ARM: UNOFFICIAL_USER_DMA_API

ARM: UNOFFICIAL_USER_DMA_API

Signed-off-by: Russell King <linux@arm.linux.org.uk>

5 files changed, 130 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 03d7519a75fa..9f6e9b58bf96 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1268,6 +1268,25 @@ config UACCESS_WITH_MEMCPY
 	  However, if the CPU data cache is using a write-allocate mode,
 	  this option is unlikely to provide any performance gain.
 
+config UNOFFICIAL_USER_DMA_API
+	bool "Enable unofficial user DMA API (READ HELP TEXT)"
+	depends on EXPERIMENTAL
+	help
+	  This option enables the exposure of the kernel's three DMA cache
+	  coherence functions to userspace via three ARM private syscalls.
+
+	  This API is not officially supported; it is a stop gap measure
+	  to allow developers to achieve their goals.  It doesn't take
+	  account of any DMA restrictions which may be in the system, and
+	  makes no attempt to work around those.
+
+	  The user is entirely responsible for coordinating the use of this
+	  API with DMA activity and CPU snooping activity.  Improper use
+	  of this API can result in random data corruption, especially if
+	  the memory contains DMA scatterlists.
+
+	  Use of this API will taint the kernel.
+
 endmenu
 
 menu "Boot options"
diff --git a/arch/arm/configs/omap_4430sdp_defconfig b/arch/arm/configs/omap_4430sdp_defconfig
index 54d5edb0ee15..c900c4897813 100644
--- a/arch/arm/configs/omap_4430sdp_defconfig
+++ b/arch/arm/configs/omap_4430sdp_defconfig
@@ -255,7 +255,7 @@ CONFIG_ARM_L1_CACHE_SHIFT=5
 # CONFIG_ARM_ERRATA_460075 is not set
 CONFIG_PL310_ERRATA_588369=y
 CONFIG_ARM_GIC=y
-
+CONFIG_UNOFFICIAL_USER_DMA_API=y
 #
 # Bus support
 #
diff --git a/arch/arm/include/asm/unistd.h b/arch/arm/include/asm/unistd.h
index 4e506d09e5f9..1298ea98909b 100644
--- a/arch/arm/include/asm/unistd.h
+++ b/arch/arm/include/asm/unistd.h
@@ -406,7 +406,17 @@
  * *NOTE*: This is a ghost syscall private to the kernel.  Only the
  * __kuser_cmpxchg code in entry-armv.S should be aware of its
  * existence.  Don't ever use this from user code.
+=======
+ * These are temporary interfaces; they are a stop gap until we get
+ * a proper solution to DMA.  These won't always work for every
+ * device.  Only use these IF you *really* know what you're doing.
+ * Don't be surprised if they go away in later kernels.
+>>>>>>> ARM: UNOFFICIAL_USER_DMA_API:arch/arm/include/asm/unistd.h
  */
+#define __ARM_NR_temp_dma_inv_range	(__ARM_NR_BASE+0x0007fd)
+#define __ARM_NR_temp_dma_clean_range	(__ARM_NR_BASE+0x0007fe)
+#define __ARM_NR_temp_dma_flush_range	(__ARM_NR_BASE+0x0007ff)
+
 #ifdef __KERNEL__
 #define __ARM_NR_cmpxchg		(__ARM_NR_BASE+0x00fff0)
 #endif
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 23d76738ff7b..10098ed778e5 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -422,7 +422,7 @@ static int bad_syscall(int n, struct pt_regs *regs)
 	return regs->ARM_r0;
 }
 
-static inline void
+static void
 do_cache_op(unsigned long start, unsigned long end, int flags)
 {
 	struct mm_struct *mm = current->active_mm;
@@ -517,6 +517,22 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 #endif
 		return 0;
 
+#ifdef CONFIG_UNOFFICIAL_USER_DMA_API
+	/*
+	 * These are temporary interfaces; they are a stop gap until we get
+	 * a proper solution to DMA.  These won't always work for every
+	 * device.  Only use these IF you *really* know what you're doing.
+	 * Don't be surprised if they go away in later kernels.
+	 */
+	case NR(temp_dma_inv_range):
+	case NR(temp_dma_clean_range):
+	case NR(temp_dma_flush_range):
+	{
+		extern int temp_user_dma_op(unsigned long, unsigned long, int);
+		return temp_user_dma_op(regs->ARM_r0, regs->ARM_r1, no & 3);
+	}
+#endif
+
 #ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
 	/*
 	 * Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 64daef2173bd..940d44b3c59d 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -614,3 +614,86 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 	}
 }
 EXPORT_SYMBOL(dma_sync_sg_for_device);
+
+#ifdef CONFIG_UNOFFICIAL_USER_DMA_API
+int temp_user_dma_op(unsigned long start, unsigned long end, int op)
+{
+	struct mm_struct *mm = current->active_mm;
+	void (*inner_op)(const void *, const void *);
+	void (*outer_op)(unsigned long, unsigned long);
+
+	if (!test_taint(TAINT_USER)) {
+		printk(KERN_WARNING "%s: using unofficial user DMA API, kernel tainted.\n",
+			current->comm);
+		add_taint(TAINT_USER);
+	}
+
+	switch (op) {
+	case 1:
+		inner_op = dmac_inv_range;
+		outer_op = outer_inv_range;
+		break;
+	case 2:
+		inner_op = dmac_clean_range;
+		outer_op = outer_clean_range;
+		break;
+	case 3:
+		inner_op = dmac_flush_range;
+		outer_op = outer_flush_range;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (end < start)
+		return -EINVAL;
+
+	down_read(&mm->mmap_sem);
+	do {
+		struct vm_area_struct *vma = find_vma(mm, start);
+
+		if (!vma || start < vma->vm_start ||
+		    vma->vm_flags & (VM_IO | VM_PFNMAP)) {
+			up_read(&mm->mmap_sem);
+			return -EFAULT;
+		}
+
+		do {
+			unsigned long e = (start | ~PAGE_MASK) + 1;
+			struct page *page;
+
+			if (e > end)
+				e = end;
+
+			page = follow_page(vma, start, FOLL_GET);
+			if (IS_ERR(page)) {
+				up_read(&mm->mmap_sem);
+				return PTR_ERR(page);
+			}
+
+			if (page) {
+				unsigned long phys;
+
+				/*
+				 * This flushes the userspace address - which
+				 * is not what this API was intended to do.
+				 * Things may go astray as a result.
+				 */
+				inner_op((void *)start, (void *)e);
+
+				/*
+				 * Now handle the L2 cache.
+				 */
+				phys = page_to_phys(page) + (start & ~PAGE_MASK);
+				outer_op(phys, phys + e - start);
+
+				put_page(page);
+			}
+			start = e;
+		} while (start < end && start < vma->vm_end);
+	} while (start < end);
+	up_read(&mm->mmap_sem);
+
+	return 0;
+}
+#endif