On Wed, Sep 04, 2024 at 10:35:18AM +0200, Jacopo Mondi wrote:
> Hi Laurent
>
> On Wed, Sep 04, 2024 at 10:53:02AM GMT, Laurent Pinchart wrote:
> > On Wed, Sep 04, 2024 at 09:21:45AM +0200, Jacopo Mondi wrote:
> > > Hi Laurent
> > >
> > > On Tue, Sep 03, 2024 at 03:19:36PM GMT, Laurent Pinchart wrote:
> > > > Hi Jacopo,
> > > >
> > > > Thank you for the patch.
> > > >
> > > > I just noticed the subject line writes "pisp-be" while all other patches
> > > > in the series use "pisp_be".
> > > >
> > > > On Mon, Sep 02, 2024 at 01:24:05PM +0200, Jacopo Mondi wrote:
> > > > > Currently the 'pispbe_schedule()' function does two things:
> > > > >
> > > > > 1) Tries to assemble a job by inspecting all the video node queues
> > > > > to make sure all the required buffers are available
> > > > > 2) Submit the job to the hardware
> > > > >
> > > > > The pispbe_schedule() function is called at:
> > > > >
> > > > > - video device start_streaming() time
> > > > > - video device qbuf() time
> > > > > - irq handler
> > > > >
> > > > > As assembling a job requires inspecting all queues, it is a rather
> > > > > time consuming operation which is better not run in IRQ context.
> > > > >
> > > > > To avoid the executing the time consuming job creation in interrupt
> > > > > context split the job creation and job scheduling in two distinct
> > > > > operations. When a well-formed job is created, append it to the
> > > > > newly introduced 'pispbe->job_queue' where it will be dequeued from
> > > > > by the scheduling routine.
> > > > >
> > > > > At start_streaming() and qbuf() time immediately try to schedule a job
> > > > > if one has been created as the irq handler routing is only called when
> > > > > a job has completed, and we can't solely rely on it for scheduling new
> > > > > jobs.
> > > > >
> > > > > As now the per-node 'ready_queue' buffer list is only accessed in vb2
> > > > > ops callbacks, protected by a mutex, it is not necessary to guard it
> > > > > with a dedicated spinlock so drop it.
> > > > >
> > > > > Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx>
> > > > > ---
> > > > > .../platform/raspberrypi/pisp_be/pisp_be.c | 134 ++++++++++--------
> > > > > 1 file changed, 73 insertions(+), 61 deletions(-)
> > > > >
> > > > > diff --git a/drivers/media/platform/raspberrypi/pisp_be/pisp_be.c b/drivers/media/platform/raspberrypi/pisp_be/pisp_be.c
> > > > > index 41fd68b7757b..d614f53f0f68 100644
> > > > > --- a/drivers/media/platform/raspberrypi/pisp_be/pisp_be.c
> > > > > +++ b/drivers/media/platform/raspberrypi/pisp_be/pisp_be.c
> > > > > @@ -161,8 +161,6 @@ struct pispbe_node {
> > > > > struct mutex node_lock;
> > > > > /* vb2_queue lock */
> > > > > struct mutex queue_lock;
> > > > > - /* Protect pispbe_node->ready_queue and pispbe_buffer->ready_list */
> > > > > - spinlock_t ready_lock;
> > > > > struct list_head ready_queue;
> > > > > struct vb2_queue queue;
> > > > > struct v4l2_format format;
> > > > > @@ -190,6 +188,8 @@ struct pispbe_hw_enables {
> > > > >
> > > > > /* Records a job configuration and memory addresses. */
> > > > > struct pispbe_job_descriptor {
> > > > > + struct list_head queue;
> > > > > + struct pispbe_buffer *buffers[PISPBE_NUM_NODES];
> > > > > dma_addr_t hw_dma_addrs[N_HW_ADDRESSES];
> > > > > struct pisp_be_tiles_config *config;
> > > > > struct pispbe_hw_enables hw_enables;
> > > > > @@ -215,8 +215,10 @@ struct pispbe_dev {
> > > > > unsigned int sequence;
> > > > > u32 streaming_map;
> > > > > struct pispbe_job queued_job, running_job;
> > > > > - spinlock_t hw_lock; /* protects "hw_busy" flag and streaming_map */
> > > > > + /* protects "hw_busy" flag, streaming_map and job_queue */
> > > > > + spinlock_t hw_lock;
> > > > > bool hw_busy; /* non-zero if a job is queued or is being started */
> > > > > + struct list_head job_queue;
> > > > > int irq;
> > > > > u32 hw_version;
> > > > > u8 done, started;
> > > > > @@ -440,41 +442,47 @@ static void pispbe_xlate_addrs(struct pispbe_dev *pispbe,
> > > > > * For Output0, Output1, Tdn and Stitch, a buffer only needs to be
> > > > > * available if the blocks are enabled in the config.
