firewire: fw-ohci: Dynamically allocate buffers for DMA descriptors

Previously, the fw-ohci driver used fixed-length buffers for storing
descriptors for isochronous receive DMA programs.  If an application
(such as libdc1394) generated a DMA program that was too large, fw-ohci
would reach the limit of its fixed-sized buffer and return an error to
userspace.

This patch replaces the fixed-length ring-buffer with a linked-list of
page-sized buffers.  Additional buffers can be dynamically allocated and
appended to the list when necessary.  For a particular context, buffers
are kept around after use and reused as necessary, so there is no
allocation taking place after the DMA program is generated for the first
time.

In addition, the buffers it uses are coherent for DMA so there is no
syncing required before and after writes.  This syncing wasn't properly
done in the previous version of the code.

-

This is the fourth version of my patch that replaces a fixed-length
buffer for DMA descriptors with a dynamically allocated linked-list of
buffers.

As we discovered with the last attempt, new context programs are
sometimes queued from interrupt context, making it unacceptable to call
tasklet_disable() from context_get_descriptors().

This version of the patch uses ohci->lock for all locking needs instead
of tasklet_disable/enable.  There is a new requirement that
context_get_descriptors() be called while holding ohci->lock.  It was
already held for the AT context, so adding the requirement for the iso
context did not seem particularly onerous.  In addition, this has the
side benefit of allowing iso queue to be safely called from concurrent
user-space threads, which previously was not safe.
Signed-off-by: David Moore <dcm@acm.org>
Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Jarod Wilson <jwilson@redhat.com>

-

Fixes the following issues:
  - Isochronous reception stopped prematurely if an application used a
    larger buffer.  (Reproduced with coriander.)
  - Isochronous reception stopped after one or a few frames on VT630x
    in OHCI 1.0 mode.  (Fixes reception in coriander, but dvgrab still
    doesn't work with these chips.)

Patch update: struct member alignment, whitespace nits
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/fw-ohci.c

@@ -98,17 +98,48 @@ struct context;
 typedef int (*descriptor_callback_t)(struct context *ctx,
 				     struct descriptor *d,
 				     struct descriptor *last);
+
+/*
+ * A buffer that contains a block of DMA-able coherent memory used for
+ * storing a portion of a DMA descriptor program.
+ */
+struct descriptor_buffer {
+	struct list_head list;
+	dma_addr_t buffer_bus;
+	size_t buffer_size;
+	size_t used;
+	struct descriptor buffer[0];
+};
+
 struct context {
 	struct fw_ohci *ohci;
 	u32 regs;
+	int total_allocation;
 
-	struct descriptor *buffer;
-	dma_addr_t buffer_bus;
-	size_t buffer_size;
-	struct descriptor *head_descriptor;
-	struct descriptor *tail_descriptor;
-	struct descriptor *tail_descriptor_last;
-	struct descriptor *prev_descriptor;
+	/*
+	 * List of page-sized buffers for storing DMA descriptors.
+	 * Head of list contains buffers in use and tail of list contains
+	 * free buffers.
+	 */
+	struct list_head buffer_list;
+
+	/*
+	 * Pointer to a buffer inside buffer_list that contains the tail
+	 * end of the current DMA program.
+	 */
+	struct descriptor_buffer *buffer_tail;
+
+	/*
+	 * The descriptor containing the branch address of the first
+	 * descriptor that has not yet been filled by the device.
+	 */
+	struct descriptor *last;
+
+	/*
+	 * The last descriptor in the DMA program.  It contains the branch
+	 * address that must be updated upon appending a new descriptor.
+	 */
+	struct descriptor *prev;
 
 	descriptor_callback_t callback;
 
@@ -198,8 +229,6 @@ static inline struct fw_ohci *fw_ohci(struct fw_card *card)
 #define SELF_ID_BUF_SIZE		0x800
 #define OHCI_TCODE_PHY_PACKET		0x0e
 #define OHCI_VERSION_1_1		0x010010
-#define ISO_BUFFER_SIZE			(64 * 1024)
-#define AT_BUFFER_SIZE			4096
 
 static char ohci_driver_name[] = KBUILD_MODNAME;
 
