Re: [PATCHv2 8/8] drm/amdgpu: Temporarily enable UALink loopback via module parameter

[Felix Kuehling <felix.kuehling@amd.com>]

On 2026-10-27 15:54, Mukul Joshi wrote:
> Temporarily add the amdgpu.ualink_loopback module parameter to request
> UALink loopback mode for manufacturing testing, until the final
> mechanism for enabling loopback is in place. Loopback is disabled by
> default.
>
> Only amdgpu_ualink_loopback_requested() reads the parameter, so moving
> to the final mechanism only needs to replace it there.
>
> Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>

Acked-by: Felix Kuehling <felix.kuehling@amd.com>

We probably don't want to push this one upstream. It could be for our 
internal branch only until we have the proper detection method in place.

Regards,
   Felix


> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu.h        |  1 +
>   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    | 13 +++++++++++++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c |  5 +++--
>   3 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index 5a32b54b1e9b..b8be093b8a33 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -270,6 +270,7 @@ extern int amdgpu_rebar;
>   extern int amdgpu_wbrf;
>   extern int amdgpu_user_queue;
>   extern int amdgpu_ptl;
> +extern int amdgpu_ualink_loopback;
>   
>   extern uint amdgpu_hdmi_hpd_debounce_delay_ms;
>   
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index 3e5634de077f..e0cf40f86194 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -253,6 +253,7 @@ int amdgpu_rebar = -1; /* auto */
>   int amdgpu_user_queue = -1;
>   uint amdgpu_hdmi_hpd_debounce_delay_ms;
>   int amdgpu_ptl = -1; /* auto */
> +int amdgpu_ualink_loopback;
>   
>   DECLARE_DYNDBG_CLASSMAP(drm_debug_classes, DD_CLASS_TYPE_DISJOINT_BITS, 0,
>   			"DRM_UT_CORE",
> @@ -1165,6 +1166,18 @@ module_param_named(hdmi_hpd_debounce_delay_ms, amdgpu_hdmi_hpd_debounce_delay_ms
>   MODULE_PARM_DESC(ptl, "Enable PTL (-1 = auto, 0 = disable (default), 1 = enable, 2 = permanently disable)");
>   module_param_named(ptl, amdgpu_ptl, int, 0444);
>   
> +/**
> + * DOC: ualink_loopback (int)
> + * Enable UALink loopback mode for manufacturing testing. In loopback mode a
> + * single GPU acts as both the exporter (accelerator ID 1) and the importer
> + * (accelerator ID 0) and loops UALink requests back to itself. Possible values:
> + *
> + * - 0 = disable (default)
> + * - 1 = enable
> + */
> +MODULE_PARM_DESC(ualink_loopback, "Enable UALink loopback mode (0 = disable (default), 1 = enable)");
> +module_param_named(ualink_loopback, amdgpu_ualink_loopback, int, 0444);
> +
>   /* These devices are not supported by amdgpu.
>    * They are supported by the mach64, r128, radeon drivers
>    */
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
> index 1c2203ff175d..a98fa5f970b1 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
> @@ -96,11 +96,12 @@ static int amdgpu_ualink_drm_client_create(struct amdgpu_device *adev)
>   /*
>    * amdgpu_ualink_loopback_requested - check whether UALink loopback is requested
>    *
> - * There is no mechanism to request loopback mode yet, so it stays disabled.
> + * Loopback mode is temporarily requested with the amdgpu.ualink_loopback
> + * module parameter.
>    */
>   static bool amdgpu_ualink_loopback_requested(struct amdgpu_device *adev)
>   {
> -	return false;
> +	return amdgpu_ualink_loopback == 1;
>   }
>   
>   /*