> > > > > *
> > > > > - * Needs to be called with hw_lock held.
> > > > > + * If all the buffers required to form a job are available, append the
> > > > > + * job descriptor to the job queue to be later queued to the HW.
> > > > > *
> > > > > * Returns 0 if a job has been successfully prepared, < 0 otherwise.
> > > > > */
> > > > > -static int pispbe_prepare_job(struct pispbe_dev *pispbe,
> > > > > - struct pispbe_job_descriptor *job)
> > > > > +static int pispbe_prepare_job(struct pispbe_dev *pispbe)
> > > > > {
> > > > > struct pispbe_buffer *buf[PISPBE_NUM_NODES] = {};
> > > > > + struct pispbe_job_descriptor *job;
> > > > > + unsigned int streaming_map;
> > > > > unsigned int config_index;
> > > > > struct pispbe_node *node;
> > > > > - unsigned long flags;
> > > > >
> > > > > - lockdep_assert_held(&pispbe->hw_lock);
> > > > > + scoped_guard(spinlock, &pispbe->hw_lock) {
> > > >
> > > > I think I've mis-communicated the locking requirements. This spinlock is
> > > > taken in both non-IRQ contexts (here) and in mixed IRQ and non-IRQ
> > > > contexts (pispbe_schedule(), called from both IRQ context in
> > > > pispbe_isr() and non-IRQ context in pispbe_node_buffer_queue() and
> > > > pispbe_node_start_streaming()).
> > > >
> > > > This means that the non-IRQ contexts should use spinlock_irq(), and the
> > > > mixed contexts should use spinlock_irqsave().
> > > >
> > >
> > > Yeah sorry, I admit I hadn't put much attention to this
> > >
> > > > > + static const u32 mask = BIT(CONFIG_NODE) | BIT(MAIN_INPUT_NODE);
> > > > >
> > > > > - memset(job, 0, sizeof(struct pispbe_job_descriptor));
> > > > > + if ((pispbe->streaming_map & mask) != mask)
> > > > > + return -ENODEV;
> > > > >
> > > > > - if (((BIT(CONFIG_NODE) | BIT(MAIN_INPUT_NODE)) &
> > > > > - pispbe->streaming_map) !=
> > > > > - (BIT(CONFIG_NODE) | BIT(MAIN_INPUT_NODE)))
> > > > > - return -ENODEV;
> > > > > + /*
> > > > > + * Take a copy of streaming_map: nodes activated after this
> > > > > + * point are ignored when preparing this job.
