linux-kernel - Re: [PATCH v2 0/3] media: add v4l2_pipeline_stream

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Date:   Tue, 7 Apr 2020 21:36:15 +0200
From:   Niklas Söderlund 
        <niklas.soderlund@...natech.se>
To:     Helen Koike <helen.koike@...labora.com>
Cc:     linux-media@...r.kernel.org, kernel@...labora.com,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        hans.verkuil@...co.com, skhan@...uxfoundation.org,
        mchehab@...nel.org
Subject: Re: [PATCH v2 0/3] media: add v4l2_pipeline_stream_{enable,disable}
 helpers

Hi Helen,

On 2020-04-03 18:33:09 -0300, Helen Koike wrote:
> Hi,
> 
> Media drivers need to iterate through the pipeline and call .s_stream()
> callbacks in the subdevices.
> 
> Instead of repeating code, add helpers for this.
> 
> These helpers will go walk through the pipeline only visiting entities
> that participates in the stream, i.e. it follows links from sink to source
> (and not the opposite).
> 
> Which means that in a topology like this https://bit.ly/3b2MxjI
> calling v4l2_pipeline_stream_enable() from rkisp1_mainpath won't call
> .s_stream(true) for rkisp1_resizer_selfpath.
> 
> stream_count variable was added in v4l2_subdevice to handle nested calls
> to the helpers.
> This is useful when the driver allows streaming from more then one
> capture device sharing subdevices.
> 
> This patch came from the error I was facing when multistreaming from
> rkisp1 driver, where stoping one capture would call s_stream(false) in
> the pipeline, causing a stall in the second capture device.
> 
> Also, the vimc patch https://patchwork.kernel.org/patch/10948833/ won't
> be required with this patchset.
> 
> This patchset was tested on rkisp1 and vimc drivers.

I'm just curious, with this series applied can I stream simultaneously 
on multiple video devises using vimc?

> 
> Other cleanup might be possible (but I won't add in this patchset as I
> don't have the hw to test):
> 	https://git.linuxtv.org/media_tree.git/tree/drivers/media/platform/qcom/camss/camss-video.c#n430
> 	https://git.linuxtv.org/media_tree.git/tree/drivers/media/platform/omap3isp/isp.c#n697
> 	https://git.linuxtv.org/media_tree.git/tree/drivers/media/platform/stm32/stm32-dcmi.c#n680
> 	https://git.linuxtv.org/media_tree.git/tree/drivers/media/platform/xilinx/xilinx-dma.c#n97
> 
> Changes in V2:
> ====================
> The first version was calling the s_stream() callbacks from sensor to
> capture.
> 
> This was generating errors in the Scarlet Chromebook, when the sensor
> was being enabled before the ISP.
> 
> It make sense to enable subdevices from capture to sensor instead (which
> is what most drivers do already).
> 
> This v2 drops the changes from mc-entity.c, and re-implement helpers in
> v4l2-common.c
> 
> Overview of patches:
> ====================
> 
> Path 1/3 adds the helpers in v4l2-common.c, allowing nested calls by
> adding stream_count in the subdevice struct.
> 
> Patch 2/3 cleanup rkisp1 driver to use the helpers.
> 
> Patch 3/3 cleanup vimc driver to use the helpers.
> 
> Helen Koike (3):
>   media: v4l2-common: add helper functions to call s_stream() callbacks
>   media: staging: rkisp1: use v4l2_pipeline_stream_{enable,disable}
>     helpers
>   media: vimc: use v4l2_pipeline_stream_{enable,disable} helpers
> 
>  drivers/media/platform/vimc/vimc-capture.c    |  28 +++--
>  drivers/media/platform/vimc/vimc-streamer.c   |  49 +-------
>  drivers/media/v4l2-core/v4l2-common.c         | 117 ++++++++++++++++++
>  drivers/staging/media/rkisp1/rkisp1-capture.c |  76 +-----------
>  include/media/v4l2-common.h                   |  28 +++++
>  include/media/v4l2-subdev.h                   |   2 +
>  6 files changed, 173 insertions(+), 127 deletions(-)
> 
> -- 
> 2.26.0
> 

-- 
Regards,
Niklas Söderlund