Re: [PATCH v4 3/4] drm/doc: Document DRM_WEDGE_RECOVERY_COLD_RESET recovery method

["Mallesh, Koujalagi" <mallesh.koujalagi@intel.com>]

On 21-04-2026 02:00 pm, Raag Jadav wrote:
> On Mon, Apr 13, 2026 at 07:00:17PM +0530, Mallesh Koujalagi wrote:
>> When ``WEDGED=cold-reset`` is sent, it indicates a non-recoverable
> This looks like "cold-reset" should be able to recover it, so is it
> really non-recoverable? ;)
I'll revert it as per last rev.
>> device error, only a full power cycle can restore the device.
>>
>> v2:
>> - Add several instead of number to avoid update. (Jani)
>>
>> v3:
>> - Update document with generic scenario. (Riana)
>> - Consistent with terminology. (Raag)
>> - Remove already covered information.
>>
>> v4:
>> - Update doc. (Raag/Riana)
>> - Change commit message. (Raag)
>>
>> Signed-off-by: Mallesh Koujalagi <mallesh.koujalagi@intel.com>
>> ---
>>   Documentation/gpu/drm-uapi.rst | 60 +++++++++++++++++++++++++++++++++-
>>   1 file changed, 59 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
>> index 579e87cb9ff7..0b87c8ed760d 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      unbind + remove device + slot power cycle + rescan
> Do you need to unbind if you're already removing the device?
Yes, you are right, when we remove the device unbind is not required.
>
>>       unknown         consumer policy
>>       =============== ========================================
>>   
>> @@ -447,6 +448,14 @@ debug purpose in order to root cause the hang. 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
>> +-------------------
>> +
>> +When ``WEDGED=cold-reset`` is sent, it indicates a non-recoverable device error,
>> +only a full power cycle can restore the device.
> This was phrased much better in last rev, not sure why changed?
I'll revert it as per last rev.
>
>> +This method is used by devices that are plugged directly into the PCIe slot.
> ... which supports removing the power.
>
>>   Vendor Specific Recovery
>>   ------------------------
>>   
>> @@ -524,6 +533,55 @@ 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)
> This looks like too much is happening here, can we try to simplify a bit?
Sure
>
>> +    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
> Is this really needed?

It's nor required. I'll remove those lines.

Thanks,

-/Mallesh

>
> Raag
>
>> +	# 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
>>   -------------
>>   
>> -- 
>> 2.34.1
>>