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drm: omapdrm: Fix incorrect usage of the term 'cache coherency'

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The is_cache_coherent() function currently returns true when the mapping
is not cache-coherent. This isn't a bug as such as the callers interpret
cache-coherent as meaning that the driver has to handle the coherency
manually, but it is nonetheless very confusing. Fix it and add a bit
more documentation to explain how cached buffers are handled.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
This commit is contained in:
Laurent Pinchart 2017-04-21 00:33:56 +03:00 committed by Tomi Valkeinen
parent d61ce7da02
commit 24fbaca0e2
1 changed files with 15 additions and 7 deletions
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22
drivers/gpu/drm/omapdrm/omap_gem.c
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@ -719,16 +719,21 @@ int omap_gem_roll(struct drm_gem_object *obj, uint32_t roll)
* Memory Management & DMA Sync
*/
/**
* shmem buffers that are mapped cached can simulate coherency via using
* page faulting to keep track of dirty pages
/*
* shmem buffers that are mapped cached are not coherent.
*
* We keep track of dirty pages using page faulting to perform cache management.
* When a page is mapped to the CPU in read/write mode the device can't access
* it and omap_obj->dma_addrs[i] is NULL. When a page is mapped to the device
* the omap_obj->dma_addrs[i] is set to the DMA address, and the page is
* unmapped from the CPU.
*/
static inline bool is_cached_coherent(struct drm_gem_object *obj)
{
struct omap_gem_object *omap_obj = to_omap_bo(obj);
return (omap_obj->flags & OMAP_BO_MEM_SHMEM) &&
((omap_obj->flags & OMAP_BO_CACHE_MASK) == OMAP_BO_CACHED);
return !((omap_obj->flags & OMAP_BO_MEM_SHMEM) &&
((omap_obj->flags & OMAP_BO_CACHE_MASK) == OMAP_BO_CACHED));
}
/* Sync the buffer for CPU access.. note pages should already be
@ -739,7 +744,10 @@ void omap_gem_cpu_sync_page(struct drm_gem_object *obj, int pgoff)
struct drm_device *dev = obj->dev;
struct omap_gem_object *omap_obj = to_omap_bo(obj);
if (is_cached_coherent(obj) && omap_obj->dma_addrs[pgoff]) {
if (is_cached_coherent(obj))
return;
if (omap_obj->dma_addrs[pgoff]) {
dma_unmap_page(dev->dev, omap_obj->dma_addrs[pgoff],
PAGE_SIZE, DMA_BIDIRECTIONAL);
omap_obj->dma_addrs[pgoff] = 0;
@ -756,7 +764,7 @@ void omap_gem_dma_sync_buffer(struct drm_gem_object *obj,
struct page **pages = omap_obj->pages;
bool dirty = false;
if (!is_cached_coherent(obj))
if (is_cached_coherent(obj))
return;
for (i = 0; i < npages; i++) {