Re: [PATCH v3] drm/xe: restrict multi-lrc to VCS/VECS engines

["Wang, X" <x.wang@intel.com>]

On 2/24/2026 14:05, Matt Roper wrote:
> On Mon, Feb 23, 2026 at 06:33:54PM -0800, Xin Wang wrote:
>> Tighten uapi validation to restrict multi-lrc support to VIDEO_DECODE and
>> VIDEO_ENHANCE engines only. This check should have been in place from the
>> start, as the driver typically avoids allowing uapi cases that we have
>> no userspace consumer for.
>>
>> Additionally, the GuC firmware on ModSched platforms no longer supports
>> multi-lrc on non-media engines.
>>
>> V3:
>>   - store a multi-lrc enable class mask in xe->info and populate from
>>     xe_device_desc in xe_pci.c (Matthew Brost)
>>
>> V2:
>>   - correct the typo (Shuicheng)
>>   - move the check earlier to avoid VM lookup (Shuicheng, Matt Roper)
>>   - remove the graphics version check (Matt Roper)
>>   - input more details in the commit info (Matt Roper)
>>
>> Cc: Shuicheng Lin <shuicheng.lin@intel.com>
>> Cc: Matt Roper <matthew.d.roper@intel.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Signed-off-by: Xin Wang <x.wang@intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_device_types.h |  2 ++
>>   drivers/gpu/drm/xe/xe_exec_queue.c   |  5 +++++
>>   drivers/gpu/drm/xe/xe_pci.c          | 17 +++++++++++++++++
>>   drivers/gpu/drm/xe/xe_pci_types.h    |  1 +
>>   4 files changed, 25 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
>> index 8f3ef836541e..caa8f34a6744 100644
>> --- a/drivers/gpu/drm/xe/xe_device_types.h
>> +++ b/drivers/gpu/drm/xe/xe_device_types.h
>> @@ -138,6 +138,8 @@ struct xe_device {
>>   		u8 tile_count;
>>   		/** @info.max_gt_per_tile: Number of GT IDs allocated to each tile */
>>   		u8 max_gt_per_tile;
>> +		/** @info.multi_lrc_mask: bitmask of engine classes which support multi-lrc */
>> +		u8 multi_lrc_mask;
>>   		/** @info.gt_count: Total number of GTs for entire device */
>>   		u8 gt_count;
>>   		/** @info.vm_max_level: Max VM level */
>> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
>> index 66d0e10ee2c4..5abb29454d1f 100644
>> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
>> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
>> @@ -1184,6 +1184,11 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
>>   		if (XE_IOCTL_DBG(xe, !hwe))
>>   			return -EINVAL;
>>   
>> +		/* multi-lrc is only supported on select engine classes */
>> +		if (XE_IOCTL_DBG(xe, args->width > 1 &&
>> +				 !(xe->info.multi_lrc_mask & BIT(hwe->class))))
>> +			return -EOPNOTSUPP;
>> +
>>   		vm = xe_vm_lookup(xef, args->vm_id);
>>   		if (XE_IOCTL_DBG(xe, !vm))
>>   			return -ENOENT;
>> diff --git a/drivers/gpu/drm/xe/xe_pci.c b/drivers/gpu/drm/xe/xe_pci.c
>> index e1f569235d8a..fe63387d4077 100644
>> --- a/drivers/gpu/drm/xe/xe_pci.c
>> +++ b/drivers/gpu/drm/xe/xe_pci.c
>> @@ -194,6 +194,7 @@ static const struct xe_device_desc tgl_desc = {
>>   	.has_llc = true,
>>   	.has_sriov = true,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
> Is there a reason why some platforms list both VCS + VECS but others
> only list VCS?  The new .multi_lrc_mask is intended to restrict usage to
> just the engine type(s) where we have a real userspace consumer, and for
> now I'd expect that to be the same across all current platforms.  We
> should double check whether the media driver is actively using this on
> both media engine types or just one of them (I don't know off the top of
> my head), and then set the mask accordingly.
>
> An ioctl request for multi-LRC might also get rejected on a platform if
> the engine fusing indicates that there aren't 2+ engines of the given
> type, but that's an orthogonal check that's independent of the
> multi_lrc_mask we're defining here.  Finding out how many engines
> actually exist on a device is something that we can only find out at
> runtime after reading the fuse registers for a specific device.
>
>
> Matt
I checked the specs and found that some devices have fewer than two VCS 
or VCES
instances. In these cases, I don't think it's necessary to allow 
multi-LRC to
those engines. This would prevent the injection of some illegal ioctl 
parameters.

