Re: [PATCH 10/10] gpu: host1x: Optionally block when acquiring channel

[Dmitry Osipenko]

On 05.11.2017 14:01, Mikko Perttunen wrote:
> Add an option to host1x_channel_request to interruptibly wait for a
> free channel. This allows IOCTLs that acquire a channel to block
> the userspace.
> 

Wouldn't it be more optimal to request channel and block after job's pining,
when all patching and checks are completed? Note that right now we have locking
around submission in DRM, which I suppose should go away by making locking fine
grained.

Or maybe it would be more optimal to just iterate over channels, like I
suggested before [0]?

[0]
https://github.com/cyndis/linux/commit/9e6d87f40afb01fbe13ba65c73cb617bdfcd80b2#commitcomment-25012960

> Signed-off-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/tegra/drm.c  |  9 +++++----
>  drivers/gpu/drm/tegra/gr2d.c |  6 +++---
>  drivers/gpu/drm/tegra/gr3d.c |  6 +++---
>  drivers/gpu/host1x/channel.c | 40 ++++++++++++++++++++++++++++++----------
>  drivers/gpu/host1x/channel.h |  1 +
>  include/linux/host1x.h       |  2 +-
>  6 files changed, 43 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> index 658bc8814f38..19f77c1a76c0 100644
> --- a/drivers/gpu/drm/tegra/drm.c
> +++ b/drivers/gpu/drm/tegra/drm.c
> @@ -389,7 +389,8 @@ static int host1x_waitchk_copy_from_user(struct host1x_waitchk *dest,
>   * Request a free hardware host1x channel for this user context, or if the
>   * context already has one, bump its refcount.
>   *
> - * Returns 0 on success, or -EBUSY if there were no free hardware channels.
> + * Returns 0 on success, -EINTR if wait for a free channel was interrupted,
> + * or other error.
>   */
>  int tegra_drm_context_get_channel(struct tegra_drm_context *context)
>  {
> @@ -398,10 +399,10 @@ int tegra_drm_context_get_channel(struct tegra_drm_context *context)
>  	mutex_lock(&context->lock);
>  
>  	if (context->pending_jobs == 0) {
> -		context->channel = host1x_channel_request(client->dev);
> -		if (!context->channel) {
> +		context->channel = host1x_channel_request(client->dev, true);
> +		if (IS_ERR(context->channel)) {
>  			mutex_unlock(&context->lock);
> -			return -EBUSY;
> +			return PTR_ERR(context->channel);
>  		}
>  	}
>  
> diff --git a/drivers/gpu/drm/tegra/gr2d.c b/drivers/gpu/drm/tegra/gr2d.c
> index 3db3bcac48b9..c1853402f69b 100644
> --- a/drivers/gpu/drm/tegra/gr2d.c
> +++ b/drivers/gpu/drm/tegra/gr2d.c
> @@ -32,9 +32,9 @@ static int gr2d_init(struct host1x_client *client)
>  	unsigned long flags = HOST1X_SYNCPT_HAS_BASE;
>  	struct gr2d *gr2d = to_gr2d(drm);
>  
> -	gr2d->channel = host1x_channel_request(client->dev);
> -	if (!gr2d->channel)
> -		return -ENOMEM;
> +	gr2d->channel = host1x_channel_request(client->dev, false);
> +	if (IS_ERR(gr2d->channel))
> +		return PTR_ERR(gr2d->channel);
>  
>  	client->syncpts[0] = host1x_syncpt_request(client->dev, flags);
>  	if (!client->syncpts[0]) {
> diff --git a/drivers/gpu/drm/tegra/gr3d.c b/drivers/gpu/drm/tegra/gr3d.c
> index 279438342c8c..793a91d577cb 100644
> --- a/drivers/gpu/drm/tegra/gr3d.c
> +++ b/drivers/gpu/drm/tegra/gr3d.c
> @@ -42,9 +42,9 @@ static int gr3d_init(struct host1x_client *client)
>  	unsigned long flags = HOST1X_SYNCPT_HAS_BASE;
>  	struct gr3d *gr3d = to_gr3d(drm);
>  
> -	gr3d->channel = host1x_channel_request(client->dev);
> -	if (!gr3d->channel)
> -		return -ENOMEM;
> +	gr3d->channel = host1x_channel_request(client->dev, false);
> +	if (IS_ERR(gr3d->channel))
> +		return PTR_ERR(gr3d->channel);
>  
>  	client->syncpts[0] = host1x_syncpt_request(client->dev, flags);
>  	if (!client->syncpts[0]) {
> diff --git a/drivers/gpu/host1x/channel.c b/drivers/gpu/host1x/channel.c
> index 9d8cad12f9d8..eebcd51261df 100644
> --- a/drivers/gpu/host1x/channel.c
> +++ b/drivers/gpu/host1x/channel.c
> @@ -43,6 +43,7 @@ int host1x_channel_list_init(struct host1x_channel_list *chlist,
>  	bitmap_zero(chlist->allocated_channels, num_channels);
>  
>  	mutex_init(&chlist->lock);
> +	sema_init(&chlist->sema, num_channels);
