Commit 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") removed a redundant call to v4l2_m2m_try_run but instead introduced a bug. Consider the following case:

1) Context A schedules, queues and runs job A. 2) While the m2m device is running, context B schedules and queues job B. Job B cannot run, because it has to wait for job A. 3) Job A completes, calls v4l2_m2m_job_finish, and tries to queue a job for context A, but since the context is empty it won't do anything.

In this scenario, queued job B will never run. Fix this by calling v4l2_m2m_try_run from v4l2_m2m_try_schedule.

While here, add more documentation to these functions.

Fixes: 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") Signed-off-by: Ezequiel Garcia ezequiel@collabora.com --- drivers/media/v4l2-core/v4l2-mem2mem.c | 32 +++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c index 5f9cd5b74cda..dfd796621b06 100644 --- a/drivers/media/v4l2-core/v4l2-mem2mem.c +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c @@ -209,15 +209,23 @@ static void v4l2_m2m_try_run(struct v4l2_m2m_dev *m2m_dev) m2m_dev->curr_ctx->job_flags |= TRANS_RUNNING; spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);

+ dprintk("Running job on m2m_ctx: %p\n", m2m_dev->curr_ctx); m2m_dev->m2m_ops->device_run(m2m_dev->curr_ctx->priv); }

-void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +/* + * __v4l2_m2m_try_queue() - queue a job + * @m2m_dev: m2m device + * @m2m_ctx: m2m context + * + * Check if this context is ready to queue a job. + * + * This function can run in interrupt context. + */ +static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev, struct v4l2_m2m_ctx *m2m_ctx) { - struct v4l2_m2m_dev *m2m_dev; unsigned long flags_job, flags_out, flags_cap;

- m2m_dev = m2m_ctx->m2m_dev; dprintk("Trying to schedule a job for m2m_ctx: %p\n", m2m_ctx);

if (!m2m_ctx->out_q_ctx.q.streaming @@ -275,7 +283,25 @@ void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) m2m_ctx->job_flags |= TRANS_QUEUED;

spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); +} + +/** + * v4l2_m2m_try_schedule() - schedule and possibly run a job for any context + * @m2m_ctx: m2m context + * + * Check if this context is ready to queue a job. If suitable, + * run the next queued job on the mem2mem device. + * + * This function shouldn't run in interrupt context. + * + * Note that v4l2_m2m_try_schedule() can schedule one job for this context, + * and then run another job for another context. + */ +void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +{ + struct v4l2_m2m_dev *m2m_dev = m2m_ctx->m2m_dev;

+ __v4l2_m2m_try_queue(m2m_dev, m2m_ctx); v4l2_m2m_try_run(m2m_dev); } EXPORT_SYMBOL_GPL(v4l2_m2m_try_schedule);

From: Sakari Ailus sakari.ailus@linux.intel.com

The __v4l2_m2m_try_schedule function acquires and releases multiple spinlocks. Simplify unlocking the job lock by adding labels to unlock the lock and exit the function.

Signed-off-by: Sakari Ailus sakari.ailus@linux.intel.com Signed-off-by: Ezequiel Garcia ezequiel@collabora.com --- drivers/media/v4l2-core/v4l2-mem2mem.c | 29 ++++++++++++-------------- 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c index 69a91c0030be..a25b45d8abeb 100644 --- a/drivers/media/v4l2-core/v4l2-mem2mem.c +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c @@ -238,51 +238,48 @@ static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev, struct v4l2_m2m_c

/* If the context is aborted then don't schedule it */ if (m2m_ctx->job_flags & TRANS_ABORT) { - spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); dprintk("Aborted context\n"); - return; + goto job_unlock; }

if (m2m_ctx->job_flags & TRANS_QUEUED) { - spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); dprintk("On job queue already\n"); - return; + goto job_unlock; }

spin_lock_irqsave(&m2m_ctx->out_q_ctx.rdy_spinlock, flags_out); if (list_empty(&m2m_ctx->out_q_ctx.rdy_queue) && !m2m_ctx->out_q_ctx.buffered) { - spin_unlock_irqrestore(&m2m_ctx->out_q_ctx.rdy_spinlock, - flags_out); - spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); dprintk("No input buffers available\n"); - return; + goto out_unlock; } spin_lock_irqsave(&m2m_ctx->cap_q_ctx.rdy_spinlock, flags_cap); if (list_empty(&m2m_ctx->cap_q_ctx.rdy_queue) && !m2m_ctx->cap_q_ctx.buffered) { - spin_unlock_irqrestore(&m2m_ctx->cap_q_ctx.rdy_spinlock, - flags_cap); - spin_unlock_irqrestore(&m2m_ctx->out_q_ctx.rdy_spinlock, - flags_out); - spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); dprintk("No output buffers available\n"); - return; + goto cap_unlock; } spin_unlock_irqrestore(&m2m_ctx->cap_q_ctx.rdy_spinlock, flags_cap); spin_unlock_irqrestore(&m2m_ctx->out_q_ctx.rdy_spinlock, flags_out);