Xin
>>   	.require_force_probe = true,
>>   	.va_bits = 48,
>>   	.vm_max_level = 3,
>> @@ -208,6 +209,7 @@ static const struct xe_device_desc rkl_desc = {
>>   	.has_display = true,
>>   	.has_llc = true,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
>>   	.require_force_probe = true,
>>   	.va_bits = 48,
>>   	.vm_max_level = 3,
>> @@ -225,6 +227,7 @@ static const struct xe_device_desc adl_s_desc = {
>>   	.has_llc = true,
>>   	.has_sriov = true,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
>>   	.require_force_probe = true,
>>   	.subplatforms = (const struct xe_subplatform_desc[]) {
>>   		{ XE_SUBPLATFORM_ALDERLAKE_S_RPLS, "RPLS", adls_rpls_ids },
>> @@ -246,6 +249,7 @@ static const struct xe_device_desc adl_p_desc = {
>>   	.has_llc = true,
>>   	.has_sriov = true,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
>>   	.require_force_probe = true,
>>   	.subplatforms = (const struct xe_subplatform_desc[]) {
>>   		{ XE_SUBPLATFORM_ALDERLAKE_P_RPLU, "RPLU", adlp_rplu_ids },
>> @@ -283,6 +287,7 @@ static const struct xe_device_desc dg1_desc = {
>>   	.has_gsc_nvm = 1,
>>   	.has_heci_gscfi = 1,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
>>   	.require_force_probe = true,
>>   	.va_bits = 48,
>>   	.vm_max_level = 3,
>> @@ -313,6 +318,8 @@ static const struct xe_device_desc ats_m_desc = {
>>   	.pre_gmdid_media_ip = &media_ip_xehpm,
>>   	.dma_mask_size = 46,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE) |
>> +			  BIT(XE_ENGINE_CLASS_VIDEO_ENHANCE),
>>   	.require_force_probe = true,
>>   
>>   	DG2_FEATURES,
>> @@ -325,6 +332,8 @@ static const struct xe_device_desc dg2_desc = {
>>   	.pre_gmdid_media_ip = &media_ip_xehpm,
>>   	.dma_mask_size = 46,
>>   	.max_gt_per_tile = 1,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE) |
>> +			  BIT(XE_ENGINE_CLASS_VIDEO_ENHANCE),
>>   	.require_force_probe = true,
>>   
>>   	DG2_FEATURES,
>> @@ -358,6 +367,7 @@ static const struct xe_device_desc mtl_desc = {
>>   	.has_display = true,
>>   	.has_pxp = true,
>>   	.max_gt_per_tile = 2,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE),
>>   	.va_bits = 48,
>>   	.vm_max_level = 3,
>>   };
>> @@ -393,6 +403,8 @@ static const struct xe_device_desc bmg_desc = {
>>   	.has_soc_remapper_telem = true,
>>   	.has_sriov = true,
>>   	.max_gt_per_tile = 2,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE) |
>> +			  BIT(XE_ENGINE_CLASS_VIDEO_ENHANCE),
>>   	.needs_scratch = true,
>>   	.subplatforms = (const struct xe_subplatform_desc[]) {
>>   		{ XE_SUBPLATFORM_BATTLEMAGE_G21, "G21", bmg_g21_ids },
>> @@ -445,6 +457,8 @@ static const struct xe_device_desc cri_desc = {
>>   	.has_soc_remapper_telem = true,
>>   	.has_sriov = true,
>>   	.max_gt_per_tile = 2,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE) |
>> +			  BIT(XE_ENGINE_CLASS_VIDEO_ENHANCE),
>>   	.require_force_probe = true,
>>   	.va_bits = 57,
>>   	.vm_max_level = 4,
>> @@ -459,6 +473,8 @@ static const struct xe_device_desc nvlp_desc = {
>>   	.has_page_reclaim_hw_assist = true,
>>   	.has_pre_prod_wa = true,
>>   	.max_gt_per_tile = 2,
>> +	.multi_lrc_mask = BIT(XE_ENGINE_CLASS_VIDEO_DECODE) |
>> +			  BIT(XE_ENGINE_CLASS_VIDEO_ENHANCE),
>>   	.require_force_probe = true,
>>   	.va_bits = 48,
>>   	.vm_max_level = 4,
>> @@ -746,6 +762,7 @@ static int xe_info_init_early(struct xe_device *xe,
>>   	xe->info.skip_pcode = desc->skip_pcode;
>>   	xe->info.needs_scratch = desc->needs_scratch;
>>   	xe->info.needs_shared_vf_gt_wq = desc->needs_shared_vf_gt_wq;
>> +	xe->info.multi_lrc_mask = desc->multi_lrc_mask;
>>   
>>   	xe->info.probe_display = IS_ENABLED(CONFIG_DRM_XE_DISPLAY) &&
>>   				 xe_modparam.probe_display &&
>> diff --git a/drivers/gpu/drm/xe/xe_pci_types.h b/drivers/gpu/drm/xe/xe_pci_types.h
>> index 470d31a1f0d6..47e8a1552c2b 100644
>> --- a/drivers/gpu/drm/xe/xe_pci_types.h
>> +++ b/drivers/gpu/drm/xe/xe_pci_types.h
>> @@ -30,6 +30,7 @@ struct xe_device_desc {
>>   	u8 dma_mask_size;
>>   	u8 max_remote_tiles:2;
>>   	u8 max_gt_per_tile:2;
>> +	u8 multi_lrc_mask;
>>   	u8 va_bits;
>>   	u8 vm_max_level;
>>   	u8 vram_flags;
>> -- 
>> 2.43.0
>>