MIPS: Support per-device DMA coherence

On some MIPS systems, a subset of devices may have DMA coherent with CPU
caches. For example in systems including a MIPS I/O Coherence Unit
(IOCU), some devices may be connected to that IOCU whilst others are
not.

Prior to this patch, we have a plat_device_is_coherent() function but no
implementation which does anything besides return a global true or
false, optionally chosen at runtime. For devices such as those described
above this is insufficient.

Fix this by tracking DMA coherence on a per-device basis with a
dma_coherent field in struct dev_archdata. Setting this from
arch_setup_dma_ops() takes care of devices which set the dma-coherent
property via device tree, and any PCI devices beneath a bridge described
in DT, automatically.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14349/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -1099,6 +1099,10 @@ config DMA_MAYBE_COHERENT
 	select DMA_NONCOHERENT
 	bool
 
+config DMA_PERDEV_COHERENT
+	bool
+	select DMA_MAYBE_COHERENT
+
 config DMA_COHERENT
 	bool
 

arch/mips/include/asm/device.h

@@ -11,6 +11,11 @@ struct dma_map_ops;
 struct dev_archdata {
 	/* DMA operations on that device */
 	struct dma_map_ops *dma_ops;
+
+#ifdef CONFIG_DMA_PERDEV_COHERENT
+	/* Non-zero if DMA is coherent with CPU caches */
+	bool dma_coherent;
+#endif
 };
 
 struct pdev_archdata {

arch/mips/include/asm/dma-coherence.h

@@ -15,7 +15,9 @@ enum coherent_io_user_state {
 	IO_COHERENCE_DISABLED,
 };
 
-#ifdef CONFIG_DMA_MAYBE_COHERENT
+#if defined(CONFIG_DMA_PERDEV_COHERENT)
+/* Don't provide (hw_)coherentio to avoid misuse */
+#elif defined(CONFIG_DMA_MAYBE_COHERENT)
 extern enum coherent_io_user_state coherentio;
 extern int hw_coherentio;
 #else

arch/mips/include/asm/dma-mapping.h

@@ -32,4 +32,14 @@ static inline void dma_mark_clean(void *addr, size_t size) {}
 extern void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
 	       enum dma_data_direction direction);
 
+#define arch_setup_dma_ops arch_setup_dma_ops
+static inline void arch_setup_dma_ops(struct device *dev, u64 dma_base,
+				      u64 size, const struct iommu_ops *iommu,
+				      bool coherent)
+{
+#ifdef CONFIG_DMA_PERDEV_COHERENT
+	dev->archdata.dma_coherent = coherent;
+#endif
+}
+
 #endif /* _ASM_DMA_MAPPING_H */

arch/mips/include/asm/mach-generic/dma-coherence.h

@@ -49,6 +49,9 @@ static inline int plat_dma_supported(struct device *dev, u64 mask)
 
 static inline int plat_device_is_coherent(struct device *dev)
 {
+#ifdef CONFIG_DMA_PERDEV_COHERENT
+	return dev->archdata.dma_coherent;
+#else
 	switch (coherentio) {
 	default:
 	case IO_COHERENCE_DEFAULT:
@@ -58,6 +61,7 @@ static inline int plat_device_is_coherent(struct device *dev)
 	case IO_COHERENCE_DISABLED:
 		return 0;
 	}
+#endif
 }
 
 #ifndef plat_post_dma_flush

arch/mips/mm/c-r4k.c

@@ -1935,8 +1935,12 @@ void r4k_cache_init(void)
 	__local_flush_icache_user_range	= local_r4k_flush_icache_user_range;
 
 #if defined(CONFIG_DMA_NONCOHERENT) || defined(CONFIG_DMA_MAYBE_COHERENT)
+# if defined(CONFIG_DMA_PERDEV_COHERENT)
+	if (0) {
+# else
 	if ((coherentio == IO_COHERENCE_ENABLED) ||
 	    ((coherentio == IO_COHERENCE_DEFAULT) && hw_coherentio)) {
+# endif
 		_dma_cache_wback_inv	= (void *)cache_noop;
 		_dma_cache_wback	= (void *)cache_noop;
 		_dma_cache_inv		= (void *)cache_noop;

arch/mips/mm/dma-default.c

@@ -24,7 +24,7 @@
 
 #include <dma-coherence.h>
 
-#ifdef CONFIG_DMA_MAYBE_COHERENT
+#if defined(CONFIG_DMA_MAYBE_COHERENT) && !defined(CONFIG_DMA_PERDEV_COHERENT)
 /* User defined DMA coherency from command line. */
 enum coherent_io_user_state coherentio = IO_COHERENCE_DEFAULT;
 EXPORT_SYMBOL_GPL(coherentio);