[PATCH v5 10/16] media: platform: Add mali-c55 3a stats devnode
Dan Scally
dan.scally at ideasonboard.com
Mon Jul 1 08:12:12 PDT 2024
Hi Laurent
On 29/06/2024 16:04, Laurent Pinchart wrote:
> Hi Dan,
>
> On Thu, Jun 20, 2024 at 04:10:01PM +0100, Daniel Scally wrote:
>> On 16/06/2024 22:19, Laurent Pinchart wrote:
>>> On Wed, May 29, 2024 at 04:28:52PM +0100, Daniel Scally wrote:
>>>> Add a new code file to govern the 3a statistics capture node.
>>>>
>>>> Acked-by: Nayden Kanchev <nayden.kanchev at arm.com>
>>>> Co-developed-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
>>>> Signed-off-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
>>>> Signed-off-by: Daniel Scally <dan.scally at ideasonboard.com>
>>>> ---
>>>> Changes in v5:
>>>>
>>>> - New patch
>>>>
>>>> drivers/media/platform/arm/mali-c55/Makefile | 3 +-
>>>> .../platform/arm/mali-c55/mali-c55-common.h | 28 ++
>>>> .../platform/arm/mali-c55/mali-c55-core.c | 15 +
>>>> .../platform/arm/mali-c55/mali-c55-isp.c | 1 +
>>>> .../arm/mali-c55/mali-c55-registers.h | 3 +
>>>> .../platform/arm/mali-c55/mali-c55-stats.c | 350 ++++++++++++++++++
>>>> 6 files changed, 399 insertions(+), 1 deletion(-)
>>>> create mode 100644 drivers/media/platform/arm/mali-c55/mali-c55-stats.c
>>>>
>>>> diff --git a/drivers/media/platform/arm/mali-c55/Makefile b/drivers/media/platform/arm/mali-c55/Makefile
>>>> index 77dcb2fbf0f4..cd5a64bf0c62 100644
>>>> --- a/drivers/media/platform/arm/mali-c55/Makefile
>>>> +++ b/drivers/media/platform/arm/mali-c55/Makefile
>>>> @@ -4,6 +4,7 @@ mali-c55-y := mali-c55-capture.o \
>>>> mali-c55-core.o \
>>>> mali-c55-isp.o \
>>>> mali-c55-tpg.o \
>>>> - mali-c55-resizer.o
>>>> + mali-c55-resizer.o \
>>>> + mali-c55-stats.o
>>>>
>>>> obj-$(CONFIG_VIDEO_MALI_C55) += mali-c55.o
>>>> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-common.h b/drivers/media/platform/arm/mali-c55/mali-c55-common.h
>>>> index 2d0c4d152beb..44119e04009b 100644
>>>> --- a/drivers/media/platform/arm/mali-c55/mali-c55-common.h
>>>> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-common.h
>>>> @@ -79,6 +79,7 @@ enum mali_c55_isp_pads {
>>>> MALI_C55_ISP_PAD_SINK_VIDEO,
>>>> MALI_C55_ISP_PAD_SOURCE,
>>>> MALI_C55_ISP_PAD_SOURCE_BYPASS,
>>>> + MALI_C55_ISP_PAD_SOURCE_3A,
>>> Functions and structures are named with a "stats" suffix, let's call
>>> this MALI_C55_ISP_PAD_SOURCE_STATS.
>>>
>>>> MALI_C55_ISP_NUM_PADS,
>>>> };
>>>>
>>>> @@ -194,6 +195,28 @@ struct mali_c55_cap_dev {
>>>> bool streaming;
>>>> };
>>>>
>>>> +struct mali_c55_stats_buf {
>>>> + struct vb2_v4l2_buffer vb;
>>>> + spinlock_t lock;
>>> All locks require a comment to document what they protect. Same below.
