at 16:25 +0000, Robin Murphy wrote:
On 2021-02-10 13:15, Nicolas Saenz Julienne wrote:
[ Add Robin, Catalin and Florian in case they want to chime in ]

Hi Juerg, thanks for the report!

On Wed, 2021-02-10 at 11:48 +0100, Juerg Haefliger wrote:
Trying to dump the BCM2711 registers kills the kernel:

# cat /sys/kernel/debug/regmap/dummy-avs-monitor\@fd5d2000/range
0-efc
# cat /sys/kernel/debug/regmap/dummy-avs-monitor\@fd5d2000/registers

[ 62.857661] SError Interrupt on CPU1, code 0xbf000002 -- SError

So ESR's IDS (bit 24) is set, which means it's an 'Implementation Defined
SError,' hence IIUC the rest of the error code is meaningless to anyone outside
of Broadcom/RPi.

It's imp-def from the architecture's PoV, but the implementation in this
case is Cortex-A72, where 0x000002 means an attributable, containable
Slave Error:

https://developer.arm.com/documentation/100095/0003/system-control/aarch64-register-descriptions/exception-syndrome-register--el1-and-el3?lang=en

In other words, the thing at the other end of an interconnect
transaction said "no" :)

(The fact that Cortex-A72 gets too far ahead of itself to take it as a
synchronous external abort is a mild annoyance, but hey...)

Thanks for both your clarifications! Reading arm documentation is a skill on
its own.

Yes it is.
The regmap is created through the following syscon device:

avs_monitor: avs-monitor@7d5d2000 {
compatible = "brcm,bcm2711-avs-monitor",
"syscon", "simple-mfd";
reg = <0x7d5d2000 0xf00>;

thermal: thermal {
compatible = "brcm,bcm2711-thermal";
#thermal-sensor-cells = <0>;
};
};

I've done some tests with devmem, and the whole <0x7d5d2000 0xf00> range is
full of addresses that trigger this same error. Also note that as per Florian's
comments[1]: "AVS_RO_REGISTERS_0: 0x7d5d2200 - 0x7d5d22e3." But from what I can
tell, at least 0x7d5d22b0 seems to be faulty too.

Any ideas/comments? My guess is that those addresses are marked somehow as
secure, and only for VC4 to access (VC4 is RPi4's co-processor). Ultimately,
the solution is to narrow the register range exposed by avs-monitor to whatever
bcm2711-thermal needs (which is ATM a single 32bit register).

When a peripheral decodes a region of address space, nobody says it has
to accept accesses to *every* address in that space; registers may be
sparsely populated, and although some devices might be "nice" and make
unused areas behave as RAZ/WI, others may throw slave errors if you poke
at the wrong places. As you note, in a TrustZone-aware device some
registers may only exist in one or other of the Secure/Non-Secure
address spaces.

Even when there is a defined register at a given address, it still
doesn't necessarily accept all possible types of access; it wouldn't be
particularly friendly, but a device *could* have, say, some registers
that support 32-bit accesses and others that only support 16-bit
accesses, and thus throw slave errors if you do the wrong thing in the
wrong place.

It really all depends on the device itself.

All in all, assuming there is no special device quirk to apply, the feeling I'm
getting is to just let the error be. As you hint, firmware has no blame here,
and debugfs is a 'best effort, zero guarantees' interface after all.

We should probably fill a regmap_access_table to deny reading registers
for which there is no address decoding and possibly another one to deny
writing to the read-only registers.


Below is a patch that adds a read access table but it seems wrong to include
'internal.h' and add the table in the thermal driver. Shouldn't this happen
in a higher layer, somehow between syscon and the thermal node?

What is the purpose of doing doing this though that cannot already be done using devmem/devmem2 if the point is explore the address space?

The goal is to prevent a kernel crash when doing
$ cat /sys/kernel/debug/regmap/dummy-avs-monitor\@fd5d2000/registers

Fair enough, but that really does not scale across drivers nor across power management decisions being made to various drivers.

The thermal sensor is unlikely to ever be clock gated by the time Linux runs, but if you were to do the same thing for any other type of peripheral, chances are the same outcome would be produced.

So this really begs the question as to how to address this globally short of disabling regmap debugfs support which is likely what is happening in a production environment anyway.
--
Florian