gpu: host1x: Refactor channel allocation code

This is largely a rewrite of the Host1x channel allocation code, bringing
several changes:

- The previous code could deadlock due to an interaction
  between the 'reflock' mutex and CDMA timeout handling.
  This gets rid of the mutex.
- Support for more than 32 channels, required for Tegra186
- General refactoring, including better encapsulation
  of channel ownership handling into channel.c

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/gr2d.c

@@ -38,7 +38,7 @@ static int gr2d_init(struct host1x_client *client)
 
 	client->syncpts[0] = host1x_syncpt_request(client->dev, flags);
 	if (!client->syncpts[0]) {
-		host1x_channel_free(gr2d->channel);
+		host1x_channel_put(gr2d->channel);
 		return -ENOMEM;
 	}
 
@@ -57,7 +57,7 @@ static int gr2d_exit(struct host1x_client *client)
 		return err;
 
 	host1x_syncpt_free(client->syncpts[0]);
-	host1x_channel_free(gr2d->channel);
+	host1x_channel_put(gr2d->channel);
 
 	return 0;
 }

drivers/gpu/drm/tegra/gr3d.c

@@ -48,7 +48,7 @@ static int gr3d_init(struct host1x_client *client)
 
 	client->syncpts[0] = host1x_syncpt_request(client->dev, flags);
 	if (!client->syncpts[0]) {
-		host1x_channel_free(gr3d->channel);
+		host1x_channel_put(gr3d->channel);
 		return -ENOMEM;
 	}
 
@@ -67,7 +67,7 @@ static int gr3d_exit(struct host1x_client *client)
 		return err;
 
 	host1x_syncpt_free(client->syncpts[0]);
-	host1x_channel_free(gr3d->channel);
+	host1x_channel_put(gr3d->channel);
 
 	return 0;
 }

drivers/gpu/drm/tegra/vic.c

@@ -182,7 +182,7 @@ static int vic_init(struct host1x_client *client)
 free_syncpt:
 	host1x_syncpt_free(client->syncpts[0]);
 free_channel:
-	host1x_channel_free(vic->channel);
+	host1x_channel_put(vic->channel);
 detach_device:
 	if (tegra->domain)
 		iommu_detach_device(tegra->domain, vic->dev);
@@ -203,7 +203,7 @@ static int vic_exit(struct host1x_client *client)
 		return err;
 
 	host1x_syncpt_free(client->syncpts[0]);
-	host1x_channel_free(vic->channel);
+	host1x_channel_put(vic->channel);
 
 	if (vic->domain) {
 		iommu_detach_device(vic->domain, vic->dev);

drivers/gpu/host1x/channel.c

@@ -24,19 +24,33 @@
 #include "job.h"
 
 /* Constructor for the host1x device list */
-int host1x_channel_list_init(struct host1x *host)
+int host1x_channel_list_init(struct host1x_channel_list *chlist,
+			     unsigned int num_channels)
 {
-	INIT_LIST_HEAD(&host->chlist.list);
-	mutex_init(&host->chlist_mutex);
-
-	if (host->info->nb_channels > BITS_PER_LONG) {
-		WARN(1, "host1x hardware has more channels than supported by the driver\n");
-		return -ENOSYS;
+	chlist->channels = kcalloc(num_channels, sizeof(struct host1x_channel),
+				   GFP_KERNEL);
+	if (!chlist->channels)
+		return -ENOMEM;
+
+	chlist->allocated_channels =
+		kcalloc(BITS_TO_LONGS(num_channels), sizeof(unsigned long),
+			GFP_KERNEL);
+	if (!chlist->allocated_channels) {
+		kfree(chlist->channels);
+		return -ENOMEM;
 	}
 
+	bitmap_zero(chlist->allocated_channels, num_channels);
+
 	return 0;
 }
 
+void host1x_channel_list_free(struct host1x_channel_list *chlist)
+{
+	kfree(chlist->allocated_channels);
+	kfree(chlist->channels);
+}
+
 int host1x_job_submit(struct host1x_job *job)
 {
 	struct host1x *host = dev_get_drvdata(job->channel->dev->parent);
@@ -47,86 +61,107 @@ EXPORT_SYMBOL(host1x_job_submit);
 
 struct host1x_channel *host1x_channel_get(struct host1x_channel *channel)
 {
-	int err = 0;
+	kref_get(&channel->refcount);
 
-	mutex_lock(&channel->reflock);
+	return channel;
+}
+EXPORT_SYMBOL(host1x_channel_get);
 