>  
>  	return 0;
>  }
> @@ -99,6 +100,8 @@ static void release_channel(struct kref *kref)
>  	host1x_cdma_deinit(&channel->cdma);
>  
>  	clear_bit(channel->id, chlist->allocated_channels);
> +
> +	up(&chlist->sema);
>  }
>  
>  void host1x_channel_put(struct host1x_channel *channel)
> @@ -107,19 +110,30 @@ void host1x_channel_put(struct host1x_channel *channel)
>  }
>  EXPORT_SYMBOL(host1x_channel_put);
>  
> -static struct host1x_channel *acquire_unused_channel(struct host1x *host)
> +static struct host1x_channel *acquire_unused_channel(struct host1x *host,
> +						     bool wait)
>  {
>  	struct host1x_channel_list *chlist = &host->channel_list;
>  	unsigned int max_channels = host->info->nb_channels;
>  	unsigned int index;
> +	int err;
> +
> +	if (wait) {
> +		err = down_interruptible(&chlist->sema);
> +		if (err)
> +			return ERR_PTR(err);
> +	} else {
> +		if (down_trylock(&chlist->sema))
> +			return ERR_PTR(-EBUSY);
> +	}
>  
>  	mutex_lock(&chlist->lock);
>  
>  	index = find_first_zero_bit(chlist->allocated_channels, max_channels);
> -	if (index >= max_channels) {
> +	if (WARN(index >= max_channels, "failed to find free channel")) {
>  		mutex_unlock(&chlist->lock);
>  		dev_err(host->dev, "failed to find free channel\n");
> -		return NULL;
> +		return ERR_PTR(-EBUSY);
>  	}
>  
>  	chlist->channels[index].id = index;
> @@ -134,20 +148,26 @@ static struct host1x_channel *acquire_unused_channel(struct host1x *host)
>  /**
>   * host1x_channel_request() - Allocate a channel
>   * @device: Host1x unit this channel will be used to send commands to
> + * @wait: Whether to wait for a free channels if all are reserved
> + *
> + * Allocates a new host1x channel for @device. If all channels are in use,
> + * and @wait is true, does an interruptible wait until one is available.
>   *
> - * Allocates a new host1x channel for @device. May return NULL if CDMA
> - * initialization fails.
> + * If a channel was acquired, returns a pointer to it. Otherwise returns
> + * an error pointer with -EINTR if the wait was interrupted, -EBUSY
> + * if a channel could not be acquired or another error code if channel
> + * initialization failed.
>   */
> -struct host1x_channel *host1x_channel_request(struct device *dev)
> +struct host1x_channel *host1x_channel_request(struct device *dev, bool wait)
>  {
>  	struct host1x *host = dev_get_drvdata(dev->parent);
>  	struct host1x_channel_list *chlist = &host->channel_list;
>  	struct host1x_channel *channel;
>  	int err;
>  
> -	channel = acquire_unused_channel(host);
> -	if (!channel)
> -		return NULL;
> +	channel = acquire_unused_channel(host, wait);
> +	if (IS_ERR(channel))
> +		return channel;
>  
>  	kref_init(&channel->refcount);
>  	mutex_init(&channel->submitlock);
> @@ -168,6 +188,6 @@ struct host1x_channel *host1x_channel_request(struct device *dev)
>  
>  	dev_err(dev, "failed to initialize channel\n");
>  
> -	return NULL;
> +	return ERR_PTR(err);
>  }
>  EXPORT_SYMBOL(host1x_channel_request);
> diff --git a/drivers/gpu/host1x/channel.h b/drivers/gpu/host1x/channel.h
> index e68a8ae9a670..1f5cf8029b62 100644
> --- a/drivers/gpu/host1x/channel.h
> +++ b/drivers/gpu/host1x/channel.h
> @@ -31,6 +31,7 @@ struct host1x_channel_list {
>  	struct host1x_channel *channels;
>  
>  	struct mutex lock;
> +	struct semaphore sema;
>  	unsigned long *allocated_channels;
>  };
>  
> diff --git a/include/linux/host1x.h b/include/linux/host1x.h
> index f931d28a68ff..2a34905d4408 100644
> --- a/include/linux/host1x.h
> +++ b/include/linux/host1x.h
> @@ -171,7 +171,7 @@ u32 host1x_syncpt_base_id(struct host1x_syncpt_base *base);
>  struct host1x_channel;
>  struct host1x_job;
>  
> -struct host1x_channel *host1x_channel_request(struct device *dev);
> +struct host1x_channel *host1x_channel_request(struct device *dev, bool wait);
>  struct host1x_channel *host1x_channel_get(struct host1x_channel *channel);
>  void host1x_channel_put(struct host1x_channel *channel);
>  int host1x_job_submit(struct host1x_job *job);
>