if (m2m_dev->m2m_ops->job_ready && (!m2m_dev->m2m_ops->job_ready(m2m_ctx->priv))) { - spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); dprintk("Driver not ready\n"); - return; + goto job_unlock; }

list_add_tail(&m2m_ctx->queue, &m2m_dev->job_queue); m2m_ctx->job_flags |= TRANS_QUEUED;

spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); + return; + +cap_unlock: + spin_unlock_irqrestore(&m2m_ctx->cap_q_ctx.rdy_spinlock, flags_cap); +out_unlock: + spin_unlock_irqrestore(&m2m_ctx->out_q_ctx.rdy_spinlock, flags_out); +job_unlock: + spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); }

/**

Add a test for the memory-to-memory framework, to exercise the scheduling of concurrent jobs, using multiple contexts.

This test needs to be run using the vim2m virtual driver, and so needs no hardware.

Signed-off-by: Ezequiel Garcia ezequiel@collabora.com --- tools/testing/selftests/media_tests/Makefile | 4 +- .../selftests/media_tests/m2m_job_test.c | 283 ++++++++++++++++++ 2 files changed, 286 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/media_tests/m2m_job_test.c

diff --git a/tools/testing/selftests/media_tests/Makefile b/tools/testing/selftests/media_tests/Makefile index 60826d7d37d4..d2e8a6b685fb 100644 --- a/tools/testing/selftests/media_tests/Makefile +++ b/tools/testing/selftests/media_tests/Makefile @@ -1,6 +1,8 @@ # SPDX-License-Identifier: GPL-2.0 # CFLAGS += -I../ -I../../../../usr/include/ -TEST_GEN_PROGS := media_device_test media_device_open video_device_test +TEST_GEN_PROGS := media_device_test media_device_open video_device_test m2m_job_test