> > > > > + */
> > > > > + streaming_map = pispbe->streaming_map;
> > > > > + }
> > > > > +
> > > > > + job = kzalloc(sizeof(*job), GFP_KERNEL);
> > > > > + if (!job)
> > > > > + return -ENOMEM;
> > > > >
> > > > > node = &pispbe->node[CONFIG_NODE];
> > > > > - spin_lock_irqsave(&node->ready_lock, flags);
> > > > > buf[CONFIG_NODE] = list_first_entry_or_null(&node->ready_queue,
> > > > > struct pispbe_buffer,
> > > > > ready_list);
> > > > > - if (buf[CONFIG_NODE]) {
> > > > > - list_del(&buf[CONFIG_NODE]->ready_list);
> > > > > - pispbe->queued_job.buf[CONFIG_NODE] = buf[CONFIG_NODE];
> > > > > + if (!buf[CONFIG_NODE]) {
> > > > > + kfree(job);
> > > > > + return -ENODEV;
> > > > > }
> > > > > - spin_unlock_irqrestore(&node->ready_lock, flags);
> > > > >
> > > > > - /* Exit early if no config buffer has been queued. */
> > > > > - if (!buf[CONFIG_NODE])
> > > > > - return -ENODEV;
> > > > > + list_del(&buf[CONFIG_NODE]->ready_list);
> > > > > + job->buffers[CONFIG_NODE] = buf[CONFIG_NODE];
> > > > >
> > > > > config_index = buf[CONFIG_NODE]->vb.vb2_buf.index;
> > > > > job->config = &pispbe->config[config_index];
> > > > > @@ -495,7 +503,7 @@ static int pispbe_prepare_job(struct pispbe_dev *pispbe,
> > > > > continue;
> > > > >
> > > > > buf[i] = NULL;
> > > > > - if (!(pispbe->streaming_map & BIT(i)))
> > > > > + if (!(streaming_map & BIT(i)))
> > > > > continue;
> > > > >
> > > > > if ((!(rgb_en & PISP_BE_RGB_ENABLE_OUTPUT0) &&
> > > > > @@ -522,25 +530,25 @@ static int pispbe_prepare_job(struct pispbe_dev *pispbe,
> > > > > node = &pispbe->node[i];
> > > > >
> > > > > /* Pull a buffer from each V4L2 queue to form the queued job */
> > > > > - spin_lock_irqsave(&node->ready_lock, flags);
> > > > > buf[i] = list_first_entry_or_null(&node->ready_queue,
> > > > > struct pispbe_buffer,
> > > > > ready_list);
> > > > > if (buf[i]) {
> > > > > list_del(&buf[i]->ready_list);
> > > > > - pispbe->queued_job.buf[i] = buf[i];
> > > > > + job->buffers[i] = buf[i];
> > > > > }
> > > > > - spin_unlock_irqrestore(&node->ready_lock, flags);
> > > > >
> > > > > if (!buf[i] && !ignore_buffers)
> > > > > goto err_return_buffers;
> > > > > }
> > > > >
> > > > > - pispbe->queued_job.valid = true;
> > > > > -
> > > > > /* Convert buffers to DMA addresses for the hardware */
> > > > > pispbe_xlate_addrs(pispbe, job, buf);
> > > > >
> > > > > + spin_lock(&pispbe->hw_lock);
> > > > > + list_add_tail(&job->queue, &pispbe->job_queue);
> > > > > + spin_unlock(&pispbe->hw_lock);
> > > > > +
> > > > > return 0;
> > > > >
> > > > > err_return_buffers:
> > > > > @@ -551,33 +559,39 @@ static int pispbe_prepare_job(struct pispbe_dev *pispbe,
> > > > > continue;
> > > > >
> > > > > /* Return the buffer to the ready_list queue */
> > > > > - spin_lock_irqsave(&n->ready_lock, flags);
> > > > > list_add(&buf[i]->ready_list, &n->ready_queue);
> > > > > - spin_unlock_irqrestore(&n->ready_lock, flags);
> > > > > }
> > > > >
> > > > > - memset(&pispbe->queued_job, 0, sizeof(pispbe->queued_job));
> > > > > + kfree(job);
> > > > >
> > > > > return -ENODEV;
> > > > > }
> > > > >
> > > > > static void pispbe_schedule(struct pispbe_dev *pispbe, bool clear_hw_busy)
> > > > > {
> > > > > - struct pispbe_job_descriptor job;
> > > > > - unsigned long flags;
> > > > > - int ret;
> > > > > + struct pispbe_job_descriptor *job;
> > > > >
> > > > > - spin_lock_irqsave(&pispbe->hw_lock, flags);
> > > > > + scoped_guard(spinlock, &pispbe->hw_lock) {
