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Message-Id: <1337003229-9158-2-git-send-email-jiang.liu@huawei.com>
Date: Mon, 14 May 2012 21:47:03 +0800
From: Jiang Liu <liuj97@...il.com>
To: Dan Williams <dan.j.williams@...el.com>,
Maciej Sosnowski <maciej.sosnowski@...el.com>,
Vinod Koul <vinod.koul@...el.com>
Cc: Jiang Liu <jiang.liu@...wei.com>,
Keping Chen <chenkeping@...wei.com>,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
Jiang Liu <liuj97@...il.com>
Subject: [RFC PATCH v2 1/7] dmaengine: enhance DMA channel reference count management
From: Jiang Liu <jiang.liu@...wei.com>
Intel IOAT (Crystal Beach) devices are often built into PCIe root complex.
When hot-plugging a PCI root complex (IOH) on Intel Nehalem/Westmere
platforms, all IOAT devices built in the IOH must be handled first.
For future Intel processors with Integrated IOH (IIO), IOAT device will
get involved even when hot-plugging physical processors.
Currently dmaengine core already supports hot-add of IOAT devices,
but hot-removal of IOAT devices is still unsupported due to a design
limiation in the dmaengine core.
Currently dmaengine has an assumption that DMA devices could only be
deregistered when there's no any clients making use of DMA devices.
So dma_async_device_unregister() is designed to be called by DMA device
driver's module_exit routines only. But the ioatdma driver doesn't
conform to that rule, it calls dma_async_device_unregister() from its
driver detaching routine instead of module_exit routine.
This patch set enhances the dmaengine core to support DMA device hotplug,
so that dma_async_device_unregister() could be called by DMA driver's
detach routines to hot-remove DMA devices at runtime.
With currently implementation, variable dmaengine_ref_count is used to track
how many clients are making use of the dmaengine. There's also a per-channel
reference count named client_count in struct dma_chan. For successfully
initialized channels, dma_chan->client_count is set to dmaengine_ref_count.
That means all channels can't be released/removed if there are still clients.
To support DMA device hotplug, this patch change dma_chan->client_count to
track actual reference to the DMA channel instead of tracking the global
client count.
Signed-off-by: Jiang Liu <liuj97@...il.com>
---
drivers/dma/dmaengine.c | 193 ++++++++++++++++-------------------------------
1 file changed, 67 insertions(+), 126 deletions(-)
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 2397f6f..58bc45c 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -64,7 +64,7 @@
static DEFINE_MUTEX(dma_list_mutex);
static DEFINE_IDR(dma_idr);
static LIST_HEAD(dma_device_list);
-static long dmaengine_ref_count;
+static long dmaengine_client_count;
/* --- sysfs implementation --- */
@@ -168,8 +168,6 @@ static struct class dma_devclass = {
/* --- client and device registration --- */
-#define dma_device_satisfies_mask(device, mask) \
- __dma_device_satisfies_mask((device), &(mask))
static int
__dma_device_satisfies_mask(struct dma_device *device, dma_cap_mask_t *want)
{
@@ -186,22 +184,6 @@ static struct module *dma_chan_to_owner(struct dma_chan *chan)
}
/**
- * balance_ref_count - catch up the channel reference count
- * @chan - channel to balance ->client_count versus dmaengine_ref_count
- *
- * balance_ref_count must be called under dma_list_mutex
- */
-static void balance_ref_count(struct dma_chan *chan)
-{
- struct module *owner = dma_chan_to_owner(chan);
-
- while (chan->client_count < dmaengine_ref_count) {
- __module_get(owner);
- chan->client_count++;
- }
-}
-
-/**
* dma_chan_get - try to grab a dma channel's parent driver module
* @chan - channel to grab
*
@@ -209,28 +191,22 @@ static void balance_ref_count(struct dma_chan *chan)
*/
static int dma_chan_get(struct dma_chan *chan)
{
- int err = -ENODEV;
+ int err = 0;
struct module *owner = dma_chan_to_owner(chan);
- if (chan->client_count) {
- __module_get(owner);
- err = 0;
- } else if (try_module_get(owner))
