dmaengine: centralize channel allocation, introduce dma_find_channel
Allowing multiple clients to each define their own channel allocation
scheme quickly leads to a pathological situation. For memory-to-memory
offload all clients can share a central allocator.
This simply moves the existing async_tx allocator to dmaengine with
minimal fixups:
* async_tx.c:get_chan_ref_by_cap --> dmaengine.c:nth_chan
* async_tx.c:async_tx_rebalance --> dmaengine.c:dma_channel_rebalance
* split out common code from async_tx.c:__async_tx_find_channel -->
dma_find_channel
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index d4d9259..87a8cd4 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -295,6 +295,164 @@
}
/**
+ * dma_cap_mask_all - enable iteration over all operation types
+ */
+static dma_cap_mask_t dma_cap_mask_all;
+
+/**
+ * dma_chan_tbl_ent - tracks channel allocations per core/operation
+ * @chan - associated channel for this entry
+ */
+struct dma_chan_tbl_ent {
+ struct dma_chan *chan;
+};
+
+/**
+ * channel_table - percpu lookup table for memory-to-memory offload providers
+ */
+static struct dma_chan_tbl_ent *channel_table[DMA_TX_TYPE_END];
+
+static int __init dma_channel_table_init(void)
+{
+ enum dma_transaction_type cap;
+ int err = 0;
+
+ bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);
+
+ /* 'interrupt' and 'slave' are channel capabilities, but are not
+ * associated with an operation so they do not need an entry in the
+ * channel_table
+ */
+ clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);
+ clear_bit(DMA_SLAVE, dma_cap_mask_all.bits);
+
+ for_each_dma_cap_mask(cap, dma_cap_mask_all) {
+ channel_table[cap] = alloc_percpu(struct dma_chan_tbl_ent);
+ if (!channel_table[cap]) {
+ err = -ENOMEM;
+ break;
+ }
+ }
+
+ if (err) {
+ pr_err("dmaengine: initialization failure\n");
+ for_each_dma_cap_mask(cap, dma_cap_mask_all)
+ if (channel_table[cap])
+ free_percpu(channel_table[cap]);
+ }
+
+ return err;
+}
+subsys_initcall(dma_channel_table_init);
+
+/**
+ * dma_find_channel - find a channel to carry out the operation
+ * @tx_type: transaction type
+ */
+struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
+{
+ struct dma_chan *chan;
+ int cpu;
+
+ WARN_ONCE(dmaengine_ref_count == 0,
+ "client called %s without a reference", __func__);
+
+ cpu = get_cpu();
+ chan = per_cpu_ptr(channel_table[tx_type], cpu)->chan;
+ put_cpu();
+
+ return chan;
+}
+EXPORT_SYMBOL(dma_find_channel);
+
+/**
+ * nth_chan - returns the nth channel of the given capability
+ * @cap: capability to match
+ * @n: nth channel desired
+ *
+ * Defaults to returning the channel with the desired capability and the
+ * lowest reference count when 'n' cannot be satisfied. Must be called
+ * under dma_list_mutex.
+ */
+static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
+{
+ struct dma_device *device;
+ struct dma_chan *chan;
+ struct dma_chan *ret = NULL;
+ struct dma_chan *min = NULL;
+
+ list_for_each_entry(device, &dma_device_list, global_node) {
+ if (!dma_has_cap(cap, device->cap_mask))
+ continue;
+ list_for_each_entry(chan, &device->channels, device_node) {
+ if (!chan->client_count)
+ continue;
+ if (!min)
+ min = chan;
+ else if (chan->table_count < min->table_count)
+ min = chan;
+
+ if (n-- == 0) {
+ ret = chan;
+ break; /* done */
+ }
+ }
+ if (ret)
+ break; /* done */
+ }
+
+ if (!ret)
+ ret = min;
+
+ if (ret)
+ ret->table_count++;
+
+ return ret;
+}
+
+/**
+ * dma_channel_rebalance - redistribute the available channels
+ *
+ * Optimize for cpu isolation (each cpu gets a dedicated channel for an
+ * operation type) in the SMP case, and operation isolation (avoid
+ * multi-tasking channels) in the non-SMP case. Must be called under
+ * dma_list_mutex.
+ */
+static void dma_channel_rebalance(void)
+{
+ struct dma_chan *chan;
+ struct dma_device *device;
+ int cpu;
+ int cap;
+ int n;
+
+ /* undo the last distribution */
+ for_each_dma_cap_mask(cap, dma_cap_mask_all)
+ for_each_possible_cpu(cpu)
+ per_cpu_ptr(channel_table[cap], cpu)->chan = NULL;
+
+ list_for_each_entry(device, &dma_device_list, global_node)
+ list_for_each_entry(chan, &device->channels, device_node)
+ chan->table_count = 0;
+
+ /* don't populate the channel_table if no clients are available */
+ if (!dmaengine_ref_count)
+ return;
+
+ /* redistribute available channels */
+ n = 0;
+ for_each_dma_cap_mask(cap, dma_cap_mask_all)
+ for_each_online_cpu(cpu) {
+ if (num_possible_cpus() > 1)
+ chan = nth_chan(cap, n++);
+ else
+ chan = nth_chan(cap, -1);
+
+ per_cpu_ptr(channel_table[cap], cpu)->chan = chan;
+ }
+}
+
+/**
* dma_chans_notify_available - broadcast available channels to the clients
*/
static void dma_clients_notify_available(void)
@@ -339,7 +497,12 @@
dev_name(&chan->dev), err);
}
-
+ /* if this is the first reference and there were channels
+ * waiting we need to rebalance to get those channels
+ * incorporated into the channel table
+ */
+ if (dmaengine_ref_count == 1)
+ dma_channel_rebalance();
list_add_tail(&client->global_node, &dma_client_list);
mutex_unlock(&dma_list_mutex);
}
@@ -473,6 +636,7 @@
}
}
list_add_tail(&device->global_node, &dma_device_list);
+ dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
dma_clients_notify_available();
@@ -514,6 +678,7 @@
mutex_lock(&dma_list_mutex);
list_del(&device->global_node);
+ dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
list_for_each_entry(chan, &device->channels, device_node) {
@@ -768,3 +933,4 @@
}
subsys_initcall(dma_bus_init);
+