> > > > > + if (clear_hw_busy)
> > > > > + pispbe->hw_busy = false;
> > > > > +
> > > > > + if (pispbe->hw_busy)
> > > > > + return;
> > > > >
> > > > > - if (clear_hw_busy)
> > > > > - pispbe->hw_busy = false;
> > > > > + job = list_first_entry_or_null(&pispbe->job_queue,
> > > > > + struct pispbe_job_descriptor,
> > > > > + queue);
> > > > > + if (!job)
> > > > > + return;
> > > > >
> > > > > - if (pispbe->hw_busy)
> > > > > - goto unlock_and_return;
> > > > > + list_del(&job->queue);
> > > > >
> > > > > - ret = pispbe_prepare_job(pispbe, &job);
> > > > > - if (ret)
> > > > > - goto unlock_and_return;
> > > > > + for (unsigned int i = 0; i < PISPBE_NUM_NODES; i++)
> > > > > + pispbe->queued_job.buf[i] = job->buffers[i];
> > > > > + pispbe->queued_job.valid = true;
> > > > > +
> > > > > + pispbe->hw_busy = true;
> > > > > + }
> > > > >
> > > > > /*
> > > > > * We can kick the job off without the hw_lock, as this can
> > > > > @@ -585,16 +599,8 @@ static void pispbe_schedule(struct pispbe_dev *pispbe, bool clear_hw_busy)
> > > > > * only when the following job has been queued and an interrupt
> > > > > * is rised.
> > > > > */
> > > > > - pispbe->hw_busy = true;
> > > > > - spin_unlock_irqrestore(&pispbe->hw_lock, flags);
> > > > > -
> > > > > - pispbe_queue_job(pispbe, &job);
> > > > > -
> > > > > - return;
> > > > > -
> > > > > -unlock_and_return:
> > > > > - /* No job has been queued, just release the lock and return. */
> > > > > - spin_unlock_irqrestore(&pispbe->hw_lock, flags);
> > > > > + pispbe_queue_job(pispbe, job);
> > > > > + kfree(job);
> > > > > }
> > > > >
> > > > > static void pispbe_isr_jobdone(struct pispbe_dev *pispbe,
> > > > > @@ -846,18 +852,16 @@ static void pispbe_node_buffer_queue(struct vb2_buffer *buf)
> > > > > container_of(vbuf, struct pispbe_buffer, vb);
> > > > > struct pispbe_node *node = vb2_get_drv_priv(buf->vb2_queue);
> > > > > struct pispbe_dev *pispbe = node->pispbe;
> > > > > - unsigned long flags;
> > > > >
> > > > > dev_dbg(pispbe->dev, "%s: for node %s\n", __func__, NODE_NAME(node));
> > > > > - spin_lock_irqsave(&node->ready_lock, flags);
> > > > > list_add_tail(&buffer->ready_list, &node->ready_queue);
> > > > > - spin_unlock_irqrestore(&node->ready_lock, flags);
> > > > >
> > > > > /*
> > > > > * Every time we add a buffer, check if there's now some work for the hw
> > > > > * to do.
> > > > > */
> > > > > - pispbe_schedule(pispbe, false);
> > > > > + if (!pispbe_prepare_job(pispbe))
> > > > > + pispbe_schedule(pispbe, false);
> > > > > }
> > > > >
> > > > > static int pispbe_node_start_streaming(struct vb2_queue *q, unsigned int count)
> > > > > @@ -883,7 +887,8 @@ static int pispbe_node_start_streaming(struct vb2_queue *q, unsigned int count)
> > > > > node->pispbe->streaming_map);
> > > > >
> > > > > /* Maybe we're ready to run. */
> > > > > - pispbe_schedule(pispbe, false);
> > > > > + if (!pispbe_prepare_job(pispbe))
> > > > > + pispbe_schedule(pispbe, false);
> > > > >
> > > > > return 0;
> > > > >
> > > > > @@ -917,9 +922,6 @@ static void pispbe_node_stop_streaming(struct vb2_queue *q)
> > > > > dev_dbg(pispbe->dev, "%s: for node %s\n", __func__, NODE_NAME(node));
> > > > > spin_lock_irqsave(&pispbe->hw_lock, flags);
> > > >
> > > > Is the lock needed here ? And in the err_return_buffers error path in
> > > > pispbe_node_start_streaming() ? Both seem to touch the ready_queue only,
> > > > which isn't protected by the hw_lock.