- err = 0;
-
- if (err == 0)
- chan->client_count++;
+ /* Device driver module has been unloaded */
+ if (!try_module_get(owner))
+ return -ENODEV;
/* allocate upon first client reference */
- if (chan->client_count == 1 && err == 0) {
+ if (++chan->client_count == 1) {
int desc_cnt = chan->device->device_alloc_chan_resources(chan);
if (desc_cnt < 0) {
err = desc_cnt;
chan->client_count = 0;
module_put(owner);
- } else if (!dma_has_cap(DMA_PRIVATE, chan->device->cap_mask))
- balance_ref_count(chan);
+ }
}
return err;
@@ -244,12 +220,10 @@ static int dma_chan_get(struct dma_chan *chan)
*/
static void dma_chan_put(struct dma_chan *chan)
{
- if (!chan->client_count)
- return; /* this channel failed alloc_chan_resources */
- chan->client_count--;
- module_put(dma_chan_to_owner(chan));
- if (chan->client_count == 0)
+ BUG_ON(chan->client_count <= 0);
+ if (--chan->client_count == 0)
chan->device->device_free_chan_resources(chan);
+ module_put(dma_chan_to_owner(chan));
}
enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie)
@@ -278,9 +252,11 @@ 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
+ * @prev_chan - previous associated channel for this entry
*/
struct dma_chan_tbl_ent {
struct dma_chan *chan;
+ struct dma_chan *prev_chan;
};
/**
@@ -367,7 +343,7 @@ void dma_issue_pending_all(void)
EXPORT_SYMBOL(dma_issue_pending_all);
/**
- * nth_chan - returns the nth channel of the given capability
+ * nth_chan - grab a reference to the nth channel of the given capability
* @cap: capability to match
* @n: nth channel desired
*
@@ -387,17 +363,19 @@ static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
dma_has_cap(DMA_PRIVATE, device->cap_mask))
continue;
list_for_each_entry(chan, &device->channels, device_node) {
- if (!chan->client_count)
+ if (dma_chan_get(chan))
continue;
- if (!min)
- min = chan;
- else if (chan->table_count < min->table_count)
- min = chan;
-
if (n-- == 0) {
ret = chan;
break; /* done */
}
+ if (!min)
+ min = chan;
+ else if (chan->table_count < min->table_count) {
+ dma_chan_put(min);
+ min = chan;
+ } else
+ dma_chan_put(chan);
}
if (ret)
break; /* done */
@@ -405,6 +383,8 @@ static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
if (!ret)
ret = min;
+ else if (min)
+ dma_chan_put(min);
if (ret)
ret->table_count++;
@@ -423,37 +403,39 @@ static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
static void dma_channel_rebalance(void)
{
struct dma_chan *chan;
- struct dma_device *device;
+ struct dma_chan_tbl_ent *entry;
int cpu;
int cap;
- int n;
+ int n = 0;
- /* undo the last distribution */
+ /* save 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) {
- if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
- continue;
- list_for_each_entry(chan, &device->channels, device_node)
- chan->table_count = 0;
- }
+ for_each_possible_cpu(cpu) {
+ entry = per_cpu_ptr(channel_table[cap], cpu);
+ entry->prev_chan = entry->chan;
+ entry->chan = NULL;
+ if (entry->prev_chan)
+ entry->prev_chan->table_count--;
+ }
- /* don't populate the channel_table if no clients are available */
- if (!dmaengine_ref_count)
- return;
+ /* redistribute available channels if there are clients */
+ if (dmaengine_client_count)
+ 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);
+ entry = per_cpu_ptr(channel_table[cap], cpu);
+ entry->chan = chan;
+ }
- /* redistribute available channels */
- n = 0;
+ /* undo the last distribution */
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;
+ for_each_possible_cpu(cpu) {
+ chan = per_cpu(channel_table[cap]->prev_chan, cpu);
+ if (chan)
+ dma_chan_put(chan);
}
}
@@ -511,19 +493,16 @@ struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, v
chan = private_candidate(mask, device, fn, fn_param);
if (chan) {
/* Found a suitable channel, try to grab, prep, and
- * return it. We first set DMA_PRIVATE to disable
- * balance_ref_count as this channel will not be
- * published in the general-purpose allocator
+ * return it.
