Re: [PATCH 3/3] platform/x86: Intel PMT Crashlog capability driver

From: Hans de Goede
Date: Mon Sep 21 2020 - 10:02:20 EST


On 9/21/20 3:57 PM, Alexander Duyck wrote:
On Mon, Sep 21, 2020 at 6:16 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:


On 9/17/20 11:35 PM, Alexander Duyck wrote:
On Thu, Sep 17, 2020 at 5:12 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:


On 9/15/20 12:35 AM, Alexander Duyck wrote:
On Mon, Sep 14, 2020 at 11:07 AM Alexander Duyck
<alexander.duyck@xxxxxxxxx> wrote:

On Mon, Sep 14, 2020 at 6:42 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:


On 9/11/20 9:45 PM, David E. Box wrote:
From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

Add support for the Intel Platform Monitoring Technology crashlog
interface. This interface provides a few sysfs values to allow for
controlling the crashlog telemetry interface as well as a character driver
to allow for mapping the crashlog memory region so that it can be accessed
after a crashlog has been recorded.

This driver is meant to only support the server version of the crashlog
which is identified as crash_type 1 with a version of zero. Currently no
other types are supported.

Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Signed-off-by: David E. Box <>
.../ABI/testing/sysfs-class-pmt_crashlog | 66 ++
drivers/platform/x86/Kconfig | 10 +
drivers/platform/x86/Makefile | 1 +
drivers/platform/x86/intel_pmt_crashlog.c | 588 ++++++++++++++++++
4 files changed, 665 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-class-pmt_crashlog
create mode 100644 drivers/platform/x86/intel_pmt_crashlog.c

diff --git a/Documentation/ABI/testing/sysfs-class-pmt_crashlog b/Documentation/ABI/testing/sysfs-class-pmt_crashlog
new file mode 100644
index 000000000000..40fb4ff437a6
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-pmt_crashlog
@@ -0,0 +1,66 @@
+What: /sys/class/pmt_crashlog/
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ The pmt_crashlog/ class directory contains information
+ for devices that expose crashlog capabilities using the Intel
+ Platform Monitoring Technology (PTM).
+What: /sys/class/pmt_crashlog/crashlogX
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ The crashlogX directory contains files for configuring an
+ instance of a PMT crashlog device that can perform crash data
+ recoring. Each crashlogX device has an associated
+ /dev/crashlogX device node. This node can be opened and mapped
+ to access the resulting crashlog data. The register layout for
+ the log can be determined from an XML file of specified guid
+ for the parent device.
+What: /sys/class/pmt_crashlog/crashlogX/guid
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ (RO) The guid for this crashlog device. The guid identifies the
+ version of the XML file for the parent device that should be
+ used to determine the register layout.
+What: /sys/class/pmt_crashlog/crashlogX/size
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ (RO) The length of the result buffer in bytes that corresponds
+ to the mapping size for the /dev/crashlogX device node.
+What: /sys/class/pmt_crashlog/crashlogX/offset
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ (RO) The offset of the buffer in bytes that corresponds
+ to the mapping for the /dev/crashlogX device node.
+What: /sys/class/pmt_crashlog/crashlogX/enable
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ (RW) Boolean value controlling if the crashlog functionality
+ is enabled for the /dev/crashlogX device node.
+What: /sys/class/pmt_crashlog/crashlogX/trigger
+Date: September 2020
+KernelVersion: 5.10
+Contact: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
+ (RW) Boolean value controlling the triggering of the
+ /dev/crashlogX device node. When read it provides data on if
+ the crashlog has been triggered. When written to it can be
+ used to either clear the current trigger by writing false, or
+ to trigger a new event if the trigger is not currently set.

Both the pmt_crashlog and the attributes suggest that this is highly
Intel PMT specific. /sys/class/foo interfaces are generally speaking
meant to be generic interfaces.

If this was defining a generic, vendor and implementation agnostic interface for
configuring / accessing crashlogs, then using a class would be fine, but that
is not the case, so I believe that this should not implement / register a class.

Since the devices are instantiated through MFD there already is a
static sysfs-path which can be used to find the device in sysfs:

So you can register the sysfs attributes directly under the platform_device
and then userspace can easily find them, so there really is no need to
use a class here.

I see. So we change the root directory from "/sys/class/pmt_crashlog/"
to "/sys/bus/platform/device/pmt_crashlog" while retaining the same
functionality. That should be workable.

So one issue as I see it is that if we were to change this then we
probably need to to change the telemetry functionality that was
recently accepted

You say that this has been accepted, by I don't see any intel_pmt.c
file here yet: ?

Here is a link to the thread on the first patch set. The last notes I
saw were that it was going to be applied but it looks like that never

as well. The general idea with using the /sys/class/pmt_crashlog/
approach was to keep things consistent with how the pmt_telemetry was
being accessed. So if we change this then we end up with very
different interfaces for the two very similar pieces of functionality.
So ideally we would want to change both telemetry and crashlog to
function the same way.

I agree that the telemetry interface should be changed in a similar way.

Luckily it seems that this is not in Linus' tree yet and I'm also not
seeing it in next yet, e.g. :
does not exist.

So we seem to still have time to also get the telemetry driver userspace API
fixed too.

I see that Andy gave his Reviewed-by for the intel_pmt_telemetry.c code.

Andy, I have some concerns about the userspace API choices made here,
see my earlier review of this patch. Do you agree with my suggestions,
or do you think it would be ok to move forward with the telemetry and
now also the crashlog API each registering their own private class
under /sys/class ?

AFAIK classes are supposed to be generic and not driver-private, so
that seems wrong to me. Also PMC is Intel specific and vendor specific
stuff really does not belong under /sys/class AFAIK ?

Do you have any good examples of anything that has done something
similar? From what I can tell it looks like we need to clean up the
naming to drop the "" for the bus directory names

Assuming there will only be one of each platform-device, then you
can just replace the PLATFORM_DEVID_AUTO param to devm_mfd_add_devices()
with PLATFORM_DEVID_NONE and the will go away.

We will have multiples of each platform device. So for example we can
have multiple OOBMSM in each system and each OOBMSM may have multiple
telemetry regions and maybe one crashlog.

What is a OOBMSM ? Please don't make the person reviewing your patches
do detective work. Only use acronyms if they are something of which
you could reasonably expect any mailinglist reader to know what
they are.

OOBMSM is an acronym for the Out-of-Band Management Services Module.
It is a PCIe function exposed by a device or CPU to provide in-band

So looking at:

What you are saying (I guess) is that both the pmt_pci_probe()
function may run multiple times; and that for a single pmt_pci_probe()
call, pmt_add_dev() may hit the DVSEC_INTEL_ID_TELEMETRY case more then

If I understand either one correct, then indeed we need PLATFORM_DEVID_AUTO.

Which I guess makes using a class for enumeration somewhat sensible.

Correct. In our case there will be multiple instances of each device
being potentially allocated.

But I really do not think we need 2 separate classes, one for
pmt_telemetry and one for pmt_crashlog. Also since this is rather
Intel specific lets at least make that clear in the name.

So how about intel_pmt as class and then register both the telemetry
and the crashlog devs there? (the type can easily be deferred from
the name part before the suffix) ?

Agreed. So we would set it up as an intel_pmt and then in the case of
crashlog we would be adding the binary sysfs for the memory access, a
trigger control, and the enable control. For the telemetry we would
just be adding the binary sysfs for the telemetry access. Do I have
all of that correct?

Yes sounds good.