text: /*
   * Copyright (C) 2019 Collabora, Ltd.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a
   * copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   * and/or sell copies of the Software, and to permit persons to whom the
   * Software is furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice (including the next
   * paragraph) shall be included in all copies or substantial portions of the
   * Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   *
   * Authors:
   *   Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
   */
  
  #include "util/u_math.h"
  #include "pan_encoder.h"
  
  /* Midgard has a small register file, so shaders with high register pressure
   * need to spill from the register file onto the stack. In addition to
   * spilling, it is desireable to allocate temporary arrays on the stack (for
   * instance because the register file does not support indirect access but the
   * stack does).
   *
   * The stack is located in "Thread Local Storage", sometimes abbreviated TLS in
   * the kernel source code. Thread local storage is allocated per-thread,
   * per-core, so threads executing concurrently do not interfere with each
   * other's stacks. On modern kernels, we may query
   * DRM_PANFROST_PARAM_THREAD_TLS_ALLOC for the number of threads per core we
   * must allocate for, and DRM_PANFROST_PARAM_SHADER_PRESENT for a bitmask of
   * shader cores (so take a popcount of that mask for the number of shader
   * cores). On older kernels that do not support querying these values,
   * following kbase, we may use the worst-case value of 1024 threads for
   * THREAD_TLS_ALLOC, and the worst-case value of 16 cores for Midgard per the
   * "shader core count" column of the implementations table in
   * https://en.wikipedia.org/wiki/Mali_%28GPU% [citation needed]
   *
   * Within a particular thread, there is stack allocated. If it is present, its
   * size is a power-of-two, and it is at least 256 bytes. Stack is allocated
   * with the framebuffer descriptor used for all shaders within a frame (note
   * that they don't execute concurrently so it's fine). So, consider the maximum
   * stack size used by any shader within a job, and then compute (where npot
   * denotes the next power of two):
   *
   *      allocated = npot(max(size, 256)) * (# of threads/core) * (# of cores)
   *
   * The size of Thread Local Storage is signaled to the GPU in a dedicated
   * log_stack_size field. Since stack sizes are powers of two, it follows that
   * stack_size is logarithmic. Consider some sample values:
   *
   *      stack size | log_stack_size
   *      ---------------------------
   *             256 | 4
   *             512 | 5
   *            1024 | 6
   *
   *  Noting that log2(256) = 8, we have the relation:
   *
   *      stack_size <= 2^(log_stack_size + 4)
   *
   *  Given the constraints about powers-of-two and the minimum of 256, we thus
   *  derive a formula for log_stack_size in terms of stack size (s):
   *
   *      log_stack_size = ceil(log2(max(s, 256))) - 4
   *
   * There are other valid characterisations of this formula, of course, but this
   * is computationally simple, so good enough for our purposes.
   */
  
  /* Computes log_stack_size = ceil(log2(max(s, 256))) - 4 */
  
  unsigned
  panfrost_get_stack_shift(unsigned stack_size)
  {
          return util_logbase2_ceil(MAX2(stack_size, 256)) - 4;
  }
  
  /* Computes the aligned stack size given the shift and thread count */
  
  unsigned
  panfrost_get_total_stack_size(
                  unsigned stack_shift,
                  unsigned threads_per_core,
                  unsigned core_count)
  {
          unsigned stack_size = 1 << (stack_shift + 4);
          return stack_size * threads_per_core * core_count;
  }
  