>>>
>>>> + unsigned int segments_remaining;
>>>> + struct list_head queue;
>>>> + bool failed;
>>>> +};
>>>> +
>>>> +struct mali_c55_stats {
>>>> + struct mali_c55 *mali_c55;
>>>> + struct video_device vdev;
>>>> + struct dma_chan *channel;
>>>> + struct vb2_queue queue;
>>>> + struct media_pad pad;
>>>> + struct mutex lock;
>>>> +
>>>> + struct {
>>>> + spinlock_t lock;
>>>> + struct list_head queue;
>>>> + } buffers;
>>>> +};
>>>> +
>>>> enum mali_c55_config_spaces {
>>>> MALI_C55_CONFIG_PING,
>>>> MALI_C55_CONFIG_PONG,
>>>> @@ -224,6 +247,7 @@ struct mali_c55 {
>>>> struct mali_c55_isp isp;
>>>> struct mali_c55_resizer resizers[MALI_C55_NUM_RZRS];
>>>> struct mali_c55_cap_dev cap_devs[MALI_C55_NUM_CAP_DEVS];
>>>> + struct mali_c55_stats stats;
>>>>
>>>> struct list_head contexts;
>>>> enum mali_c55_config_spaces next_config;
>>>> @@ -245,6 +269,8 @@ int mali_c55_register_resizers(struct mali_c55 *mali_c55);
>>>> void mali_c55_unregister_resizers(struct mali_c55 *mali_c55);
>>>> int mali_c55_register_capture_devs(struct mali_c55 *mali_c55);
>>>> void mali_c55_unregister_capture_devs(struct mali_c55 *mali_c55);
>>>> +int mali_c55_register_stats(struct mali_c55 *mali_c55);
>>>> +void mali_c55_unregister_stats(struct mali_c55 *mali_c55);
>>>> struct mali_c55_ctx *mali_c55_get_active_context(struct mali_c55 *mali_c55);
>>>> void mali_c55_set_plane_done(struct mali_c55_cap_dev *cap_dev,
>>>> enum mali_c55_planes plane);
>>>> @@ -262,5 +288,7 @@ mali_c55_isp_fmt_next(const struct mali_c55_isp_fmt *fmt);
>>>> bool mali_c55_isp_is_format_supported(unsigned int mbus_code);
>>>> #define for_each_mali_isp_fmt(fmt)\
>>>> for ((fmt) = NULL; ((fmt) = mali_c55_isp_fmt_next((fmt)));)
>>>> +void mali_c55_stats_fill_buffer(struct mali_c55 *mali_c55,
>>>> + enum mali_c55_config_spaces cfg_space);
>>>>
>>>> #endif /* _MALI_C55_COMMON_H */
>>>> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-core.c b/drivers/media/platform/arm/mali-c55/mali-c55-core.c
>>>> index 50caf5ee7474..9ea70010876c 100644
>>>> --- a/drivers/media/platform/arm/mali-c55/mali-c55-core.c
>>>> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-core.c
>>>> @@ -337,6 +337,16 @@ static int mali_c55_create_links(struct mali_c55 *mali_c55)
>>>> }
>>>> }
>>>>
>>>> + ret = media_create_pad_link(&mali_c55->isp.sd.entity,
>>>> + MALI_C55_ISP_PAD_SOURCE_3A,
>>>> + &mali_c55->stats.vdev.entity, 0,
>>>> + MEDIA_LNK_FL_ENABLED | MEDIA_LNK_FL_IMMUTABLE);
>>>> + if (ret) {
>>>> + dev_err(mali_c55->dev,
>>>> + "failed to link ISP and 3a stats node\n");
>>> s/3a stats/stats/
>>>
>>>> + goto err_remove_links;
>>>> + }
>>>> +
>>>> return 0;
>>>>
>>>> err_remove_links:
>>>> @@ -350,6 +360,7 @@ static void mali_c55_unregister_entities(struct mali_c55 *mali_c55)
>>>> mali_c55_unregister_isp(mali_c55);
>>>> mali_c55_unregister_resizers(mali_c55);
>>>> mali_c55_unregister_capture_devs(mali_c55);
>>>> + mali_c55_unregister_stats(mali_c55);
>>>> }
>>>>
>>>> static int mali_c55_register_entities(struct mali_c55 *mali_c55)
