Revert "drm/xe/lnl: Offload system clear page activity to GPU"

This optimization relied on having to clear CCS on allocations.
If there is no need to clear CCS on allocations then this would mostly
help in reducing CPU utilization.

Revert this patch at this moment because of:
1 Currently Xe can't do clear on free and using a invalid ttm flag,
TTM_TT_FLAG_CLEARED_ON_FREE which could poison global ttm pool on
multi-device setup.

2 Also for LNL CPU:WB doesn't require clearing CCS as such BO will
not be allowed to bind with compression PTE. Subsequent patch will
disable clearing CCS for CPU:WB BOs for LNL.

This reverts commit 23683061805be368c8d1c7e7ff52abc470cac275.

Cc: Christian König <[e-mail]>
Cc: Himal Prasad Ghimiray <[e-mail]>
Cc: Lucas De Marchi <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Cc: Matthew Brost <[e-mail]>
Cc: Thomas Hellström <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]>
Signed-off-by: Nirmoy Das <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/xe_bo.c

···
 		caching = ttm_uncached;
 	}
 
-	/*
-	 * If the device can support gpu clear system pages then set proper ttm
-	 * flag. Zeroed pages are only required for ttm_bo_type_device so
-	 * unwanted data is not leaked to userspace.
-	 */
-	if (ttm_bo->type == ttm_bo_type_device && xe->mem.gpu_page_clear_sys)
-		page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE;
-
 	err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages);
 	if (err) {
 		kfree(tt);
···
 	 */
 	if (tt->page_flags & TTM_TT_FLAG_EXTERNAL)
 		return 0;
-
-	/* Clear TTM_TT_FLAG_ZERO_ALLOC when GPU is set to clear system pages */
-	if (tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE)
-		tt->page_flags &= ~TTM_TT_FLAG_ZERO_ALLOC;
 
 	err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx);
 	if (err)
···
 	bool needs_clear;
 	bool handle_system_ccs = (!IS_DGFX(xe) && xe_bo_needs_ccs_pages(bo) &&
 				  ttm && ttm_tt_is_populated(ttm)) ? true : false;
-	bool clear_system_pages;
 	int ret = 0;
-
-	/*
-	 * Clear TTM_TT_FLAG_CLEARED_ON_FREE on bo creation path when
-	 * moving to system as the bo doesn't have dma_mapping.
-	 */
-	if (!old_mem && ttm && !ttm_tt_is_populated(ttm))
-		ttm->page_flags &= ~TTM_TT_FLAG_CLEARED_ON_FREE;
 
 	/* Bo creation path, moving to system or TT. */
 	if ((!old_mem && ttm) && !handle_system_ccs) {
···
 	move_lacks_source = handle_system_ccs ? (!bo->ccs_cleared)  :
 						(!mem_type_is_vram(old_mem_type) && !tt_has_data);
 
-	clear_system_pages = ttm && (ttm->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE);
 	needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) ||
-		(!ttm && ttm_bo->type == ttm_bo_type_device) ||
-		clear_system_pages;
+		(!ttm && ttm_bo->type == ttm_bo_type_device);
 
 	if (new_mem->mem_type == XE_PL_TT) {
 		ret = xe_tt_map_sg(ttm);
···
 		if (move_lacks_source) {
 			u32 flags = 0;
 
-			if (mem_type_is_vram(new_mem->mem_type) || clear_system_pages)
+			if (mem_type_is_vram(new_mem->mem_type))
 				flags |= XE_MIGRATE_CLEAR_FLAG_FULL;
 			else if (handle_system_ccs)
 				flags |= XE_MIGRATE_CLEAR_FLAG_CCS_DATA;

drivers/gpu/drm/xe/xe_device_types.h

···
 		struct xe_mem_region vram;
 		/** @mem.sys_mgr: system TTM manager */
 		struct ttm_resource_manager sys_mgr;
-		/** @mem.gpu_page_clear_sys: clear system pages offloaded to GPU */
-		bool gpu_page_clear_sys;
 	} mem;
 
 	/** @sriov: device level virtualization data */

drivers/gpu/drm/xe/xe_ttm_sys_mgr.c

···
 	ttm_resource_manager_init(man, &xe->ttm, gtt_size >> PAGE_SHIFT);
 	ttm_set_driver_manager(&xe->ttm, XE_PL_TT, man);
 	ttm_resource_manager_set_used(man, true);
-
-	/*
-	 * On iGFX device with flat CCS, we clear CCS metadata, let's extend that
-	 * and use GPU to clear pages as well.
-	 *
-	 * Disable this when init_on_free and/or init_on_alloc is on to avoid double
-	 * zeroing pages with CPU and GPU.
-	 */
-	if (xe_device_has_flat_ccs(xe) && !IS_DGFX(xe) &&
-	    !want_init_on_alloc(GFP_USER) && !want_init_on_free())
-		xe->mem.gpu_page_clear_sys = true;
-
 	return drmm_add_action_or_reset(&xe->drm, ttm_sys_mgr_fini, xe);
 }