Wrapper API for static bus_dma allocations
John Baldwin
jhb at freebsd.org
Thu Jan 29 21:04:23 UTC 2015
The bus_dma API to allocate a chunk of static DMA'able memory (e.g. for
descriptor rings) can be a bit obtuse to use in that it require a bit of
boilerplate to create a tag, allocate memory for the tag, then load it to get
the bus address. Similarly, freeing it also requires several steps. In
addition, some of the steps are a bit subtle (e.g. the need to check for an
error in the bus_dma callback instead of from bus_dmamap_load()) and not all
drivers get those correct.
To try to make this simpler I've written a little wrapper API that tries to
provide a single call to allocate a buffer and a single call to free a buffer.
Each buffer is described by a structure defined by the API, and if the call to
allocate a buffer succeeds, the structure contains both a pointer to the
buffer in the kernel's address space as well as a bus address of the buffer.
In the interests of simplicity, this API does not allow the buffer to be quite
as fully configured as the underlying bus_dma API, instead it aims to handle
the most common cases that are used in most drivers. As such, it assumes that
the buffer must be one contiguous range of DMA address space, and the only
parameters that can be specified are the parent tag, the alignment of the
buffer, the lowaddr parameter, the size of the buffer to allocate, and the
flags parameter that is normally passed to bus_dmamem_alloc(). I believe that
this should be sufficient to cover the vast majority of the drivers in our
tree.
I've included below a patch that contains the wrapper API along with a sample
conversion of the ndis driver (chosen at random). If folks like this idea I
will update the patch to include manpage changes as well.
--- //depot/vendor/freebsd/src/sys/compat/ndis/subr_ndis.c
+++ //depot/user/jhb/cleanup/sys/compat/ndis/subr_ndis.c
@@ -186,7 +186,6 @@
static ndis_status NdisMAllocateMapRegisters(ndis_handle,
uint32_t, uint8_t, uint32_t, uint32_t);
static void NdisMFreeMapRegisters(ndis_handle);
-static void ndis_mapshared_cb(void *, bus_dma_segment_t *, int, int);
static void NdisMAllocateSharedMemory(ndis_handle, uint32_t,
uint8_t, void **, ndis_physaddr *);
static void ndis_asyncmem_complete(device_object *, void *);
@@ -1387,23 +1386,6 @@
bus_dma_tag_destroy(sc->ndis_mtag);
}
-static void
-ndis_mapshared_cb(arg, segs, nseg, error)
- void *arg;
- bus_dma_segment_t *segs;
- int nseg;
- int error;
-{
- ndis_physaddr *p;
-
- if (error || nseg > 1)
- return;
-
- p = arg;
-
- p->np_quad = segs[0].ds_addr;
-}
-
/*
* This maps to bus_dmamem_alloc().
*/
@@ -1443,35 +1425,17 @@
* than 1GB of physical memory.
*/
- error = bus_dma_tag_create(sc->ndis_parent_tag, 64,
- 0, NDIS_BUS_SPACE_SHARED_MAXADDR, BUS_SPACE_MAXADDR, NULL,
- NULL, len, 1, len, BUS_DMA_ALLOCNOW, NULL, NULL,
- &sh->ndis_stag);
+ error = bus_dma_mem_create(&sh->ndis_mem, sc->ndis_parent_tag, 64,
+ NDIS_BUS_SPACE_SHARED_MAXADDR, len, BUS_DMA_NOWAIT | BUS_DMA_ZERO);
if (error) {
free(sh, M_DEVBUF);
return;
}
- error = bus_dmamem_alloc(sh->ndis_stag, vaddr,
- BUS_DMA_NOWAIT | BUS_DMA_ZERO, &sh->ndis_smap);
-
- if (error) {
- bus_dma_tag_destroy(sh->ndis_stag);
- free(sh, M_DEVBUF);
- return;
- }
+ *vaddr = sh->ndis_mem.dma_vaddr;
+ paddr->np_quad = sh->ndis_mem.dma_baddr;
- error = bus_dmamap_load(sh->ndis_stag, sh->ndis_smap, *vaddr,
- len, ndis_mapshared_cb, (void *)paddr, BUS_DMA_NOWAIT);
-
- if (error) {
- bus_dmamem_free(sh->ndis_stag, *vaddr, sh->ndis_smap);
- bus_dma_tag_destroy(sh->ndis_stag);
- free(sh, M_DEVBUF);
- return;
- }
-
/*
* Save the physical address along with the source address.
* The AirGo MIMO driver will call NdisMFreeSharedMemory()
@@ -1482,8 +1446,6 @@
*/
NDIS_LOCK(sc);
- sh->ndis_paddr.np_quad = paddr->np_quad;
- sh->ndis_saddr = *vaddr;
InsertHeadList((&sc->ndis_shlist), (&sh->ndis_list));
NDIS_UNLOCK(sc);
}
@@ -1581,13 +1543,13 @@
l = sc->ndis_shlist.nle_flink;
while (l != &sc->ndis_shlist) {
sh = CONTAINING_RECORD(l, struct ndis_shmem, ndis_list);
- if (sh->ndis_saddr == vaddr)
+ if (sh->ndis_mem.dma_vaddr == vaddr)
break;
/*
* Check the physaddr too, just in case the driver lied
* about the virtual address.