>>>> @@ -372,6 +383,10 @@ static int mali_c55_register_entities(struct mali_c55 *mali_c55)
>>>> if (ret)
>>>> goto err_unregister_entities;
>>>>
>>>> + ret = mali_c55_register_stats(mali_c55);
>>>> + if (ret)
>>>> + goto err_unregister_entities;
>>>> +
>>>> ret = mali_c55_create_links(mali_c55);
>>>> if (ret)
>>>> goto err_unregister_entities;
>>>> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-isp.c b/drivers/media/platform/arm/mali-c55/mali-c55-isp.c
>>>> index ea8b7b866e7a..94876fba3353 100644
>>>> --- a/drivers/media/platform/arm/mali-c55/mali-c55-isp.c
>>>> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-isp.c
>>>> @@ -564,6 +564,7 @@ int mali_c55_register_isp(struct mali_c55 *mali_c55)
>>>> isp->pads[MALI_C55_ISP_PAD_SINK_VIDEO].flags = MEDIA_PAD_FL_SINK;
>>>> isp->pads[MALI_C55_ISP_PAD_SOURCE].flags = MEDIA_PAD_FL_SOURCE;
>>>> isp->pads[MALI_C55_ISP_PAD_SOURCE_BYPASS].flags = MEDIA_PAD_FL_SOURCE;
>>>> + isp->pads[MALI_C55_ISP_PAD_SOURCE_3A].flags = MEDIA_PAD_FL_SOURCE;
>>>>
>>>> ret = media_entity_pads_init(&sd->entity, MALI_C55_ISP_NUM_PADS,
>>>> isp->pads);
>>>> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-registers.h b/drivers/media/platform/arm/mali-c55/mali-c55-registers.h
>>>> index cb27abde2aa5..eb3719245ec3 100644
>>>> --- a/drivers/media/platform/arm/mali-c55/mali-c55-registers.h
>>>> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-registers.h
>>>> @@ -68,6 +68,9 @@
>>>> #define MALI_C55_VC_START(v) ((v) & 0xffff)
>>>> #define MALI_C55_VC_SIZE(v) (((v) & 0xffff) << 16)
>>>>
>>>> +#define MALI_C55_REG_1024BIN_HIST 0x054a8
>>>> +#define MALI_C55_1024BIN_HIST_SIZE 4096
>>>> +
>>>> /* Ping/Pong Configuration Space */
>>>> #define MALI_C55_REG_BASE_ADDR 0x18e88
>>>> #define MALI_C55_REG_BYPASS_0 0x18eac
>>>> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-stats.c b/drivers/media/platform/arm/mali-c55/mali-c55-stats.c
>>>> new file mode 100644
>>>> index 000000000000..aa40480ed814
>>>> --- /dev/null
>>>> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-stats.c
>>>> @@ -0,0 +1,350 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * ARM Mali-C55 ISP Driver - 3A Statistics capture device
>>>> + *
>>>> + * Copyright (C) 2023 Ideas on Board Oy
>>>> + */
>>>> +
>>>> +#include <linux/dmaengine.h>
>>>> +#include <linux/media/arm/mali-c55-config.h>
>>>> +#include <linux/spinlock.h>
>>> You're missing some headers here, for
>>>
>>> container_of()
>>> dev_err()
>>> list_*()
>>> mutex_init()
>>> strscpy()
>>> strscpy()
>>>
>>>> +
>>>> +#include <media/media-entity.h>
>>>> +#include <media/v4l2-dev.h>
>>>> +#include <media/v4l2-event.h>
>>>> +#include <media/v4l2-fh.h>
>>>> +#include <media/v4l2-ioctl.h>
>>>> +#include <media/videobuf2-core.h>
>>>> +#include <media/videobuf2-dma-contig.h>
>>>> +
>>>> +#include "mali-c55-common.h"
>>>> +#include "mali-c55-registers.h"
>>>> +
>>>> +static unsigned int metering_space_addrs[] = {
>>> const
>>>
>>>> + [MALI_C55_CONFIG_PING] = 0x095AC,
>>>> + [MALI_C55_CONFIG_PONG] = 0x2156C,
>>> Lower-case hex constants.