@@ -456,71 +485,108 @@ find_branch_descriptor(struct descriptor *d, int z)
 static void context_tasklet(unsigned long data)
 {
 	struct context *ctx = (struct context *) data;
-	struct fw_ohci *ohci = ctx->ohci;
 	struct descriptor *d, *last;
 	u32 address;
 	int z;
+	struct descriptor_buffer *desc;
 
-	dma_sync_single_for_cpu(ohci->card.device, ctx->buffer_bus,
-				ctx->buffer_size, DMA_TO_DEVICE);
-
-	d    = ctx->tail_descriptor;
-	last = ctx->tail_descriptor_last;
-
+	desc = list_entry(ctx->buffer_list.next,
+			struct descriptor_buffer, list);
+	last = ctx->last;
 	while (last->branch_address != 0) {
+		struct descriptor_buffer *old_desc = desc;
 		address = le32_to_cpu(last->branch_address);
 		z = address & 0xf;
-		d = ctx->buffer + (address - ctx->buffer_bus) / sizeof(*d);
+		address &= ~0xf;
+
+		/* If the branch address points to a buffer outside of the
+		 * current buffer, advance to the next buffer. */
+		if (address < desc->buffer_bus ||
+				address >= desc->buffer_bus + desc->used)
+			desc = list_entry(desc->list.next,
+					struct descriptor_buffer, list);
+		d = desc->buffer + (address - desc->buffer_bus) / sizeof(*d);
 		last = find_branch_descriptor(d, z);
 
 		if (!ctx->callback(ctx, d, last))
 			break;
 
-		ctx->tail_descriptor      = d;
-		ctx->tail_descriptor_last = last;
+		if (old_desc != desc) {
+			/* If we've advanced to the next buffer, move the
+			 * previous buffer to the free list. */
+			unsigned long flags;
+			old_desc->used = 0;
+			spin_lock_irqsave(&ctx->ohci->lock, flags);
+			list_move_tail(&old_desc->list, &ctx->buffer_list);
+			spin_unlock_irqrestore(&ctx->ohci->lock, flags);
+		}
+		ctx->last = last;
 	}
 }
 
+/*
+ * Allocate a new buffer and add it to the list of free buffers for this
+ * context.  Must be called with ohci->lock held.
+ */
+static int
+context_add_buffer(struct context *ctx)
+{
+	struct descriptor_buffer *desc;
+	dma_addr_t bus_addr;
+	int offset;
+
+	/*
+	 * 16MB of descriptors should be far more than enough for any DMA
+	 * program.  This will catch run-away userspace or DoS attacks.
+	 */
+	if (ctx->total_allocation >= 16*1024*1024)
+		return -ENOMEM;
+
+	desc = dma_alloc_coherent(ctx->ohci->card.device, PAGE_SIZE,
+			&bus_addr, GFP_ATOMIC);
+	if (!desc)
+		return -ENOMEM;
+
+	offset = (void *)&desc->buffer - (void *)desc;
+	desc->buffer_size = PAGE_SIZE - offset;
+	desc->buffer_bus = bus_addr + offset;
+	desc->used = 0;
+
+	list_add_tail(&desc->list, &ctx->buffer_list);
+	ctx->total_allocation += PAGE_SIZE;
+
+	return 0;
+}
+
 static int
 context_init(struct context *ctx, struct fw_ohci *ohci,
-	     size_t buffer_size, u32 regs,
-	     descriptor_callback_t callback)
+	     u32 regs, descriptor_callback_t callback)
 {
 	ctx->ohci = ohci;
 	ctx->regs = regs;
-	ctx->buffer_size = buffer_size;
-	ctx->buffer = kmalloc(buffer_size, GFP_KERNEL);
-	if (ctx->buffer == NULL)
+	ctx->total_allocation = 0;
+
+	INIT_LIST_HEAD(&ctx->buffer_list);
+	if (context_add_buffer(ctx) < 0)
 		return -ENOMEM;
 
+	ctx->buffer_tail = list_entry(ctx->buffer_list.next,
+			struct descriptor_buffer, list);
+
 	tasklet_init(&ctx->tasklet, context_tasklet, (unsigned long)ctx);
 	ctx->callback = callback;
 