-	if (channel->refcount == 0)
-		err = host1x_cdma_init(&channel->cdma);
+/**
+ * host1x_channel_get_index() - Attempt to get channel reference by index
+ * @host: Host1x device object
+ * @index: Index of channel
+ *
+ * If channel number @index is currently allocated, increase its refcount
+ * and return a pointer to it. Otherwise, return NULL.
+ */
+struct host1x_channel *host1x_channel_get_index(struct host1x *host,
+						unsigned int index)
+{
+	struct host1x_channel *ch = &host->channel_list.channels[index];
 
-	if (!err)
-		channel->refcount++;
+	if (!kref_get_unless_zero(&ch->refcount))
+		return NULL;
 
-	mutex_unlock(&channel->reflock);
+	return ch;
+}
+
+static void release_channel(struct kref *kref)
+{
+	struct host1x_channel *channel =
+		container_of(kref, struct host1x_channel, refcount);
+	struct host1x *host = dev_get_drvdata(channel->dev->parent);
+	struct host1x_channel_list *chlist = &host->channel_list;
+
+	host1x_hw_cdma_stop(host, &channel->cdma);
+	host1x_cdma_deinit(&channel->cdma);
 
-	return err ? NULL : channel;
+	clear_bit(channel->id, chlist->allocated_channels);
 }
-EXPORT_SYMBOL(host1x_channel_get);
 
 void host1x_channel_put(struct host1x_channel *channel)
 {
-	mutex_lock(&channel->reflock);
+	kref_put(&channel->refcount, release_channel);
+}
+EXPORT_SYMBOL(host1x_channel_put);
 
-	if (channel->refcount == 1) {
-		struct host1x *host = dev_get_drvdata(channel->dev->parent);
+static struct host1x_channel *acquire_unused_channel(struct host1x *host)
+{
+	struct host1x_channel_list *chlist = &host->channel_list;
+	unsigned int max_channels = host->info->nb_channels;
+	unsigned int index;
 
-		host1x_hw_cdma_stop(host, &channel->cdma);
-		host1x_cdma_deinit(&channel->cdma);
+	index = find_first_zero_bit(chlist->allocated_channels, max_channels);
+	if (index >= max_channels) {
+		dev_err(host->dev, "failed to find free channel\n");
+		return NULL;
 	}
 
-	channel->refcount--;
+	chlist->channels[index].id = index;
 
-	mutex_unlock(&channel->reflock);
+	set_bit(index, chlist->allocated_channels);
+
+	return &chlist->channels[index];
 }
-EXPORT_SYMBOL(host1x_channel_put);
 
+/**
+ * host1x_channel_request() - Allocate a channel
+ * @device: Host1x unit this channel will be used to send commands to
+ *
+ * Allocates a new host1x channel for @device. If there are no free channels,
+ * this will sleep until one becomes available. May return NULL if CDMA
+ * initialization fails.
+ */
 struct host1x_channel *host1x_channel_request(struct device *dev)
 {
 	struct host1x *host = dev_get_drvdata(dev->parent);
-	unsigned int max_channels = host->info->nb_channels;
-	struct host1x_channel *channel = NULL;
-	unsigned long index;
+	struct host1x_channel_list *chlist = &host->channel_list;
+	struct host1x_channel *channel;
 	int err;
 
-	mutex_lock(&host->chlist_mutex);
+	channel = acquire_unused_channel(host);
+	if (!channel)
+		return NULL;
 
-	index = find_first_zero_bit(&host->allocated_channels, max_channels);
-	if (index >= max_channels)
-		goto fail;
+	kref_init(&channel->refcount);
+	mutex_init(&channel->submitlock);
+	channel->dev = dev;
 
-	channel = kzalloc(sizeof(*channel), GFP_KERNEL);
-	if (!channel)
+	err = host1x_hw_channel_init(host, channel, channel->id);
+	if (err < 0)
 		goto fail;
 
-	err = host1x_hw_channel_init(host, channel, index);
+	err = host1x_cdma_init(&channel->cdma);
 	if (err < 0)
 		goto fail;
 
-	/* Link device to host1x_channel */
-	channel->dev = dev;
-
-	/* Add to channel list */
-	list_add_tail(&channel->list, &host->chlist.list);
-
-	host->allocated_channels |= BIT(index);
-
-	mutex_unlock(&host->chlist_mutex);
 	return channel;
 
 fail:
-	dev_err(dev, "failed to init channel\n");
-	kfree(channel);
-	mutex_unlock(&host->chlist_mutex);
-	return NULL;
-}
-EXPORT_SYMBOL(host1x_channel_request);
+	clear_bit(channel->id, chlist->allocated_channels);
 
-void host1x_channel_free(struct host1x_channel *channel)
-{
-	struct host1x *host = dev_get_drvdata(channel->dev->parent);
+	dev_err(dev, "failed to initialize channel\n");
 
