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dmaengine: centralize channel allocation, introduce dma_find_channel

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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>
This commit is contained in:
Dan Williams
2009-01-06 11:38:14 -07:00
parent 6f49a57aa5
commit bec085134e
3 changed files with 174 additions and 143 deletions
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168
drivers/dma/dmaengine.c
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@@ -294,6 +294,164 @@ static void dma_chan_release(struct dma_chan *chan)
call_rcu(&chan->rcu, dma_chan_free_rcu);
}
/**
* 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
*/
@@ -339,7 +497,12 @@ void dma_async_client_register(struct dma_client *client)
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 @@ int dma_async_device_register(struct dma_device *device)
}
}
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 @@ void dma_async_device_unregister(struct dma_device *device)
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 @@ static int __init dma_bus_init(void)
}
subsys_initcall(dma_bus_init);