>>>
>>>> +};
>>>> +
>>>> +static int mali_c55_stats_enum_fmt_meta_cap(struct file *file, void *fh,
>>>> + struct v4l2_fmtdesc *f)
>>>> +{
>>>> + if (f->index || f->type != V4L2_BUF_TYPE_META_CAPTURE)
>>>> + return -EINVAL;
>>>> +
>>>> + f->pixelformat = V4L2_META_FMT_MALI_C55_3A_STATS;
>>> The format could be called V4L2_META_FMT_MALI_C55_STATS. While most
>>> statistics are related to one of the 3A algorithms, I think it would be
>>> better to name this generically. It's name bikeshedding only of course.
>>>
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static int mali_c55_stats_g_fmt_meta_cap(struct file *file, void *fh,
>>>> + struct v4l2_format *f)
>>>> +{
>>>> + static const struct v4l2_meta_format mfmt = {
>>>> + .dataformat = V4L2_META_FMT_MALI_C55_3A_STATS,
>>>> + .buffersize = sizeof(struct mali_c55_stats_buffer)
>>>> + };
>>>> +
>>>> + if (f->type != V4L2_BUF_TYPE_META_CAPTURE)
>>>> + return -EINVAL;
>>>> +
>>>> + f->fmt.meta = mfmt;
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static int mali_c55_stats_querycap(struct file *file,
>>>> + void *priv, struct v4l2_capability *cap)
>>>> +{
>>>> + strscpy(cap->driver, MALI_C55_DRIVER_NAME, sizeof(cap->driver));
>>>> + strscpy(cap->card, "ARM Mali-C55 ISP", sizeof(cap->card));
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static const struct v4l2_ioctl_ops mali_c55_stats_v4l2_ioctl_ops = {
>>>> + .vidioc_reqbufs = vb2_ioctl_reqbufs,
>>>> + .vidioc_querybuf = vb2_ioctl_querybuf,
>>>> + .vidioc_create_bufs = vb2_ioctl_create_bufs,
>>>> + .vidioc_qbuf = vb2_ioctl_qbuf,
>>>> + .vidioc_expbuf = vb2_ioctl_expbuf,
>>>> + .vidioc_dqbuf = vb2_ioctl_dqbuf,
>>>> + .vidioc_prepare_buf = vb2_ioctl_prepare_buf,
>>>> + .vidioc_streamon = vb2_ioctl_streamon,
>>>> + .vidioc_streamoff = vb2_ioctl_streamoff,
>>>> + .vidioc_enum_fmt_meta_cap = mali_c55_stats_enum_fmt_meta_cap,
>>>> + .vidioc_g_fmt_meta_cap = mali_c55_stats_g_fmt_meta_cap,
>>>> + .vidioc_s_fmt_meta_cap = mali_c55_stats_g_fmt_meta_cap,
>>>> + .vidioc_try_fmt_meta_cap = mali_c55_stats_g_fmt_meta_cap,
>>>> + .vidioc_querycap = mali_c55_stats_querycap,
>>>> + .vidioc_subscribe_event = v4l2_ctrl_subscribe_event,
>>>> + .vidioc_unsubscribe_event = v4l2_event_unsubscribe,
>>>> +};
>>>> +
>>>> +static const struct v4l2_file_operations mali_c55_stats_v4l2_fops = {
>>>> + .owner = THIS_MODULE,
>>>> + .unlocked_ioctl = video_ioctl2,
>>>> + .open = v4l2_fh_open,
>>>> + .release = vb2_fop_release,
>>>> + .poll = vb2_fop_poll,
>>>> + .mmap = vb2_fop_mmap,
>>>> +};
>>>> +
>>>> +static int
>>>> +mali_c55_stats_queue_setup(struct vb2_queue *q, unsigned int *num_buffers,
>>>> + unsigned int *num_planes, unsigned int sizes[],
>>>> + struct device *alloc_devs[])
>>>> +{
>>>> + struct mali_c55_stats *stats = vb2_get_drv_priv(q);
>>>> +
>>>> + if (*num_planes && *num_planes > 1)
>>>> + return -EINVAL;
>>>> +