*/
- if (sh->ndis_paddr.np_quad == paddr.np_quad)
+ if (sh->ndis_mem.dma_baddr == paddr.np_quad)
break;
l = l->nle_flink;
}
@@ -1604,9 +1566,7 @@
NDIS_UNLOCK(sc);
- bus_dmamap_unload(sh->ndis_stag, sh->ndis_smap);
- bus_dmamem_free(sh->ndis_stag, sh->ndis_saddr, sh->ndis_smap);
- bus_dma_tag_destroy(sh->ndis_stag);
+ bus_dma_mem_free(&sh->ndis_mem);
free(sh, M_DEVBUF);
}
--- //depot/vendor/freebsd/src/sys/dev/if_ndis/if_ndisvar.h
+++ //depot/user/jhb/cleanup/sys/dev/if_ndis/if_ndisvar.h
@@ -66,10 +66,7 @@
struct ndis_shmem {
list_entry ndis_list;
- bus_dma_tag_t ndis_stag;
- bus_dmamap_t ndis_smap;
- void *ndis_saddr;
- ndis_physaddr ndis_paddr;
+ struct bus_dmamem ndis_mem;
};
struct ndis_cfglist {
--- //depot/vendor/freebsd/src/sys/kern/subr_bus_dma.c
+++ //depot/user/jhb/cleanup/sys/kern/subr_bus_dma.c
@@ -540,3 +540,66 @@
return (0);
}
+
+struct bus_dma_mem_cb_data {
+ struct bus_dmamem *mem;
+ int error;
+};
+
+static void
+bus_dma_mem_cb(void *arg, bus_dma_segment_t *segs, int nseg, int error)
+{
+ struct bus_dma_mem_cb_data *d;
+
+ d = arg;
+ d->error = error;
+ if (error)
+ return;
+ d->mem->dma_baddr = segs[0].ds_addr;
+}
+
+int
+bus_dma_mem_create(struct bus_dmamem *mem, bus_dma_tag_t parent,
+ bus_size_t alignment, bus_addr_t lowaddr, bus_size_t len, int flags)
+{
+ struct bus_dma_mem_cb_data d;
+ int error;
+
+ bzero(mem, sizeof(*mem));
+ error = bus_dma_tag_create(parent, alignment, 0, lowaddr,
+ BUS_SPACE_MAXADDR, NULL, NULL, len, 1, len, 0, NULL, NULL,
+ &mem->dma_tag);
+ if (error) {
+ bus_dma_mem_free(mem);
+ return (error);
+ }
+ error = bus_dmamem_alloc(mem->dma_tag, &mem->dma_vaddr, flags,
+ &mem->dma_map);
+ if (error) {
+ bus_dma_mem_free(mem);
+ return (error);
+ }
+ d.mem = mem;
+ error = bus_dmamap_load(mem->dma_tag, mem->dma_map, mem->dma_vaddr, len,
+ bus_dma_mem_cb, &d, BUS_DMA_NOWAIT);
+ if (error == 0)
+ error = d.error;
+ if (error) {
+ bus_dma_mem_free(mem);
+ return (error);
+ }
+ return (0);
+}
+
+void
+bus_dma_mem_free(struct bus_dmamem *mem)
+{
+
+ if (mem->dma_baddr != 0)
+ bus_dmamap_unload(mem->dma_tag, mem->dma_map);
+ if (mem->dma_vaddr != NULL)
+ bus_dmamem_free(mem->dma_tag, mem->dma_vaddr, mem->dma_map);
+ if (mem->dma_tag != NULL)
+ bus_dma_tag_destroy(mem->dma_tag);
+ bzero(mem, sizeof(*mem));
+}
--- //depot/vendor/freebsd/src/sys/sys/bus_dma.h
+++ //depot/user/jhb/cleanup/sys/sys/bus_dma.h
@@ -337,4 +337,29 @@
#endif /* __sparc64__ */
+/*
+ * A wrapper API to simplify management of static mappings.
+ */
+
+struct bus_dmamem {
+ bus_dma_tag_t dma_tag;
+ bus_dmamap_t dma_map;
+ void *dma_vaddr;
+ bus_addr_t dma_baddr;
+};
+
+/*
+ * Allocate a mapping. On success, zero is returned and the 'dma_vaddr'
+ * and 'dma_baddr' fields are populated with the virtual and bus addresses,
+ * respectively, of the mapping.
+ */
+int bus_dma_mem_create(struct bus_dmamem *mem, bus_dma_tag_t parent,
+ bus_size_t alignment, bus_addr_t lowaddr,
+ bus_size_t len, int flags);
+
+/*
+ * Release a mapping created by bus_dma_mem_create().
+ */
+void bus_dma_mem_free(struct bus_dmamem *mem);
+
#endif /* _BUS_DMA_H_ */
--
John Baldwin
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