include ../lib.mk + +LDLIBS += -lpthread diff --git a/tools/testing/selftests/media_tests/m2m_job_test.c b/tools/testing/selftests/media_tests/m2m_job_test.c new file mode 100644 index 000000000000..673e7b5cea3a --- /dev/null +++ b/tools/testing/selftests/media_tests/m2m_job_test.c @@ -0,0 +1,283 @@ +// SPDX-License-Identifier: GPL-2.0 +// +// Copyright (c) Collabora, Ltd. + +/* + * This file adds a test for the memory-to-memory + * framework. + * + * This test opens a user specified video device and then + * queues concurrent jobs. The jobs are totally dummy, + * its purpose is only to verify that each of the queued + * jobs is run, and is run only once. + * + * The vim2m driver is needed in order to run the test. + * + * Usage: + * ./m2m-job-test -d /dev/videoX + */ + +#include <assert.h> +#include <errno.h> +#include <fcntl.h> +#include <unistd.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/ioctl.h> +#include <sys/stat.h> +#include <time.h> +#include <pthread.h> +#include <poll.h> + +#include <linux/videodev2.h> + +#define V4L2_CID_TRANS_TIME_MSEC (V4L2_CID_USER_BASE + 0x1000) +#define V4L2_CID_TRANS_NUM_BUFS (V4L2_CID_USER_BASE + 0x1001) + +#define MAX_TRANS_TIME_MSEC 500 +#define MAX_COUNT 300 +#define MAX_BUFFERS 5 +#define W 100 +#define H 100 + +#ifndef DEBUG +#define dprintf(fmt, arg...) \ + do { \ + } while (0) +#else +#define dprintf(fmt, arg...) printf(fmt, ## arg) +#endif + +static char video_device[256]; +static int thread_count; + +struct context { + int vfd; + unsigned int width; + unsigned int height; + int buffers; +}; + +static int req_src_buf(struct context *ctx, int buffers) +{ + struct v4l2_requestbuffers reqbuf; + struct v4l2_buffer buf; + int i, ret; + + memset(&reqbuf, 0, sizeof(reqbuf)); + memset(&buf, 0, sizeof(buf)); + + reqbuf.count = buffers; + reqbuf.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; + reqbuf.memory = V4L2_MEMORY_MMAP; + ret = ioctl(ctx->vfd, VIDIOC_REQBUFS, &reqbuf); + if (ret) + return ret; + + for (i = 0; i < buffers; i++) { + buf.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = i; + ret = ioctl(ctx->vfd, VIDIOC_QUERYBUF, &buf); + if (ret) + return ret; + buf.bytesused = W*H*2; + ret = ioctl(ctx->vfd, VIDIOC_QBUF, &buf); + if (ret) + return ret; + } + + return 0; +} + +static int req_dst_buf(struct context *ctx, int buffers) +{ + struct v4l2_requestbuffers reqbuf; + struct v4l2_buffer buf; + int i, ret; + + memset(&reqbuf, 0, sizeof(reqbuf)); + memset(&buf, 0, sizeof(buf)); + + reqbuf.count = buffers; + reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + reqbuf.memory = V4L2_MEMORY_MMAP; + + ret = ioctl(ctx->vfd, VIDIOC_REQBUFS, &reqbuf); + if (ret) + return ret; + + for (i = 0; i < buffers; i++) { + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = i; + ret = ioctl(ctx->vfd, VIDIOC_QUERYBUF, &buf); + if (ret) + return ret; + ret = ioctl(ctx->vfd, VIDIOC_QBUF, &buf); + if (ret) + return ret; + } + return 0; +} + +static int streamon(struct context *ctx) +{ + enum v4l2_buf_type type; + int ret; + + type = V4L2_BUF_TYPE_VIDEO_OUTPUT; + ret = ioctl(ctx->vfd, VIDIOC_STREAMON, &type); + if (ret) + return ret; + + type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + ret = ioctl(ctx->vfd, VIDIOC_STREAMON, &type); + if (ret) + return ret; + + return ret; +} + +static int dqbuf(struct context *ctx) +{ + struct v4l2_buffer buf; + struct pollfd fds[] = { + { .fd = ctx->vfd, .events = POLLIN }, + }; + int i, ret, tout; + + tout = (MAX_TRANS_TIME_MSEC + 10) * thread_count * 2; + for (i = 0; i < ctx->buffers; i++) { + ret = poll(fds, 1, tout); + if (ret == -1) { + if (errno == EINTR) + continue; + return -1; + } + + if (ret == 0) { + dprintf("%s: timeout on %p\n", __func__, ctx); + return -1; + } + + dprintf("%s: event on %p\n", __func__, ctx); + + memset(&buf, 0, sizeof(buf)); + buf.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = i; + ret = ioctl(ctx->vfd, VIDIOC_DQBUF, &buf); + if (ret) { + dprintf("%s: VIDIOC_DQBUF failed %p\n", __func__, ctx); + return ret; + } + + memset(&buf, 0, sizeof(buf)); + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = i; + ret = ioctl(ctx->vfd, VIDIOC_DQBUF, &buf); + if (ret) { + dprintf("%s: VIDIOC_DQBUF failed %p\n", __func__, ctx); + return ret; + } + } + + return 0; +} + +static void *job(void *arg) +{ + struct context *ctx = (struct context *)arg; + + dprintf("%s: running %p\n", __func__, ctx); + + assert(streamon(ctx) == 0); + assert(dqbuf(ctx) == 0); + assert(dqbuf(ctx) != 0); + close(ctx->vfd); + + dprintf("%s: %p done\n", __func__, ctx); + return NULL; +} + +static void init(struct context *ctx) +{ + struct v4l2_ext_controls ext_ctrls; + struct v4l2_ext_control ctrls[2]; + struct v4l2_capability cap; + int ret, buffers; + + memset(ctx, 0, sizeof(*ctx)); + + ctx->vfd = open(video_device, O_RDWR | O_NONBLOCK, 0); + ctx->width = W; + ctx->height = H; + assert(ctx->vfd >= 0); + + ret = ioctl(ctx->vfd, VIDIOC_QUERYCAP, &cap); + assert(ret == 0); + assert(cap.device_caps & V4L2_CAP_VIDEO_M2M); + assert(strcmp((const char *)cap.driver, "vim2m") == 0); + + ctrls[0].id = V4L2_CID_TRANS_TIME_MSEC; + ctrls[0].value = rand() % MAX_TRANS_TIME_MSEC + 10; + ctrls[1].id = V4L2_CID_TRANS_NUM_BUFS; + ctrls[1].value = 1; + + memset(&ext_ctrls, 0, sizeof(ext_ctrls)); + ext_ctrls.count = 2; + ext_ctrls.controls = ctrls; + ret = ioctl(ctx->vfd, VIDIOC_S_EXT_CTRLS, &ext_ctrls); + assert(ret == 0); + + buffers = rand() % MAX_BUFFERS + 1; + assert(req_src_buf(ctx, buffers) == 0); + assert(req_dst_buf(ctx, buffers) == 0); + ctx->buffers = buffers; +} + +int main(int argc, char * const argv[]) +{ + int i, opt; + + if (argc < 2) { + printf("Usage: %s [-d </dev/videoX>]\n", argv[0]); + exit(-1); + } + + /* Process arguments */ + while ((opt = getopt(argc, argv, "d:")) != -1) { + switch (opt) { + case 'd': + strncpy(video_device, optarg, sizeof(video_device) - 1); + video_device[sizeof(video_device)-1] = '\0'; + break; + default: + printf("Usage: %s [-d </dev/videoX>]\n", argv[0]); + exit(-1); + } + } + + /* Generate random number of interations */ + srand((unsigned int) time(NULL)); + thread_count = rand() % MAX_COUNT + 1; + + pthread_t in_thread[thread_count]; + struct context ctx[thread_count]; + + printf("Running %d threads\n", thread_count); + + for (i = 0; i < thread_count; i++) + init(&ctx[i]); + + for (i = 0; i < thread_count; i++) + pthread_create(&in_thread[i], NULL, job, &ctx[i]); + + for (i = 0; i < thread_count; i++) + pthread_join(in_thread[i], NULL); + + return 0; +}

