Re: [PATCH v2 3/5] drm/doc: Document DRM_WEDGE_RECOVERY_COLD_RESET recovery method

Mallesh, Koujalagi
2026-03-30T14:02:51Z

Hi Riana,

On 30-03-2026 10:30 am, Tauro, Riana wrote:
>
> On 3/18/2026 12:10 PM, Mallesh Koujalagi wrote:
>> Add documentation for the DRM_WEDGE_RECOVERY_COLD_RESET recovery
>> method introduced for handling power management unit errors. This
>> method is
>> designated for severe errors that compromise core device functionality
>> and are unrecoverable via recovery mechanisms such as driver reload
>> or PCIe
>> bus reset. The documentation clarifies when this recovery method
>> should be
>> used and its implications for userspace applications.
>>
>> v2:
>> - Add several instead of number to avoid update. (Jani)
>>
>> Signed-off-by: Mallesh Koujalagi <mallesh.koujalagi@intel.com>
>> ---
>>   Documentation/gpu/drm-uapi.rst | 73 +++++++++++++++++++++++++++++++++-
>>   1 file changed, 72 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/gpu/drm-uapi.rst
>> b/Documentation/gpu/drm-uapi.rst
>> index d98428a592f1..5b63f1c17b9b 100644
>> --- a/Documentation/gpu/drm-uapi.rst
>> +++ b/Documentation/gpu/drm-uapi.rst
>> @@ -418,7 +418,7 @@ needed.
>>   Recovery
>>   --------
>>   -Current implementation defines four recovery methods, out of
>> which, drivers
>> +Current implementation defines several recovery methods, out of
>> which, drivers
>>   can use any one, multiple or none. Method(s) of choice will be sent
>> in the
>>   uevent environment as ``WEDGED=<method1>[,..,<methodN>]`` in order
>> of less to
>>   more side-effects. See the section `Vendor Specific Recovery`_
>> @@ -435,6 +435,7 @@ following expectations.
>>       rebind          unbind + bind driver
>>       bus-reset       unbind + bus reset/re-enumeration + bind
>>       vendor-specific vendor specific recovery method
>> +    cold-reset      full device cold reset required
>>       unknown         consumer policy
>>       =============== ========================================
>>   @@ -446,6 +447,27 @@ telemetry information (devcoredump, syslog).
>> This is useful because the first
>>   hang is usually the most critical one which can result in
>> consequential hangs or
>>   complete wedging.
>>   +Cold Reset Recovery
>> +-------------------
>> +
>> +The ``WEDGED=cold-reset`` event indicates that the device has
>> encountered
>> +power management unit errors that affect core functionality that
>> cannot be
>
> Power management errors may be only xe usecase.  Keep the
> documentation vendor-agnostic.
> Some vendors may want to use it for a different usecase
>
>> +resolved through recovery mechanisms.
>> +
>> +This recovery method is reserved for power management unit error
>> conditions where the
> Same as above
>
Agree, will rework!

Thanks,

-/Mallesh

> Thanks
> Riana
>
>
>> +device state cannot be restored via:
>> +
>> +- Driver unbind/rebind operations
>> +- PCIe bus reset and re-enumeration
>> +- Device Function Level Reset (FLR)
>> +- Warm device resets
>> +
>> +Such power management unit error state typically persists across all
>> software-based
>> +recovery attempts. Only a complete device power cycle can restore
>> +normal operation.
>> +
>> +Upon receiving a ``WEDGED=cold-reset`` event, userspace should initiate
>> +a full cold reset of the affected device to restore functionality.
>>     Vendor Specific Recovery
>>   ------------------------
>> @@ -524,6 +546,55 @@ Recovery script::
>>       echo -n $DEVICE > $DRIVER/unbind
>>       echo -n $DEVICE > $DRIVER/bind
>>   +Example - cold-reset
>> +--------------------
>> +
>> +Udev rule::
>> +
>> +    SUBSYSTEM=="drm", ENV{WEDGED}=="cold-reset",
>> DEVPATH=="*/drm/card[0-9]",
>> +    RUN+="/path/to/cold-reset.sh $env{DEVPATH}"
>> +
>> +Recovery script::
>> +
>> +    #!/bin/sh
>> +
>> +    [ -z "$1" ] && echo "Usage: $0 <device-path>" && exit 1
>> +
>> +    # Get device
>> +    DEVPATH=$(readlink -f /sys/$1/device 2>/dev/null || readlink -f
>> /sys/$1)
>> +    DEVICE=$(basename $DEVPATH)
>> +
>> +    echo "Cold reset: $DEVICE"
>> +
>> +    # Try slot power reset first
>> +    SLOT=$(find /sys/bus/pci/slots/ -type l 2>/dev/null | while read
>> slot; do
>> +        ADDR=$(cat "$slot" 2>/dev/null)
>> +        [ -n "$ADDR" ] && echo "$DEVICE" | grep -q "^$ADDR" &&
>> basename $(dirname "$slot") && break
>> +    done)
>> +
>> +    if [ -n "$SLOT" ]; then
>> +    echo "Using slot $SLOT"
>> +
>> +    # Unbind driver
>> +    [ -e "/sys/bus/pci/devices/$DEVICE/driver" ] && \
>> +    echo "$DEVICE" > /sys/bus/pci/devices/$DEVICE/driver/unbind
>> 2>/dev/null
>> +
>> +    # Remove device
>> +    echo 1 > /sys/bus/pci/devices/$DEVICE/remove
>> +
>> +    # Power cycle slot
>> +    echo 0 > /sys/bus/pci/slots/$SLOT/power
>> +    sleep 2
>> +    echo 1 > /sys/bus/pci/slots/$SLOT/power
>> +    sleep 1
>> +
>> +    # Rescan
>> +    echo 1 > /sys/bus/pci/rescan
>> +    echo "Done!"
>> +    else
>> +    echo "No slot found"
>> +    fi
>> +
>>   Customization
>>   -------------