> > >
> > > No the lock is not needed, and as this is not irq context I should
> > > switch both stop_streaming() and start_streaming() to use
> > > spink_lock_irq()
> > >
> > > > > do {
> > > > > - unsigned long flags1;
> > > > > -
> > > > > - spin_lock_irqsave(&node->ready_lock, flags1);
> > > > > buf = list_first_entry_or_null(&node->ready_queue,
> > > > > struct pispbe_buffer,
> > > > > ready_list);
> > > > > @@ -927,7 +929,6 @@ static void pispbe_node_stop_streaming(struct vb2_queue *q)
> > > > > list_del(&buf->ready_list);
> > > > > vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
> > > > > }
> > > > > - spin_unlock_irqrestore(&node->ready_lock, flags1);
> > > > > } while (buf);
> > > > > spin_unlock_irqrestore(&pispbe->hw_lock, flags);
> > > > >
> > > > > @@ -935,6 +936,16 @@ static void pispbe_node_stop_streaming(struct vb2_queue *q)
> > > > >
> > > > > spin_lock_irqsave(&pispbe->hw_lock, flags);
> > > > > pispbe->streaming_map &= ~BIT(node->id);
> > > > > +
> > > > > + /* Release all jobs once all nodes have stopped streaming. */
> > > > > + if (pispbe->streaming_map == 0) {
> > > > > + struct pispbe_job_descriptor *job, *temp;
> > > > > +
> > > > > + list_for_each_entry_safe(job, temp, &pispbe->job_queue, queue) {
> > > > > + list_del(&job->queue);
> > > > > + kfree(job);
> > > > > + }
> > > >
> > > > I think this can be done outside of the lock.
> > > >
> > >
> > > Does it ? The job queue is accessed by the irq handler. As we
> > > stop the interface -after- having cleared the job queue here, I would
> > > keep this sequence inside the lock to be honest.
> >
> > Ah yes you right. I'm not sure what I missed.
> >
> > What you can do here, though, is to splice the job_queue to a local list
> > with the lock, and then iterate over the local list and free the jobs
> > without the lock.
>
> Do you expect this to be such a critical path that this is reequired ?
> True, the lock is contended with the irq handler, but I don't expect
> the job queue to be that long. Do you ?
No, but kfree() is not necessarily a very cheap operation. I think it's
worth splicing the list as it's easy.
> > > > > + }
> > > > > spin_unlock_irqrestore(&pispbe->hw_lock, flags);
> > > > >
> > > > > pm_runtime_mark_last_busy(pispbe->dev);
> > > > > @@ -1393,7 +1404,6 @@ static int pispbe_init_node(struct pispbe_dev *pispbe, unsigned int id)
> > > > > mutex_init(&node->node_lock);
> > > > > mutex_init(&node->queue_lock);
> > > > > INIT_LIST_HEAD(&node->ready_queue);
> > > > > - spin_lock_init(&node->ready_lock);
> > > > >
> > > > > node->format.type = node->buf_type;
> > > > > pispbe_node_def_fmt(node);
> > > > > @@ -1677,6 +1687,8 @@ static int pispbe_probe(struct platform_device *pdev)
> > > > > if (!pispbe)
> > > > > return -ENOMEM;
> > > > >
> > > > > + INIT_LIST_HEAD(&pispbe->job_queue);
> > > > > +
> > > > > dev_set_drvdata(&pdev->dev, pispbe);
> > > > > pispbe->dev = &pdev->dev;
> > > > > platform_set_drvdata(pdev, pispbe);
--
Regards,
Laurent Pinchart