On 27/07/18 15:35, Hans Verkuil wrote:

On 25/07/18 19:15, Ezequiel Garcia wrote:

...

Commit 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") removed a redundant call to v4l2_m2m_try_run but instead introduced a bug. Consider the following case:

1. Context A schedules, queues and runs job A.
2. While the m2m device is running, context B schedules and queues job B. Job B cannot run, because it has to wait for job A.
3. Job A completes, calls v4l2_m2m_job_finish, and tries to queue a job for context A, but since the context is empty it won't do anything.

In this scenario, queued job B will never run. Fix this by calling v4l2_m2m_try_run from v4l2_m2m_try_schedule.

While here, add more documentation to these functions.

Fixes: 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") Signed-off-by: Ezequiel Garcia ezequiel@collabora.com

So just to be clear: this first patch fixes a regression and can be applied separately from the other patches?

...

---

drivers/media/v4l2-core/v4l2-mem2mem.c | 32 +++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c index 5f9cd5b74cda..dfd796621b06 100644 --- a/drivers/media/v4l2-core/v4l2-mem2mem.c +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c @@ -209,15 +209,23 @@ static void v4l2_m2m_try_run(struct v4l2_m2m_dev *m2m_dev) m2m_dev->curr_ctx->job_flags |= TRANS_RUNNING; spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);

• dprintk("Running job on m2m_ctx: %p\n", m2m_dev->curr_ctx);

Is this intended? It feels out of place in this patch.

...

m2m_dev->m2m_ops->device_run(m2m_dev->curr_ctx->priv); } -void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +/*

• • __v4l2_m2m_try_queue() - queue a job
• • @m2m_dev: m2m device
• • @m2m_ctx: m2m context
• • Check if this context is ready to queue a job.
• • This function can run in interrupt context.
• */

+static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev, struct v4l2_m2m_ctx *m2m_ctx) {

• struct v4l2_m2m_dev *m2m_dev; unsigned long flags_job, flags_out, flags_cap;

• m2m_dev = m2m_ctx->m2m_dev; dprintk("Trying to schedule a job for m2m_ctx: %p\n", m2m_ctx);

if (!m2m_ctx->out_q_ctx.q.streaming @@ -275,7 +283,25 @@ void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) m2m_ctx->job_flags |= TRANS_QUEUED; spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); +}

+/**

• • v4l2_m2m_try_schedule() - schedule and possibly run a job for any context
• • @m2m_ctx: m2m context
• • Check if this context is ready to queue a job. If suitable,
• • run the next queued job on the mem2mem device.
• • This function shouldn't run in interrupt context.
• • Note that v4l2_m2m_try_schedule() can schedule one job for this context,
• • and then run another job for another context.
• */

+void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +{

• struct v4l2_m2m_dev *m2m_dev = m2m_ctx->m2m_dev;

• __v4l2_m2m_try_queue(m2m_dev, m2m_ctx);

Why introduce __v4l2_m2m_try_queue? Why not keep it in here?

...

v4l2_m2m_try_run(m2m_dev);

I'm completely confused: v4l2_m2m_try_schedule() already calls v4l2_m2m_try_run()!

Either my brain has crashed due to the heatwave I'm suffering through, or there is something amiss with this patch.

Regards,

Hans

...