*/
dma_cap_set(DMA_PRIVATE, device->cap_mask);
device->privatecnt++;
err = dma_chan_get(chan);
- if (err == -ENODEV) {
+ if (err == -ENODEV)
pr_debug("%s: %s module removed\n", __func__,
dma_chan_name(chan));
- list_del_rcu(&device->global_node);
- } else if (err)
+ else if (err)
pr_debug("%s: failed to get %s: (%d)\n",
__func__, dma_chan_name(chan), err);
else
@@ -560,57 +539,26 @@ EXPORT_SYMBOL_GPL(dma_release_channel);
*/
void dmaengine_get(void)
{
- struct dma_device *device, *_d;
- struct dma_chan *chan;
- int err;
-
mutex_lock(&dma_list_mutex);
- dmaengine_ref_count++;
-
- /* try to grab channels */
- list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
- if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
- continue;
- list_for_each_entry(chan, &device->channels, device_node) {
- err = dma_chan_get(chan);
- if (err == -ENODEV) {
- /* module removed before we could use it */
- list_del_rcu(&device->global_node);
- break;
- } else if (err)
- pr_err("%s: failed to get %s: (%d)\n",
- __func__, dma_chan_name(chan), 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)
+ if (++dmaengine_client_count == 1)
dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dmaengine_get);
/**
- * dmaengine_put - let dma drivers be removed when ref_count == 0
+ * dmaengine_put - deregister interest in dma_channels
*/
void dmaengine_put(void)
{
- struct dma_device *device;
- struct dma_chan *chan;
-
mutex_lock(&dma_list_mutex);
- dmaengine_ref_count--;
- BUG_ON(dmaengine_ref_count < 0);
- /* drop channel references */
- list_for_each_entry(device, &dma_device_list, global_node) {
- if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
- continue;
- list_for_each_entry(chan, &device->channels, device_node)
- dma_chan_put(chan);
- }
+ BUG_ON(dmaengine_client_count <= 0);
+ if (--dmaengine_client_count == 0)
+ dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dmaengine_put);
@@ -773,26 +721,11 @@ int dma_async_device_register(struct dma_device *device)
device->chancnt = chancnt;
mutex_lock(&dma_list_mutex);
- /* take references on public channels */
- if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask))
- list_for_each_entry(chan, &device->channels, device_node) {
- /* if clients are already waiting for channels we need
- * to take references on their behalf
- */
- if (dma_chan_get(chan) == -ENODEV) {
- /* note we can only get here for the first
- * channel as the remaining channels are
- * guaranteed to get a reference
- */
- rc = -ENODEV;
- mutex_unlock(&dma_list_mutex);
- goto err_out;
- }
- }
list_add_tail_rcu(&device->global_node, &dma_device_list);
if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
device->privatecnt++; /* Always private */
- dma_channel_rebalance();
+ else
+ dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
return 0;
@@ -836,6 +769,14 @@ void dma_async_device_unregister(struct dma_device *device)
dma_channel_rebalance();
mutex_unlock(&dma_list_mutex);
+ /* Check whether it's called from module exit function. */
+ if (try_module_get(device->dev->driver->owner)) {
+ dev_warn(device->dev,
+ "%s isn't called from module exit function.\n",
+ __func__);
+ module_put(device->dev->driver->owner);
+ }
+
list_for_each_entry(chan, &device->channels, device_node) {
WARN_ONCE(chan->client_count,
"%s called while %d clients hold a reference\n",
--
1.7.9.5
--
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