dma: fix DMA sync for drivers not calling dma_set_mask*()

There are several reports that the DMA sync shortcut broke non-coherent
devices.
dev->dma_need_sync is false after the &device allocation and if a driver
didn't call dma_set_mask*(), it will still be false even if the device
is not DMA-coherent and thus needs synchronizing. Due to historical
reasons, there's still a lot of drivers not calling it.
Invert the boolean, so that the sync will be performed by default and
the shortcut will be enabled only when calling dma_set_mask*().

Reported-by: Steven Price <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]
Reported-by: Marek Szyprowski <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]
Fixes: f406c8e. ("dma: avoid redundant calls for sync operations")
Signed-off-by: Alexander Lobakin <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Steven Price <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>

Author: alobakin

include/linux/device.h

@@ -691,7 +691,7 @@ struct device_physical_location {
  *		and optionall (if the coherent mask is large enough) also
  *		for dma allocations.  This flag is managed by the dma ops
  *		instance from ->dma_supported.
- * @dma_need_sync: The device needs performing DMA sync operations.
+ * @dma_skip_sync: DMA sync operations can be skipped for coherent buffers.
  *
  * At the lowest level, every device in a Linux system is represented by an
  * instance of struct device. The device structure contains the information
@@ -805,7 +805,7 @@ struct device {
 	bool			dma_ops_bypass : 1;
 #endif
 #ifdef CONFIG_DMA_NEED_SYNC
-	bool			dma_need_sync:1;
+	bool			dma_skip_sync:1;
 #endif
 };
 

include/linux/dma-map-ops.h

@@ -280,8 +280,8 @@ static inline void dma_reset_need_sync(struct device *dev)
 {
 #ifdef CONFIG_DMA_NEED_SYNC
 	/* Reset it only once so that the function can be called on hotpath */
-	if (unlikely(!dev->dma_need_sync))
-		dev->dma_need_sync = true;
+	if (unlikely(dev->dma_skip_sync))
+		dev->dma_skip_sync = false;
 #endif
 }
 

include/linux/dma-mapping.h

@@ -295,7 +295,7 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr);
 static inline bool dma_dev_need_sync(const struct device *dev)
 {
 	/* Always call DMA sync operations when debugging is enabled */
-	return dev->dma_need_sync || IS_ENABLED(CONFIG_DMA_API_DEBUG);
+	return !dev->dma_skip_sync || IS_ENABLED(CONFIG_DMA_API_DEBUG);
 }
 
 static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,

kernel/dma/mapping.c

@@ -392,7 +392,7 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 
 	if (dma_map_direct(dev, ops))
 		/*
-		 * dma_need_sync could've been reset on first SWIOTLB buffer
+		 * dma_skip_sync could've been reset on first SWIOTLB buffer
 		 * mapping, but @dma_addr is not necessary an SWIOTLB buffer.
 		 * In this case, fall back to more granular check.
 		 */
@@ -407,20 +407,20 @@ static void dma_setup_need_sync(struct device *dev)
 
 	if (dma_map_direct(dev, ops) || (ops->flags & DMA_F_CAN_SKIP_SYNC))
 		/*
-		 * dma_need_sync will be reset to %true on first SWIOTLB buffer
+		 * dma_skip_sync will be reset to %false on first SWIOTLB buffer
 		 * mapping, if any. During the device initialization, it's
 		 * enough to check only for the DMA coherence.
 		 */
-		dev->dma_need_sync = !dev_is_dma_coherent(dev);
+		dev->dma_skip_sync = dev_is_dma_coherent(dev);
 	else if (!ops->sync_single_for_device && !ops->sync_single_for_cpu &&
 		 !ops->sync_sg_for_device && !ops->sync_sg_for_cpu)
 		/*
 		 * Synchronization is not possible when none of DMA sync ops
 		 * is set.
 		 */
-		dev->dma_need_sync = false;
+		dev->dma_skip_sync = true;
 	else
-		dev->dma_need_sync = true;
+		dev->dma_skip_sync = false;
 }
 #else /* !CONFIG_DMA_NEED_SYNC */
 static inline void dma_setup_need_sync(struct device *dev) { }

kernel/dma/swiotlb.c

@@ -1409,7 +1409,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
 	}
 
 	/*
-	 * If dma_need_sync wasn't set, reset it on first SWIOTLB buffer
+	 * If dma_skip_sync was set, reset it on first SWIOTLB buffer
 	 * mapping to always sync SWIOTLB buffers.
 	 */
 	dma_reset_need_sync(dev);