>>>> + if (sizes[0] && sizes[0] != sizeof(struct mali_c55_stats_buffer))
>>>> + return -EINVAL;
>>>> +
>>>> + *num_planes = 1;
>>>> + sizes[0] = sizeof(struct mali_c55_stats_buffer);
>>>> +
>>>> + if (stats->channel)
>>>> + alloc_devs[0] = stats->channel->device->dev;
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static void mali_c55_stats_buf_queue(struct vb2_buffer *vb)
>>>> +{
>>>> + struct mali_c55_stats *stats = vb2_get_drv_priv(vb->vb2_queue);
>>>> + struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
>>>> + struct mali_c55_stats_buf *buf = container_of(vbuf,
>>>> + struct mali_c55_stats_buf, vb);
>>>> +
>>>> + vb2_set_plane_payload(vb, 0, sizeof(struct mali_c55_stats_buffer));
>>>> + buf->segments_remaining = 2;
>>>> + buf->failed = false;
>>>> +
>>>> + spin_lock(&stats->buffers.lock);
>>> Isn't the DMA completion handler run from IRQ context ? If so you'll
>>> need to use spin_lock_irq() here and in the other function that are
>>> not called with interrupts disabled.
>> They're run in the bottom half of the interrupt handler; I'm under the
>> impression that that means the interrupts aren't disabled, and it's
>> safe to do...is that mistaken?
> I'm talking about the DMA completion handler, called by the DMA engine
> subsystem, not the IRQs of the C55 itself.
Ah! I follow you now sorry. Hm, that's an interesting thought...I think for the PL330 the answer is
no; the interrupt handler wakes a thread that runs the callbacks for any DMA transfers that are
completed...I don't know that that's a design rule we can rely on though so possibly it's better to
be safe. Is there a disadvantage to using spin_lock_irq() outside of IRQ context?
>
>>>> + list_add_tail(&buf->queue, &stats->buffers.queue);
>>>> + spin_unlock(&stats->buffers.lock);
>>>> +}
>>>> +
>>>> +static void mali_c55_stats_stop_streaming(struct vb2_queue *q)
>>>> +{
>>>> + struct mali_c55_stats *stats = vb2_get_drv_priv(q);
>>>> + struct mali_c55_stats_buf *buf, *tmp;
>>>> +
>>>> + spin_lock(&stats->buffers.lock);
>>>> +
>>>> + list_for_each_entry_safe(buf, tmp, &stats->buffers.queue, queue) {
>>>> + list_del(&buf->queue);
>>>> + vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
>>>> + }
>>>> +
>>>> + spin_unlock(&stats->buffers.lock);
>>>> +}
>>>> +
>>>> +static const struct vb2_ops mali_c55_stats_vb2_ops = {
>>>> + .queue_setup = mali_c55_stats_queue_setup,
>>>> + .buf_queue = mali_c55_stats_buf_queue,
>>>> + .wait_prepare = vb2_ops_wait_prepare,
>>>> + .wait_finish = vb2_ops_wait_finish,
>>>> + .stop_streaming = mali_c55_stats_stop_streaming,
>>>> +};
>>>> +
>>>> +static void
>>>> +mali_c55_stats_metering_complete(void *param,
>>>> + const struct dmaengine_result *result)
>>>> +{
>>>> + struct mali_c55_stats_buf *buf = param;
>>>> +
>>>> + spin_lock(&buf->lock);
>>> I wonder if this is needed. Can the DMA engine call the completion
>>> handlers of two sequential DMA transfers in parallel ?