-	ctx->buffer_bus =
-		dma_map_single(ohci->card.device, ctx->buffer,
-			       buffer_size, DMA_TO_DEVICE);
-	if (dma_mapping_error(ctx->buffer_bus)) {
-		kfree(ctx->buffer);
-		return -ENOMEM;
-	}
-
-	ctx->head_descriptor      = ctx->buffer;
-	ctx->prev_descriptor      = ctx->buffer;
-	ctx->tail_descriptor      = ctx->buffer;
-	ctx->tail_descriptor_last = ctx->buffer;
-
 	/*
 	 * We put a dummy descriptor in the buffer that has a NULL
 	 * branch address and looks like it's been sent.  That way we
-	 * have a descriptor to append DMA programs to.  Also, the
-	 * ring buffer invariant is that it always has at least one
-	 * element so that head == tail means buffer full.
+	 * have a descriptor to append DMA programs to.
 	 */
-
-	memset(ctx->head_descriptor, 0, sizeof(*ctx->head_descriptor));
-	ctx->head_descriptor->control = cpu_to_le16(DESCRIPTOR_OUTPUT_LAST);
-	ctx->head_descriptor->transfer_status = cpu_to_le16(0x8011);
-	ctx->head_descriptor++;
+	memset(ctx->buffer_tail->buffer, 0, sizeof(*ctx->buffer_tail->buffer));
+	ctx->buffer_tail->buffer->control = cpu_to_le16(DESCRIPTOR_OUTPUT_LAST);
+	ctx->buffer_tail->buffer->transfer_status = cpu_to_le16(0x8011);
+	ctx->buffer_tail->used += sizeof(*ctx->buffer_tail->buffer);
+	ctx->last = ctx->buffer_tail->buffer;
+	ctx->prev = ctx->buffer_tail->buffer;
 
 	return 0;
 }
@@ -529,35 +595,42 @@ static void
 context_release(struct context *ctx)
 {
 	struct fw_card *card = &ctx->ohci->card;
+	struct descriptor_buffer *desc, *tmp;
 
-	dma_unmap_single(card->device, ctx->buffer_bus,
-			 ctx->buffer_size, DMA_TO_DEVICE);
-	kfree(ctx->buffer);
+	list_for_each_entry_safe(desc, tmp, &ctx->buffer_list, list)
+		dma_free_coherent(card->device, PAGE_SIZE, desc,
+			desc->buffer_bus -
+			((void *)&desc->buffer - (void *)desc));
 }
 
+/* Must be called with ohci->lock held */
 static struct descriptor *
 context_get_descriptors(struct context *ctx, int z, dma_addr_t *d_bus)
 {
-	struct descriptor *d, *tail, *end;
-
-	d = ctx->head_descriptor;
-	tail = ctx->tail_descriptor;
-	end = ctx->buffer + ctx->buffer_size / sizeof(*d);
-
-	if (d + z <= tail) {
-		goto has_space;
-	} else if (d > tail && d + z <= end) {
-		goto has_space;
-	} else if (d > tail && ctx->buffer + z <= tail) {
-		d = ctx->buffer;
-		goto has_space;
-	}
+	struct descriptor *d = NULL;
+	struct descriptor_buffer *desc = ctx->buffer_tail;
+
+	if (z * sizeof(*d) > desc->buffer_size)
+		return NULL;
+
+	if (z * sizeof(*d) > desc->buffer_size - desc->used) {
+		/* No room for the descriptor in this buffer, so advance to the
+		 * next one. */
 
-	return NULL;
+		if (desc->list.next == &ctx->buffer_list) {
+			/* If there is no free buffer next in the list,
+			 * allocate one. */
+			if (context_add_buffer(ctx) < 0)
+				return NULL;
+		}
+		desc = list_entry(desc->list.next,
+				struct descriptor_buffer, list);
+		ctx->buffer_tail = desc;
+	}
 
