Message-ID: <33c54fe5-67a5-496a-87fb-14242c2fd9fd@ideasonboard.com>
Date: Wed, 10 Jan 2024 15:36:35 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Cosmin Tanislav <demonsingur@...il.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Jacopo Mondi <jacopo+renesas@...ndi.org>, Hans de Goede
 <hdegoede@...hat.com>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] media: v4l: implement virtual channels

Hi,

On 10/01/2024 15:27, Cosmin Tanislav wrote:
> Hi, Tomi.
> 
> The usecase for this is crossbar devices that allow for mapping virtual channel
> 
> ids dynamically.
> 
> The remapping happens based on VC and DT. DT can be determined based on
> 
> the pixel code, but VC has no way of being determined at runtime through
> 
> standard V4L2 APIs.

The DT shouldn't be determined based on the pixel code. The DT, and the 
VC, should be queried from the source subdev using the get_frame_desc() 
subdev op.

So, in general, the streams API presents a logical view of the streams 
without a strict direct mapping to the hardware. When the streaming is 
started, the subdev drivers need to figure out the hardware details, 
and, specifically for the DT & VC of incoming streams, can ask details 
from the source subdevice using get_frame_desc().

Or if I misunderstand your case, can you provide a concrete example of 
the pipeline and the media tree in question to help the discussion.