>> The DMA engine that's on the system we have can't...I wasn't sure
>> whether that was generically true.
> I think it is, but please double-check.
>
>>>> +
>>>> + if (buf->failed)
>>>> + goto out_unlock;
>>>> +
>>>> + buf->vb.vb2_buf.timestamp = ktime_get_boottime_ns();
>>>> +
>>>> + if (result->result != DMA_TRANS_NOERROR) {
>>>> + buf->failed = true;
>>>> + vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
>>> This will possibly return the buffer to userspace after the first DMA
>>> transfer. Userspace could then requeue the buffer to the kernel before
>>> the completion of the second DMA transfer. That will cause trouble. I
>>> think you should instead do something like
>>>
>>> spin_lock(&buf->lock);
>>>
>>> if (result->result != DMA_TRANS_NOERROR)
>>> buf->failed = true;
>>>
>>> if (!--buf->segments_remaining) {
>>> buf->vb.vb2_buf.timestamp = ktime_get_boottime_ns();
>>> vb2_buffer_done(&buf->vb.vb2_buf, buf->failed ?
>>> VB2_BUF_STATE_ERROR : VB2_BUF_STATE_DONE);
>>> }
>>>
>>> spin_unlock(&buf->lock);
>>>
>>> The
>>>
>>> buf->vb.vb2_buf.timestamp = ktime_get_boottime_ns();
>>>
>>> line could also be moved to mali_c55_stats_fill_buffer(), which would
>>> make sure the timestamp is filled in case of DMA submission failures.
>> Okedokey
>>
>>>> + goto out_unlock;
>>>> + }
>>>> +
>>>> + if (!--buf->segments_remaining)
>>>> + vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_DONE);
>>>> +
>>>> +out_unlock:
>>>> + spin_unlock(&buf->lock);
>>>> +}
>>>> +
>>>> +static int mali_c55_stats_dma_xfer(struct mali_c55_stats *stats, dma_addr_t src,
>>>> + dma_addr_t dst,
>>>> + struct mali_c55_stats_buf *buf,
>>>> + size_t length,
>>>> + void (*callback)(void *, const struct dmaengine_result *result))
>>> The same callback is used for both invocations of this function, you can
>>> drop the parameter and hardcode it below.
>> Yeah, not even sure now why I had a parameter.
