Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used
From: Robin Murphy
Date: Wed Feb 14 2024 - 12:24:41 EST
On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
Some platforms do have DMA, but DMA there is always direct and coherent.
Currently, even on such platforms DMA sync operations are compiled and
called.
Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
either sync operations are needed or there is DMA ops or swiotlb
enabled. Set dma_need_sync() and dma_skip_sync() depending on this
symbol state and don't call sync ops when dma_skip_sync() is true.
The change allows for future optimizations of DMA sync calls depending
on compile-time or runtime conditions.
Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
kernel/dma/Kconfig | 4 ++
include/linux/dma-mapping.h | 80 +++++++++++++++++++++++++++++++------
kernel/dma/mapping.c | 20 +++++-----
3 files changed, 81 insertions(+), 23 deletions(-)
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index d62f5957f36b..1c9ff05b1ecb 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -107,6 +107,10 @@ config DMA_BOUNCE_UNALIGNED_KMALLOC
bool
depends on SWIOTLB
+config DMA_NEED_SYNC
+ def_bool ARCH_HAS_SYNC_DMA_FOR_DEVICE || ARCH_HAS_SYNC_DMA_FOR_CPU || \
+ ARCH_HAS_SYNC_DMA_FOR_CPU_ALL || DMA_OPS || SWIOTLB
I'm not sure DMA_OPS belongs here - several architectures have
non-trivial ops without syncs, e.g. Alpha.
+
config DMA_RESTRICTED_POOL
bool "DMA Restricted Pool"
depends on OF && OF_RESERVED_MEM && SWIOTLB
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4a658de44ee9..6c7640441214 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -117,13 +117,13 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
size_t size, enum dma_data_direction dir, unsigned long attrs);
void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
enum dma_data_direction dir, unsigned long attrs);
-void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
+void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
enum dma_data_direction dir);
-void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
+void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
size_t size, enum dma_data_direction dir);
-void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
int nelems, enum dma_data_direction dir);
-void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
int nelems, enum dma_data_direction dir);
void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
gfp_t flag, unsigned long attrs);
@@ -147,7 +147,7 @@ u64 dma_get_required_mask(struct device *dev);
bool dma_addressing_limited(struct device *dev);
size_t dma_max_mapping_size(struct device *dev);
size_t dma_opt_mapping_size(struct device *dev);
-bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
+bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr);
unsigned long dma_get_merge_boundary(struct device *dev);
struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
enum dma_data_direction dir, gfp_t gfp, unsigned long attrs);
@@ -195,19 +195,19 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
size_t size, enum dma_data_direction dir, unsigned long attrs)
{
}
-static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
- size_t size, enum dma_data_direction dir)
+static inline void __dma_sync_single_for_cpu(struct device *dev,
+ dma_addr_t addr, size_t size, enum dma_data_direction dir)
To me it would feel more logical to put all the wrappers inside the
#ifdef CONFIG_HAS_DMA and not touch these stubs at all (what does it
mean to skip an inline no-op?). Or in fact, if dma_skip_sync() is
constant false for !HAS_DMA, then we could also just make the external
function declarations unconditional and remove the stubs. Not a critical
matter though, and I defer to whatever Christoph thinks is most
maintainable.
{
}
-static inline void dma_sync_single_for_device(struct device *dev,
+static inline void __dma_sync_single_for_device(struct device *dev,
dma_addr_t addr, size_t size, enum dma_data_direction dir)
{
}
-static inline void dma_sync_sg_for_cpu(struct device *dev,
+static inline void __dma_sync_sg_for_cpu(struct device *dev,
struct scatterlist *sg, int nelems, enum dma_data_direction dir)
{
}
-static inline void dma_sync_sg_for_device(struct device *dev,
+static inline void __dma_sync_sg_for_device(struct device *dev,
struct scatterlist *sg, int nelems, enum dma_data_direction dir)
{
}
@@ -277,7 +277,7 @@ static inline size_t dma_opt_mapping_size(struct device *dev)
{
return 0;
}
-static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
+static inline bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
{
return false;
}
@@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
}
+static inline void __dma_sync_single_range_for_cpu(struct device *dev,
+ dma_addr_t addr, unsigned long offset, size_t size,
+ enum dma_data_direction dir)
+{
+ __dma_sync_single_for_cpu(dev, addr + offset, size, dir);
+}
+
+static inline void __dma_sync_single_range_for_device(struct device *dev,
+ dma_addr_t addr, unsigned long offset, size_t size,
+ enum dma_data_direction dir)
+{
+ __dma_sync_single_for_device(dev, addr + offset, size, dir);
+}
There is no need to introduce these two.
+
+static inline bool dma_skip_sync(const struct device *dev)
+{
+ return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
+}
+
+static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
+{
+ return !dma_skip_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
+}
That's a bit of a mind-bender... is it actually just
return !dma_skip_sync(dev) && __dma_need_sync(dev, dma_addr);
?
(I do still think the negative flag makes it all a little harder to
follow in general than a positive "device needs to consider syncs" flag
would.)
+static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
+ size_t size, enum dma_data_direction dir)
+{
+ if (!dma_skip_sync(dev))
+ __dma_sync_single_for_cpu(dev, addr, size, dir);
+}
+
+static inline void dma_sync_single_for_device(struct device *dev,
+ dma_addr_t addr, size_t size, enum dma_data_direction dir)
+{
+ if (!dma_skip_sync(dev))
+ __dma_sync_single_for_device(dev, addr, size, dir);
+}
+
+static inline void dma_sync_sg_for_cpu(struct device *dev,
+ struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+{
+ if (!dma_skip_sync(dev))
+ __dma_sync_sg_for_cpu(dev, sg, nelems, dir);
+}
+
+static inline void dma_sync_sg_for_device(struct device *dev,
+ struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+{
+ if (!dma_skip_sync(dev))
+ __dma_sync_sg_for_device(dev, sg, nelems, dir);
+}
+
static inline void dma_sync_single_range_for_cpu(struct device *dev,
dma_addr_t addr, unsigned long offset, size_t size,
enum dma_data_direction dir)
{
- return dma_sync_single_for_cpu(dev, addr + offset, size, dir);
+ if (!dma_skip_sync(dev))
+ __dma_sync_single_for_cpu(dev, addr + offset, size, dir);
}
static inline void dma_sync_single_range_for_device(struct device *dev,
dma_addr_t addr, unsigned long offset, size_t size,
enum dma_data_direction dir)
{
- return dma_sync_single_for_device(dev, addr + offset, size, dir);
+ if (!dma_skip_sync(dev))
+ __dma_sync_single_for_device(dev, addr + offset, size, dir);
}
These two don't need changing either, since the dma_sync_single_*
wrappers have already taken care of it.
Thanks,
Robin.