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

[Raag Jadav <raag.jadav@intel.com>]

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? ;)

> 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?

>      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?

> +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?

> +    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?

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
>