  Tomi

> 
> The alternative would be to hardcode them in device tree, which is not very
> 
> nice, and cannot account for all possible user configurations.
> 
> I'm aware that VC is a bus-specific feature, which is why this is an RFC.
> 
> Having a V4L2 implementation would solve a lot of devices having to
> 
> hardcode VCs.
> 
> 
> On 1/10/24 14:50, Tomi Valkeinen wrote:
>> Hi!
>>
>> On 10/01/2024 14:51, Cosmin Tanislav wrote:
>>> With experimental support for multiple streams per pad being added, the
>>> pieces are in place to support a virtual channel id per stream.
>>>
>>> This is necessary because stream ids cannot be directly mapped to a virtual
>>> channel id, since the same virtual channel id can be assigned to multiple
>>> streams of data, each with a different data type.
>>>
>>> To implement this, the following steps have been taken.
>>>
>>> Add subdev ioctls for getting and setting the virtual channel for a
>>> specific pad and stream.
>>>
>>> Add pad .get_vc() and .set_vc() ops.
>>>
>>> Add the virtual channel to the stream config in V4L2 subdev central state.
>>>
>>> Add a default .get_vc() implementation that retrieves the virtual channel
>>> from the central state, or, if that is not supported, default to virtual
>>> channel 0.
>>
>> Why do you need this?
>>
>> The design idea with streams was that the streams are not tied to CSI-2 streams (or to any specific HW). The CSI-2 virtual channels should be handled by the drivers internally, and they should not be visible to the userspace at all.
>>
>>   Tomi
>>
>>> Signed-off-by: Cosmin Tanislav <demonsingur@...il.com>
>>> ---
>>>    drivers/media/v4l2-core/v4l2-subdev.c | 57 +++++++++++++++++++++++++++
>>>    include/media/v4l2-subdev.h           | 39 ++++++++++++++++++
>>>    include/uapi/linux/v4l2-subdev.h      | 18 +++++++++
>>>    3 files changed, 114 insertions(+)
>>>
>>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
>>> index be86b906c985..8945bfd0fe12 100644
>>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
>>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
>>> @@ -535,6 +535,9 @@ subdev_ioctl_get_state(struct v4l2_subdev *sd, struct v4l2_subdev_fh *subdev_fh,
>>>        case VIDIOC_SUBDEV_S_ROUTING:
>>>            which = ((struct v4l2_subdev_routing *)arg)->which;
>>>            break;
>>> +    case VIDIOC_SUBDEV_G_VC:
>>> +    case VIDIOC_SUBDEV_S_VC:
>>> +        which = ((struct v4l2_subdev_vc *)arg)->which;
>>>        }
>>>          return which == V4L2_SUBDEV_FORMAT_TRY ?
>>> @@ -969,6 +972,26 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
>>>                        routing->which, &krouting);
>>>        }
>>>    +    case VIDIOC_SUBDEV_G_VC: {
>>> +        struct v4l2_subdev_vc *vc = arg;
>>> +
>>> +        if (!client_supports_streams)
>>> +            vc->stream = 0;
>>> +
>>> +        memset(vc->reserved, 0, sizeof(vc->reserved));
>>> +        return v4l2_subdev_call(sd, pad, get_vc, state, vc);
>>> +    }
>>> +
>>> +    case VIDIOC_SUBDEV_S_VC: {
>>> +        struct v4l2_subdev_vc *vc = arg;
>>> +
>>> +        if (!client_supports_streams)
>>> +            vc->stream = 0;
>>> +
>>> +        memset(vc->reserved, 0, sizeof(vc->reserved));
>>> +        return v4l2_subdev_call(sd, pad, set_vc, state, vc);
>>> +    }
>>> +
>>>        case VIDIOC_SUBDEV_G_CLIENT_CAP: {
>>>            struct v4l2_subdev_client_capability *client_cap = arg;
>>>    @@ -1602,6 +1625,20 @@ int v4l2_subdev_get_fmt(struct v4l2_subdev *sd, struct v4l2_subdev_state *state,
>>>    }
>>>    EXPORT_SYMBOL_GPL(v4l2_subdev_get_fmt);
>>>    +int v4l2_subdev_get_vc(struct v4l2_subdev *sd, struct v4l2_subdev_state *state,
>>> +               struct v4l2_subdev_vc *vc)
>>> +{
>>> +    u32 vc_id = 0;
>>> +
>>> +    if (sd->flags & V4L2_SUBDEV_FL_STREAMS)
>>> +        vc_id = v4l2_subdev_state_get_stream_vc(state, vc->pad, vc->stream);
>>> +
>>> +    vc->vc = vc_id;
>>> +
>>> +    return 0;
>>> +}
>>> +EXPORT_SYMBOL_GPL(v4l2_subdev_get_vc);
>>> +
>>>    int v4l2_subdev_set_routing(struct v4l2_subdev *sd,
>>>                    struct v4l2_subdev_state *state,
>>>                    const struct v4l2_subdev_krouting *routing)
>>> @@ -1745,6 +1782,26 @@ v4l2_subdev_state_get_stream_compose(struct v4l2_subdev_state *state,
>>>    }
>>>    EXPORT_SYMBOL_GPL(v4l2_subdev_state_get_stream_compose);
>>>    +u32 v4l2_subdev_state_get_stream_vc(struct v4l2_subdev_state *state,
>>> +                    unsigned int pad, u32 stream)
>>> +{
>>> +    struct v4l2_subdev_stream_configs *stream_configs;
>>> +    unsigned int i;
>>> +
>>> +    lockdep_assert_held(state->lock);
>>> +
>>> +    stream_configs = &state->stream_configs;
>>> +
>>> +    for (i = 0; i < stream_configs->num_configs; ++i) {
>>> +        if (stream_configs->configs[i].pad == pad &&
>>> +            stream_configs->configs[i].stream == stream)
>>> +            return stream_configs->configs[i].vc;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +EXPORT_SYMBOL_GPL(v4l2_subdev_state_get_stream_vc);
