xtensa: platform-specific handling of coherent memory

Memory layout is not fixed for noMMU xtensa configurations. Platforms
that need to use coherent DMA should implement platform_vaddr_* helpers
that check address type (cached/uncached) and convert addresses between
these types.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/kmem_layout.h

@@ -63,12 +63,6 @@
 #error XCHAL_KSEG_PADDR is not properly aligned to XCHAL_KSEG_ALIGNMENT
 #endif
 
-#else
-
-#define XCHAL_KSEG_CACHED_VADDR	__XTENSA_UL_CONST(0xd0000000)
-#define XCHAL_KSEG_BYPASS_VADDR	__XTENSA_UL_CONST(0xd8000000)
-#define XCHAL_KSEG_SIZE		__XTENSA_UL_CONST(0x08000000)
-
 #endif
 
 #ifndef CONFIG_KASAN

arch/xtensa/include/asm/pgtable.h

@@ -66,6 +66,7 @@
 #define FIRST_USER_ADDRESS	0UL
 #define FIRST_USER_PGD_NR	(FIRST_USER_ADDRESS >> PGDIR_SHIFT)
 
+#ifdef CONFIG_MMU
 /*
  * Virtual memory area. We keep a distance to other memory regions to be
  * on the safe side. We also use this area for cache aliasing.
@@ -80,6 +81,13 @@
 #define TLBTEMP_SIZE		ICACHE_WAY_SIZE
 #endif
 
+#else
+
+#define VMALLOC_START		__XTENSA_UL_CONST(0)
+#define VMALLOC_END		__XTENSA_UL_CONST(0xffffffff)
+
+#endif
+
 /*
  * For the Xtensa architecture, the PTE layout is as follows:
  *

arch/xtensa/include/asm/platform.h

@@ -75,4 +75,31 @@ extern void platform_calibrate_ccount (void);
  */
 void cpu_reset(void) __attribute__((noreturn));
 
+/*
+ * Memory caching is platform-dependent in noMMU xtensa configurations.
+ * The following set of functions should be implemented in platform code
+ * in order to enable coherent DMA memory operations when CONFIG_MMU is not
+ * enabled. Default implementations do nothing and issue a warning.
+ */
+
+/*
+ * Check whether p points to a cached memory.
+ */
+bool platform_vaddr_cached(const void *p);
+
+/*
+ * Check whether p points to an uncached memory.
+ */
+bool platform_vaddr_uncached(const void *p);
+
+/*
+ * Return pointer to an uncached view of the cached sddress p.
+ */
+void *platform_vaddr_to_uncached(void *p);
+
+/*
+ * Return pointer to a cached view of the uncached sddress p.
+ */
+void *platform_vaddr_to_cached(void *p);
+
 #endif	/* _XTENSA_PLATFORM_H */

arch/xtensa/kernel/pci-dma.c

@@ -24,6 +24,7 @@
 #include <linux/types.h>
 #include <asm/cacheflush.h>
 #include <asm/io.h>
+#include <asm/platform.h>
 
 static void do_cache_op(phys_addr_t paddr, size_t size,
 			void (*fn)(unsigned long, unsigned long))
@@ -84,6 +85,58 @@ void arch_sync_dma_for_device(struct device *dev, phys_addr_t paddr,
 	}
 }
 
+#ifdef CONFIG_MMU
+bool platform_vaddr_cached(const void *p)
+{
+	unsigned long addr = (unsigned long)p;
+
+	return addr >= XCHAL_KSEG_CACHED_VADDR &&
+	       addr - XCHAL_KSEG_CACHED_VADDR < XCHAL_KSEG_SIZE;
+}
+
+bool platform_vaddr_uncached(const void *p)
+{
+	unsigned long addr = (unsigned long)p;
+
+	return addr >= XCHAL_KSEG_BYPASS_VADDR &&
+	       addr - XCHAL_KSEG_BYPASS_VADDR < XCHAL_KSEG_SIZE;
+}
+
+void *platform_vaddr_to_uncached(void *p)
+{
+	return p + XCHAL_KSEG_BYPASS_VADDR - XCHAL_KSEG_CACHED_VADDR;
+}
+
+void *platform_vaddr_to_cached(void *p)
+{
+	return p + XCHAL_KSEG_CACHED_VADDR - XCHAL_KSEG_BYPASS_VADDR;
+}
+#else
+bool __attribute__((weak)) platform_vaddr_cached(const void *p)
+{
+	WARN_ONCE(1, "Default %s implementation is used\n", __func__);
+	return true;
+}
+
+bool __attribute__((weak)) platform_vaddr_uncached(const void *p)
+{
+	WARN_ONCE(1, "Default %s implementation is used\n", __func__);
+	return false;
+}
+
+void __attribute__((weak)) *platform_vaddr_to_uncached(void *p)
+{
+	WARN_ONCE(1, "Default %s implementation is used\n", __func__);
+	return p;
+}
+
+void __attribute__((weak)) *platform_vaddr_to_cached(void *p)
+{
+	WARN_ONCE(1, "Default %s implementation is used\n", __func__);
+	return p;
+}
+#endif
+
 /*
  * Note: We assume that the full memory space is always mapped to 'kseg'
  *	 Otherwise we have to use page attributes (not implemented).
@@ -92,8 +145,6 @@ void arch_sync_dma_for_device(struct device *dev, phys_addr_t paddr,
 void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 		gfp_t flag, unsigned long attrs)
 {
-	unsigned long ret;
-	unsigned long uncached;
 	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 	struct page *page = NULL;
 
@@ -134,29 +185,21 @@ void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 		return p;
 	}
 #endif
-	ret = (unsigned long)page_address(page);
-	BUG_ON(ret < XCHAL_KSEG_CACHED_VADDR ||
-	       ret > XCHAL_KSEG_CACHED_VADDR + XCHAL_KSEG_SIZE - 1);
-
-	uncached = ret + XCHAL_KSEG_BYPASS_VADDR - XCHAL_KSEG_CACHED_VADDR;
-	__invalidate_dcache_range(ret, size);
-
-	return (void *)uncached;
+	BUG_ON(!platform_vaddr_cached(page_address(page)));
+	__invalidate_dcache_range((unsigned long)page_address(page), size);
+	return platform_vaddr_to_uncached(page_address(page));
 }
 
 void arch_dma_free(struct device *dev, size_t size, void *vaddr,
 		dma_addr_t dma_handle, unsigned long attrs)
 {
 	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-	unsigned long addr = (unsigned long)vaddr;
 	struct page *page;
 
 	if (attrs & DMA_ATTR_NO_KERNEL_MAPPING) {
 		page = vaddr;
-	} else if (addr >= XCHAL_KSEG_BYPASS_VADDR &&
-		   addr - XCHAL_KSEG_BYPASS_VADDR < XCHAL_KSEG_SIZE) {
-		addr += XCHAL_KSEG_CACHED_VADDR - XCHAL_KSEG_BYPASS_VADDR;
-		page = virt_to_page(addr);
+	} else if (platform_vaddr_uncached(vaddr)) {
+		page = virt_to_page(platform_vaddr_to_cached(vaddr));
 	} else {
 #ifdef CONFIG_MMU
 		dma_common_free_remap(vaddr, size, VM_MAP);