-	host->allocated_channels &= ~BIT(channel->id);
-	list_del(&channel->list);
-	kfree(channel);
+	return NULL;
 }
-EXPORT_SYMBOL(host1x_channel_free);
+EXPORT_SYMBOL(host1x_channel_request);

drivers/gpu/host1x/channel.h

@@ -20,27 +20,32 @@
 #define __HOST1X_CHANNEL_H
 
 #include <linux/io.h>
+#include <linux/kref.h>
 
 #include "cdma.h"
 
 struct host1x;
+struct host1x_channel;
 
-struct host1x_channel {
-	struct list_head list;
+struct host1x_channel_list {
+	struct host1x_channel *channels;
+	unsigned long *allocated_channels;
+};
 
-	unsigned int refcount;
+struct host1x_channel {
+	struct kref refcount;
 	unsigned int id;
-	struct mutex reflock;
 	struct mutex submitlock;
 	void __iomem *regs;
 	struct device *dev;
 	struct host1x_cdma cdma;
 };
 
 /* channel list operations */
-int host1x_channel_list_init(struct host1x *host);
-
-#define host1x_for_each_channel(host, channel)				\
-	list_for_each_entry(channel, &host->chlist.list, list)
+int host1x_channel_list_init(struct host1x_channel_list *chlist,
+			     unsigned int num_channels);
+void host1x_channel_list_free(struct host1x_channel_list *chlist);
+struct host1x_channel *host1x_channel_get_index(struct host1x *host,
+						unsigned int index);
 
 #endif

drivers/gpu/host1x/debug.c

@@ -43,24 +43,19 @@ void host1x_debug_output(struct output *o, const char *fmt, ...)
 	o->fn(o->ctx, o->buf, len);
 }
 
-static int show_channels(struct host1x_channel *ch, void *data, bool show_fifo)
+static int show_channel(struct host1x_channel *ch, void *data, bool show_fifo)
 {
 	struct host1x *m = dev_get_drvdata(ch->dev->parent);
 	struct output *o = data;
 
-	mutex_lock(&ch->reflock);
+	mutex_lock(&ch->cdma.lock);
 
-	if (ch->refcount) {
-		mutex_lock(&ch->cdma.lock);
+	if (show_fifo)
+		host1x_hw_show_channel_fifo(m, ch, o);
 
-		if (show_fifo)
-			host1x_hw_show_channel_fifo(m, ch, o);
+	host1x_hw_show_channel_cdma(m, ch, o);
 
-		host1x_hw_show_channel_cdma(m, ch, o);
-		mutex_unlock(&ch->cdma.lock);
-	}
-
-	mutex_unlock(&ch->reflock);
+	mutex_unlock(&ch->cdma.lock);
 
 	return 0;
 }
@@ -94,28 +89,22 @@ static void show_syncpts(struct host1x *m, struct output *o)
 	host1x_debug_output(o, "\n");
 }
 
-static void show_all(struct host1x *m, struct output *o)
+static void show_all(struct host1x *m, struct output *o, bool show_fifo)
 {
-	struct host1x_channel *ch;
+	int i;
 
 	host1x_hw_show_mlocks(m, o);
 	show_syncpts(m, o);
 	host1x_debug_output(o, "---- channels ----\n");
 
-	host1x_for_each_channel(m, ch)
-		show_channels(ch, o, true);
-}
-
-static void show_all_no_fifo(struct host1x *host1x, struct output *o)
-{
-	struct host1x_channel *ch;
-
-	host1x_hw_show_mlocks(host1x, o);
-	show_syncpts(host1x, o);
-	host1x_debug_output(o, "---- channels ----\n");
+	for (i = 0; i < m->info->nb_channels; ++i) {
+		struct host1x_channel *ch = host1x_channel_get_index(m, i);
 
-	host1x_for_each_channel(host1x, ch)
-		show_channels(ch, o, false);
+		if (ch) {
+			show_channel(ch, o, show_fifo);
+			host1x_channel_put(ch);
+		}
+	}
 }
 
 static int host1x_debug_show_all(struct seq_file *s, void *unused)
@@ -125,7 +114,7 @@ static int host1x_debug_show_all(struct seq_file *s, void *unused)
 		.ctx = s
 	};
 
-	show_all(s->private, &o);
+	show_all(s->private, &o, true);
 
 	return 0;
 }
@@ -137,7 +126,7 @@ static int host1x_debug_show(struct seq_file *s, void *unused)
 		.ctx = s
 	};
 
-	show_all_no_fifo(s->private, &o);
+	show_all(s->private, &o, false);
 
 	return 0;
 }
@@ -216,7 +205,7 @@ void host1x_debug_dump(struct host1x *host1x)
 		.fn = write_to_printk
 	};
 
-	show_all(host1x, &o);
+	show_all(host1x, &o, true);
 }
 
 void host1x_debug_dump_syncpts(struct host1x *host1x)