Remove unclear comment about address truncation in busdma. Add (hopefully much clearer) comment at declaration of PHYS_TO_VM_PAGE().

Noted by:	avg

5 files changed, 5 insertions, 20 deletions

diff --git a/sys/arm/arm/busdma_machdep-v6.c b/sys/arm/arm/busdma_machdep-v6.c
index a945b6371dc8..66d461204f16 100644
--- a/sys/arm/arm/busdma_machdep-v6.c
+++ b/sys/arm/arm/busdma_machdep-v6.c
@@ -1089,10 +1089,6 @@ _bus_dmamap_load_phys(bus_dma_tag_t dmat,
 				sl++;
 				sl->vaddr = 0;
 				sl->datacount = sgsize;
-				/*
-				 * PHYS_TO_VM_PAGE() will truncate
-				 * unaligned addresses.
-				 */
 				sl->pages = PHYS_TO_VM_PAGE(curaddr);
 				sl->dataoffs = curaddr & PAGE_MASK;
 			} else
@@ -1214,10 +1210,6 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat,
 				sl++;
 				sl->vaddr = kvaddr;
 				sl->datacount = sgsize;
-				/*
-				 * PHYS_TO_VM_PAGE() will truncate
-				 * unaligned addresses.
-				 */
 				sl->pages = PHYS_TO_VM_PAGE(curaddr);
 				sl->dataoffs = curaddr & PAGE_MASK;
 			} else
@@ -1687,7 +1679,6 @@ add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
 		bpage->busaddr |= addr & PAGE_MASK;
 	}
 	bpage->datavaddr = vaddr;
-	/* PHYS_TO_VM_PAGE() will truncate unaligned addresses. */
 	bpage->datapage = PHYS_TO_VM_PAGE(addr);
 	bpage->dataoffs = addr & PAGE_MASK;
 	bpage->datacount = size;
diff --git a/sys/arm/arm/busdma_machdep.c b/sys/arm/arm/busdma_machdep.c
index e7ec8b1403d7..00c7f2314f98 100644
--- a/sys/arm/arm/busdma_machdep.c
+++ b/sys/arm/arm/busdma_machdep.c
@@ -993,10 +993,6 @@ _bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
 				sl++;
 				sl->vaddr = 0;
 				sl->datacount = sgsize;
-				/*
-				 * PHYS_TO_VM_PAGE() will truncate
-				 * unaligned addresses.
-				 */
 				sl->pages = PHYS_TO_VM_PAGE(curaddr);
 				sl->dataoffs = curaddr & PAGE_MASK;
 			} else
@@ -1108,10 +1104,6 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
 				sl++;
 				sl->vaddr = kvaddr;
 				sl->datacount = sgsize;
-				/*
-				 * PHYS_TO_VM_PAGE() will truncate
-				 * unaligned addresses.
-				 */
 				sl->pages = PHYS_TO_VM_PAGE(curaddr);
 				sl->dataoffs = curaddr & PAGE_MASK;
 			} else
@@ -1541,7 +1533,6 @@ add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
 		bpage->busaddr |= addr & PAGE_MASK;
 	}
 	bpage->datavaddr = vaddr;
-	/* PHYS_TO_VM_PAGE() will truncate unaligned addresses. */
 	bpage->datapage = PHYS_TO_VM_PAGE(addr);
 	bpage->dataoffs = addr & PAGE_MASK;
 	bpage->datacount = size;
diff --git a/sys/arm64/arm64/busdma_bounce.c b/sys/arm64/arm64/busdma_bounce.c
index 1dc071db62be..cd0c087a0077 100644
--- a/sys/arm64/arm64/busdma_bounce.c
+++ b/sys/arm64/arm64/busdma_bounce.c
@@ -1009,7 +1009,6 @@ add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
 		bpage->busaddr |= addr & PAGE_MASK;
 	}
 	bpage->datavaddr = vaddr;
-	/* PHYS_TO_VM_PAGE() will truncate unaligned addresses. */
 	bpage->datapage = PHYS_TO_VM_PAGE(addr);
 	bpage->dataoffs = addr & PAGE_MASK;
 	bpage->datacount = size;
diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index dedd6ac9eb0c..3dbd7f7015ac 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -375,6 +375,11 @@ extern long first_page;			/* first physical page number */
 
 #define VM_PAGE_TO_PHYS(entry)	((entry)->phys_addr)
 
+/*
+ * PHYS_TO_VM_PAGE() Returns the vm_page_t object that represents a memory
+ * page to which the given physical address belongs. The correct vm_page_t
+ * object is returned for addresses that are not page-aligned.
+ */
 vm_page_t PHYS_TO_VM_PAGE(vm_paddr_t pa);
 
 /*
diff --git a/sys/x86/x86/busdma_bounce.c b/sys/x86/x86/busdma_bounce.c
index cac6c7158caa..ebd6238ef820 100644
--- a/sys/x86/x86/busdma_bounce.c
+++ b/sys/x86/x86/busdma_bounce.c
@@ -1006,7 +1006,6 @@ add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
 		bpage->busaddr |= addr & PAGE_MASK;
 	}
 	bpage->datavaddr = vaddr;
-	/* PHYS_TO_VM_PAGE() will truncate unaligned addresses. */
 	bpage->datapage = PHYS_TO_VM_PAGE(addr);
 	bpage->dataoffs = addr & PAGE_MASK;
 	bpage->datacount = size;