} EXPORT_SYMBOL_GPL(v4l2_m2m_try_schedule);

Regards,

Hans

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On 27/07/18 17:16, Ezequiel Garcia wrote:

On Fri, 2018-07-27 at 15:41 +0200, Hans Verkuil wrote:

...

On 27/07/18 15:35, Hans Verkuil wrote:

...

On 25/07/18 19:15, Ezequiel Garcia wrote:

...

Commit 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") removed a redundant call to v4l2_m2m_try_run but instead introduced a bug. Consider the following case:

1. Context A schedules, queues and runs job A.
2. While the m2m device is running, context B schedules and queues job B. Job B cannot run, because it has to wait for job A.
3. Job A completes, calls v4l2_m2m_job_finish, and tries to queue a job for context A, but since the context is empty it won't do anything.

In this scenario, queued job B will never run. Fix this by calling v4l2_m2m_try_run from v4l2_m2m_try_schedule.

While here, add more documentation to these functions.

Fixes: 34dbb848d5e4 ("media: mem2mem: Remove excessive try_run call") Signed-off-by: Ezequiel Garcia ezequiel@collabora.com

So just to be clear: this first patch fixes a regression and can be applied separately from the other patches?

That is correct, it's a regression and can be applied independently.

This patch has been tested independently of the rest of the series, using the test introduced in "selftests: media_tests: Add a memory-to-memory concurrent stress test".

Without this patch, the test fails.

...

...

...

---

drivers/media/v4l2-core/v4l2-mem2mem.c | 32 +++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c index 5f9cd5b74cda..dfd796621b06 100644 --- a/drivers/media/v4l2-core/v4l2-mem2mem.c +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c @@ -209,15 +209,23 @@ static void v4l2_m2m_try_run(struct v4l2_m2m_dev *m2m_dev) m2m_dev->curr_ctx->job_flags |= TRANS_RUNNING; spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);

• dprintk("Running job on m2m_ctx: %p\n", m2m_dev->curr_ctx);

Is this intended? It feels out of place in this patch.

It was intended :) Since the patch is adding some more documentation, it felt OK to add this debug message, as it also helps the testing.

But I can drop it if you think it's out of place.

...

...

...

m2m_dev->m2m_ops->device_run(m2m_dev->curr_ctx->priv); } -void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +/*

• • __v4l2_m2m_try_queue() - queue a job
• • @m2m_dev: m2m device
• • @m2m_ctx: m2m context
• • Check if this context is ready to queue a job.
• • This function can run in interrupt context.
• */

+static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev, struct v4l2_m2m_ctx *m2m_ctx) {

• struct v4l2_m2m_dev *m2m_dev; unsigned long flags_job, flags_out, flags_cap;

• m2m_dev = m2m_ctx->m2m_dev; dprintk("Trying to schedule a job for m2m_ctx: %p\n", m2m_ctx);

if (!m2m_ctx->out_q_ctx.q.streaming @@ -275,7 +283,25 @@ void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) m2m_ctx->job_flags |= TRANS_QUEUED; spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags_job); +}

+/**

• • v4l2_m2m_try_schedule() - schedule and possibly run a job for any context
• • @m2m_ctx: m2m context
• • Check if this context is ready to queue a job. If suitable,
• • run the next queued job on the mem2mem device.
• • This function shouldn't run in interrupt context.
• • Note that v4l2_m2m_try_schedule() can schedule one job for this context,
• • and then run another job for another context.
• */

+void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx *m2m_ctx) +{

• struct v4l2_m2m_dev *m2m_dev = m2m_ctx->m2m_dev;

• __v4l2_m2m_try_queue(m2m_dev, m2m_ctx);

Why introduce __v4l2_m2m_try_queue? Why not keep it in here?

Well, specifically we need to make sure xxx_try_run is called even if no job was queued. After a lot of back and forth, I ended up thinking the queue and run operations were different and needed different functions.

If we were to keep the code in try_schedule, we would have to use some extra conditionals or gotos to make sure try_run is called even if no job was queued.

The important thing to keep in mind here is that these functions could be called on a given context, but then actually run a job for another context.

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v4l2_m2m_try_run(m2m_dev);

I'm completely confused: v4l2_m2m_try_schedule() already calls v4l2_m2m_try_run()!

Either my brain has crashed due to the heatwave I'm suffering through, or there is something amiss with this patch.

Right, v4l2_m2m_try_schedule calls v4l2_m2m_try_run *if* a job was queued. This might not always be the case.

Consider you schedule two jobs, both will be queued but only one will run. When will the second job run? Answer: never :)

Ah, now I get it. I hadn't seen that the 'return' statements in try_schedule would prevent the try_run call at the end.

Thanks for the patch, I'll make a pull request for this one.

Regards,

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