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Message-ID: <38340901-7016-3444-5ace-64159b32f1c7@kapsi.fi>
Date: Tue, 7 Nov 2017 15:11:07 +0200
From: Mikko Perttunen <cyndis@...si.fi>
To: Dmitry Osipenko <digetx@...il.com>,
Mikko Perttunen <mperttunen@...dia.com>,
thierry.reding@...il.com, jonathanh@...dia.com
Cc: dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] gpu: host1x: Optionally block when acquiring
channel
On 05.11.2017 19:14, Dmitry Osipenko wrote:
> 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.
That would be possible, but I don't think it should matter much since
contention here should not be the common case.
>
> Or maybe it would be more optimal to just iterate over channels, like I
> suggested before [0]?
Somehow I hadn't noticed this before, but this would break the invariant
of having one client/class per channel.
In general since we haven't seen any issues downstream with the model
implemented here, I'd like to try to go with this and if we have
problems with channel allocation then we could revisit.
Mikko
>
> [0]
> https://github.com/cyndis/linux/commit/9e6d87f40afb01fbe13ba65c73cb617bdfcd80b2#commitcomment-25012960
>
>> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
>> ---
>> 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);
>>
>
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