>>
>>>> +{
>>>> + struct dma_async_tx_descriptor *tx;
>>>> + dma_cookie_t cookie;
>>>> +
>>>> + tx = dmaengine_prep_dma_memcpy(stats->channel, dst, src, length, 0);
>>>> + if (!tx) {
>>>> + dev_err(stats->mali_c55->dev, "failed to prep stats DMA\n");
>>>> + return -EIO;
>>>> + }
>>>> +
>>>> + tx->callback_result = callback;
>>>> + tx->callback_param = buf;
>>>> +
>>>> + cookie = dmaengine_submit(tx);
>>>> + if (dma_submit_error(cookie)) {
>>>> + dev_err(stats->mali_c55->dev, "failed to submit stats DMA\n");
>>>> + return -EIO;
>>>> + }
>>>> +
>>>> + dma_async_issue_pending(stats->channel);
>>>> + return 0;
>>>> +}
>>>> +
>>>> +void mali_c55_stats_fill_buffer(struct mali_c55 *mali_c55,
>>>> + enum mali_c55_config_spaces cfg_space)
>>>> +{
>>>> + struct mali_c55_ctx *ctx = mali_c55_get_active_context(mali_c55);
>>>> + struct mali_c55_stats *stats = &mali_c55->stats;
>>>> + struct mali_c55_stats_buf *buf = NULL;
>>>> + dma_addr_t src, dst;
>>>> + int ret;
>>>> +
>>>> + spin_lock(&stats->buffers.lock);
>>>> + if (!list_empty(&stats->buffers.queue)) {
>>>> + buf = list_first_entry(&stats->buffers.queue,
>>>> + struct mali_c55_stats_buf, queue);
>>>> + list_del(&buf->queue);
>>>> + }
>>>> + spin_unlock(&stats->buffers.lock);
>>>> +
>>>> + if (!buf)
>>>> + return;
>>>> +
>>>> + buf->vb.sequence = mali_c55->isp.frame_sequence;
>>>> +
>>>> + /*
>>>> + * There are infact two noncontiguous sections of the ISP's
>>> s/infact/in fact/
>>>
>>>> + * memory space that hold statistics for 3a algorithms to use. A
>>> s/use. A/use: a/
>>>
>>>> + * section in each config space and a global section holding
>>>> + * histograms which is double buffered and so holds data for the
>>>> + * last frame. We need to read both.
>>>> + */
>>>> + src = ctx->base + MALI_C55_REG_1024BIN_HIST;
>>>> + dst = vb2_dma_contig_plane_dma_addr(&buf->vb.vb2_buf, 0);
>>>> +
>>>> + ret = mali_c55_stats_dma_xfer(stats, src, dst, buf,
>>>> + MALI_C55_1024BIN_HIST_SIZE,
>>>> + mali_c55_stats_metering_complete);
>>>> + if (ret)
>>>> + goto err_fail_buffer;
>>>> +
>>>> + src = ctx->base + metering_space_addrs[cfg_space];
>>>> + dst += MALI_C55_1024BIN_HIST_SIZE;
>>>> +
>>>> + ret = mali_c55_stats_dma_xfer(
>>>> + stats, src, dst, buf,
>>>> + sizeof(struct mali_c55_stats_buffer) - MALI_C55_1024BIN_HIST_SIZE,
>>>> + mali_c55_stats_metering_complete);
>>>> + if (ret) {
>>>> + dmaengine_terminate_sync(stats->channel);
>>>> + goto err_fail_buffer;
>>>> + }
>>> I think you will need to terminate DMA transfers at stream off time.
>>>
>>>> +
>>>> + return;
>>>> +
>>>> +err_fail_buffer:
>>>> + vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
>>>> +}
>>>> +
>>>> +void mali_c55_unregister_stats(struct mali_c55 *mali_c55)
>>>> +{
>>>> + struct mali_c55_stats *stats = &mali_c55->stats;
>>>> +
>>>> + if (!video_is_registered(&stats->vdev))
>>>> + return;
>>>> +
>>>> + vb2_video_unregister_device(&stats->vdev);
>>>> + media_entity_cleanup(&stats->vdev.entity);
>>>> + dma_release_channel(stats->channel);
>>>> + mutex_destroy(&stats->lock);
>>>> +}
>>>> +
>>>> +int mali_c55_register_stats(struct mali_c55 *mali_c55)
>>>> +{
>>>> + struct mali_c55_stats *stats = &mali_c55->stats;
>>>> + struct video_device *vdev = &stats->vdev;
>>>> + struct vb2_queue *vb2q = &stats->queue;
>>>> + dma_cap_mask_t mask;
>>>> + int ret;
>>>> +
>>>> + mutex_init(&stats->lock);
>>>> + INIT_LIST_HEAD(&stats->buffers.queue);
>>>> +
>>>> + dma_cap_zero(mask);
>>>> + dma_cap_set(DMA_MEMCPY, mask);
>>>> +
>>>> + stats->channel = dma_request_channel(mask, 0, NULL);
>>> Do we need a CPU fallback in case no DMA is available ?
