drm/amdkfd: Add more comments on GFX9 user CP queue MQD workaround

	int retval;

	struct kfd_mem_obj *mqd_mem_obj = NULL;

	/* From V9,  for CWSR, the control stack is located on the next page

	 * boundary after the mqd, we will use the gtt allocation function

	 * instead of sub-allocation function.

	/* For V9 only, due to a HW bug, the control stack of a user mode

	 * compute queue needs to be allocated just behind the page boundary

	 * of its regular MQD buffer. So we allocate an enlarged MQD buffer:

	 * the first page of the buffer serves as the regular MQD buffer

	 * purpose and the remaining is for control stack. Although the two

	 * parts are in the same buffer object, they need different memory

	 * types: MQD part needs UC (uncached) as usual, while control stack

	 * needs NC (non coherent), which is different from the UC type which

	 * is used when control stack is allocated in user space.

	 *

	 * Because of all those, we use the gtt allocation function instead

	 * of sub-allocation function for this enlarged MQD buffer. Moreover,

	 * in order to achieve two memory types in a single buffer object, we

	 * pass a special bo flag AMDGPU_GEM_CREATE_CP_MQD_GFX9 to instruct

	 * amdgpu memory functions to do so.

	 */

	if (kfd->cwsr_enabled && (q->type == KFD_QUEUE_TYPE_COMPUTE)) {

		mqd_mem_obj = kzalloc(sizeof(struct kfd_mem_obj), GFP_KERNEL);