include/drm/drm_cache.h

   1 /**************************************************************************
   2  *
   3  * Copyright 2009 Red Hat Inc.
   4  * All Rights Reserved.
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  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
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  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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  27  **************************************************************************/
  28 /*
  29  * Authors:
  30  * Dave Airlie <airlied@redhat.com>
  31  */
  32
  33 #ifndef _DRM_CACHE_H_
  34 #define _DRM_CACHE_H_
  35
  36 #include <linux/scatterlist.h>
  37
  38 void drm_clflush_pages(struct page *pages[], unsigned long num_pages);
  39 void drm_clflush_sg(struct sg_table *st);
  40 void drm_clflush_virt_range(void *addr, unsigned long length);
  41
  42 static inline bool drm_arch_can_wc_memory(void)
  43 {
  44 #if defined(CONFIG_PPC) && !defined(CONFIG_NOT_COHERENT_CACHE)
  45         return false;
  46 #elif defined(CONFIG_MIPS) && defined(CONFIG_CPU_LOONGSON3)
  47         return false;
  48 #elif defined(CONFIG_ARM) || defined(CONFIG_ARM64)
  49         /*
  50          * The DRM driver stack is designed to work with cache coherent devices
  51          * only, but permits an optimization to be enabled in some cases, where
  52          * for some buffers, both the CPU and the GPU use uncached mappings,
  53          * removing the need for DMA snooping and allocation in the CPU caches.
  54          *
  55          * The use of uncached GPU mappings relies on the correct implementation
  56          * of the PCIe NoSnoop TLP attribute by the platform, otherwise the GPU
  57          * will use cached mappings nonetheless. On x86 platforms, this does not
  58          * seem to matter, as uncached CPU mappings will snoop the caches in any
  59          * case. However, on ARM and arm64, enabling this optimization on a
  60          * platform where NoSnoop is ignored results in loss of coherency, which
  61          * breaks correct operation of the device. Since we have no way of
  62          * detecting whether NoSnoop works or not, just disable this
  63          * optimization entirely for ARM and arm64.
  64          */
  65         return false;
  66 #else
  67         return true;
  68 #endif
  69 }
  70
  71 #endif