>> Yes, actually.
>>
>>> I'm still very curious to know how long it takes to perform the DMA
>>> transfer, compared to copying the data with the CPU, and especially
>>> compared to the frame duration.
>> On my list of things to test and report :)
> Looking forward to it :-)
>
>>>> + if (!stats->channel) {
>>>> + ret = -ENODEV;
>>>> + goto err_destroy_mutex;
>>>> + }
>>>> +
>>>> + stats->pad.flags = MEDIA_PAD_FL_SINK;
>>>> + ret = media_entity_pads_init(&stats->vdev.entity, 1, &stats->pad);
>>>> + if (ret)
>>>> + goto err_release_dma_channel;
>>>> +
>>>> + vb2q->type = V4L2_BUF_TYPE_META_CAPTURE;
>>>> + vb2q->io_modes = VB2_MMAP | VB2_DMABUF;
>>>> + vb2q->drv_priv = stats;
>>>> + vb2q->mem_ops = &vb2_dma_contig_memops;
>>>> + vb2q->ops = &mali_c55_stats_vb2_ops;
>>>> + vb2q->buf_struct_size = sizeof(struct mali_c55_stats_buf);
>>>> + vb2q->min_queued_buffers = 1;
>>>> + vb2q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>>>> + vb2q->lock = &stats->lock;
>>>> + vb2q->dev = mali_c55->dev;
>>> That's not the right device. The device that performs the DMA operation
>>> is the DMA engine, and that's what you need to pass to vb2. Otherwise
>>> the DMA address returned by vb2_dma_contig_plane_dma_addr() will be
>>> mapped to the ISP device, not the DMA engine. In practice, if neither
>>> are behind an IOMMU, things will likely work, but when that's not the
>>> case, run into problems.
>>>
>>>> +
>>>> + ret = vb2_queue_init(vb2q);
>>>> + if (ret) {
>>>> + dev_err(mali_c55->dev, "stats vb2 queue init failed\n");
>>>> + goto err_cleanup_entity;
>>>> + }
>>>> +
>>>> + strscpy(stats->vdev.name, "mali-c55 3a stats", sizeof(stats->vdev.name));
>>> s/3a //
>>>
>>>> + vdev->release = video_device_release_empty;
>>> That's never right. You should refcount the data structures to ensure
>>> proper lifetime management.
>>>
>>>> + vdev->fops = &mali_c55_stats_v4l2_fops;
>>>> + vdev->ioctl_ops = &mali_c55_stats_v4l2_ioctl_ops;
>>>> + vdev->lock = &stats->lock;
>>>> + vdev->v4l2_dev = &mali_c55->v4l2_dev;
>>>> + vdev->queue = &stats->queue;
>>>> + vdev->device_caps = V4L2_CAP_META_CAPTURE | V4L2_CAP_STREAMING;
>>>> + vdev->vfl_dir = VFL_DIR_RX;
>>>> + video_set_drvdata(vdev, stats);
>>>> +
>>>> + ret = video_register_device(vdev, VFL_TYPE_VIDEO, -1);
>>>> + if (ret) {
>>>> + dev_err(mali_c55->dev,
>>>> + "failed to register stats video device\n");
>>>> + goto err_release_vb2q;
>>>> + }
>>>> +
>>>> + stats->mali_c55 = mali_c55;
>>>> +
>>>> + return 0;
>>>> +
>>>> +err_release_vb2q:
>>>> + vb2_queue_release(vb2q);
>>>> +err_cleanup_entity:
>>>> + media_entity_cleanup(&stats->vdev.entity);
>>>> +err_release_dma_channel:
>>>> + dma_release_channel(stats->channel);
>>>> +err_destroy_mutex:
>>>> + mutex_destroy(&stats->lock);
>>>> +
>>>> + return ret;
>>>> +}
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