>>> +
>>>    int v4l2_subdev_routing_find_opposite_end(const struct v4l2_subdev_krouting *routing,
>>>                          u32 pad, u32 stream, u32 *other_pad,
>>>                          u32 *other_stream)
>>> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
>>> index c1f90c1223a7..ed1fdd79c2bb 100644
>>> --- a/include/media/v4l2-subdev.h
>>> +++ b/include/media/v4l2-subdev.h
>>> @@ -722,6 +722,7 @@ struct v4l2_subdev_stream_config {
>>>        u32 stream;
>>>        bool enabled;
>>>    +    u32 vc;
>>>        struct v4l2_mbus_framefmt fmt;
>>>        struct v4l2_rect crop;
>>>        struct v4l2_rect compose;
>>> @@ -858,6 +859,12 @@ struct v4l2_subdev_pad_ops {
>>>        int (*set_fmt)(struct v4l2_subdev *sd,
>>>                   struct v4l2_subdev_state *state,
>>>                   struct v4l2_subdev_format *format);
>>> +    int (*get_vc)(struct v4l2_subdev *sd,
>>> +              struct v4l2_subdev_state *state,
>>> +              struct v4l2_subdev_vc *vc);
>>> +    int (*set_vc)(struct v4l2_subdev *sd,
>>> +              struct v4l2_subdev_state *state,
>>> +              struct v4l2_subdev_vc *vc);
>>>        int (*get_selection)(struct v4l2_subdev *sd,
>>>                     struct v4l2_subdev_state *state,
>>>                     struct v4l2_subdev_selection *sel);
>>> @@ -1494,6 +1501,23 @@ v4l2_subdev_lock_and_get_active_state(struct v4l2_subdev *sd)
>>>    int v4l2_subdev_get_fmt(struct v4l2_subdev *sd, struct v4l2_subdev_state *state,
>>>                struct v4l2_subdev_format *format);
>>>    +/**
>>> + * v4l2_subdev_get_vc() - Fill virtual channel based on state
>>> + * @sd: subdevice
>>> + * @state: subdevice state
>>> + * @vc: pointer to &struct v4l2_subdev_vc
>>> + *
>>> + * Fill @vc->vc field based on the information in the @vc struct.
>>> + *
>>> + * This function can be used by the subdev drivers which support active state to
>>> + * implement v4l2_subdev_pad_ops.get_vc if the subdev driver does not need to
>>> + * do anything special in their get_vc op.
>>> + *
>>> + * Returns 0 on success, error value otherwise.
>>> + */
>>> +int v4l2_subdev_get_vc(struct v4l2_subdev *sd, struct v4l2_subdev_state *state,
>>> +               struct v4l2_subdev_vc *vc);
>>> +
>>>    /**
>>>     * v4l2_subdev_set_routing() - Set given routing to subdev state
>>>     * @sd: The subdevice
>>> @@ -1585,6 +1609,21 @@ struct v4l2_rect *
>>>    v4l2_subdev_state_get_stream_compose(struct v4l2_subdev_state *state,
>>>                         unsigned int pad, u32 stream);
>>>    +/**
>>> + * v4l2_subdev_state_get_stream_vc() - Get the virtual channel of a stream
>>> + * @state: subdevice state
>>> + * @pad: pad id
>>> + * @stream: stream id
>>> + *
>>> + * This returns the virtual channel for the given pad + stream in the
>>> + * subdev state.
>>> + *
>>> + * If the state does not contain the given pad + stream, 0 is returned.
>>> + */
>>> +u32
>>> +v4l2_subdev_state_get_stream_vc(struct v4l2_subdev_state *state,
>>> +                unsigned int pad, u32 stream);
>>> +
>>>    /**
>>>     * v4l2_subdev_routing_find_opposite_end() - Find the opposite stream
>>>     * @routing: routing used to find the opposite side
>>> diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h
>>> index b383c2fe0cf3..8e90405bb1e6 100644
>>> --- a/include/uapi/linux/v4l2-subdev.h
>>> +++ b/include/uapi/linux/v4l2-subdev.h
>>> @@ -187,6 +187,22 @@ struct v4l2_subdev_capability {
>>>        __u32 reserved[14];
>>>    };
>>>    +/**
>>> + * struct v4l2_subdev_vc - Pad-level virtual channel settings
>>> + * @which: format type (from enum v4l2_subdev_format_whence)
>>> + * @pad: pad number, as reported by the media API
>>> + * @vc: virtual channel
>>> + * @stream: stream number, defined in subdev routing
>>> + * @reserved: drivers and applications must zero this array
>>> + */
>>> +struct v4l2_subdev_vc {
>>> +    __u32 which;
>>> +    __u32 pad;
>>> +    __u32 vc;
>>> +    __u32 stream;
>>> +    __u32 reserved[7];
>>> +};
>>> +
>>>    /* The v4l2 sub-device video device node is registered in read-only mode. */
>>>    #define V4L2_SUBDEV_CAP_RO_SUBDEV        0x00000001
>>>    @@ -268,6 +284,8 @@ struct v4l2_subdev_client_capability {
>>>    #define VIDIOC_SUBDEV_S_SELECTION        _IOWR('V', 62, struct v4l2_subdev_selection)
>>>    #define VIDIOC_SUBDEV_G_ROUTING            _IOWR('V', 38, struct v4l2_subdev_routing)
>>>    #define VIDIOC_SUBDEV_S_ROUTING            _IOWR('V', 39, struct v4l2_subdev_routing)
>>> +#define VIDIOC_SUBDEV_G_VC            _IOWR('V', 40, struct v4l2_subdev_vc)
>>> +#define VIDIOC_SUBDEV_S_VC            _IOWR('V', 41, struct v4l2_subdev_vc)
>>>    #define VIDIOC_SUBDEV_G_CLIENT_CAP        _IOR('V',  101, struct v4l2_subdev_client_capability)
>>>    #define VIDIOC_SUBDEV_S_CLIENT_CAP        _IOWR('V',  102, struct v4l2_subdev_client_capability)
>>>    
>>

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