- has_space:
+	d = desc->buffer + desc->used / sizeof(*d);
 	memset(d, 0, z * sizeof(*d));
-	*d_bus = ctx->buffer_bus + (d - ctx->buffer) * sizeof(*d);
+	*d_bus = desc->buffer_bus + desc->used;
 
 	return d;
 }
@@ -567,7 +640,7 @@ static void context_run(struct context *ctx, u32 extra)
 	struct fw_ohci *ohci = ctx->ohci;
 
 	reg_write(ohci, COMMAND_PTR(ctx->regs),
-		  le32_to_cpu(ctx->tail_descriptor_last->branch_address));
+		  le32_to_cpu(ctx->last->branch_address));
 	reg_write(ohci, CONTROL_CLEAR(ctx->regs), ~0);
 	reg_write(ohci, CONTROL_SET(ctx->regs), CONTEXT_RUN | extra);
 	flush_writes(ohci);
@@ -577,15 +650,13 @@ static void context_append(struct context *ctx,
 			   struct descriptor *d, int z, int extra)
 {
 	dma_addr_t d_bus;
+	struct descriptor_buffer *desc = ctx->buffer_tail;
 
-	d_bus = ctx->buffer_bus + (d - ctx->buffer) * sizeof(*d);
+	d_bus = desc->buffer_bus + (d - desc->buffer) * sizeof(*d);
 
-	ctx->head_descriptor = d + z + extra;
-	ctx->prev_descriptor->branch_address = cpu_to_le32(d_bus | z);
-	ctx->prev_descriptor = find_branch_descriptor(d, z);
-
-	dma_sync_single_for_device(ctx->ohci->card.device, ctx->buffer_bus,
-				   ctx->buffer_size, DMA_TO_DEVICE);
+	desc->used += (z + extra) * sizeof(*d);
+	ctx->prev->branch_address = cpu_to_le32(d_bus | z);
+	ctx->prev = find_branch_descriptor(d, z);
 
 	reg_write(ctx->ohci, CONTROL_SET(ctx->regs), CONTEXT_WAKE);
 	flush_writes(ctx->ohci);
@@ -1571,8 +1642,7 @@ ohci_allocate_iso_context(struct fw_card *card, int type, size_t header_size)
 	if (ctx->header == NULL)
 		goto out;
 
-	retval = context_init(&ctx->context, ohci, ISO_BUFFER_SIZE,
-			      regs, callback);
+	retval = context_init(&ctx->context, ohci, regs, callback);
 	if (retval < 0)
 		goto out_with_header;
 
@@ -1933,16 +2003,22 @@ ohci_queue_iso(struct fw_iso_context *base,
 	       unsigned long payload)
 {
 	struct iso_context *ctx = container_of(base, struct iso_context, base);
+	unsigned long flags;
+	int retval;
 
+	spin_lock_irqsave(&ctx->context.ohci->lock, flags);
 	if (base->type == FW_ISO_CONTEXT_TRANSMIT)
-		return ohci_queue_iso_transmit(base, packet, buffer, payload);
+		retval = ohci_queue_iso_transmit(base, packet, buffer, payload);
 	else if (ctx->context.ohci->version >= OHCI_VERSION_1_1)
-		return ohci_queue_iso_receive_dualbuffer(base, packet,
+		retval = ohci_queue_iso_receive_dualbuffer(base, packet,
 							 buffer, payload);
 	else
-		return ohci_queue_iso_receive_packet_per_buffer(base, packet,
+		retval = ohci_queue_iso_receive_packet_per_buffer(base, packet,
 								buffer,
 								payload);
+	spin_unlock_irqrestore(&ctx->context.ohci->lock, flags);
+
+	return retval;
 }
 
 static const struct fw_card_driver ohci_driver = {
@@ -2014,10 +2090,10 @@ pci_probe(struct pci_dev *dev, const struct pci_device_id *ent)
 	ar_context_init(&ohci->ar_response_ctx, ohci,
 			OHCI1394_AsRspRcvContextControlSet);
 
-	context_init(&ohci->at_request_ctx, ohci, AT_BUFFER_SIZE,
+	context_init(&ohci->at_request_ctx, ohci,
 		     OHCI1394_AsReqTrContextControlSet, handle_at_packet);
 
-	context_init(&ohci->at_response_ctx, ohci, AT_BUFFER_SIZE,
+	context_init(&ohci->at_response_ctx, ohci,
 		     OHCI1394_AsRspTrContextControlSet, handle_at_packet);
 
 	reg_write(ohci, OHCI1394_IsoRecvIntMaskSet, ~0);