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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc: kieran.bingham+renesas@ideasonboard.com,
	niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Sakari Ailus <sakari.ailus@iki.fi>
Subject: Re: [PATCH v2 16/18] media: v4l2-subdev: De-deprecate init() subdev op
Date: Mon, 15 Mar 2021 23:56:04 +0200	[thread overview]
Message-ID: <YE/X9LLrv1Hq/BL6@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20210315131512.133720-17-jacopo+renesas@jmondi.org>

Hi Jacopo,

Thank you for the patch.

On Mon, Mar 15, 2021 at 02:15:10PM +0100, Jacopo Mondi wrote:
> The init() subdev core operation is deemed to be deprecated for new
> subdevice drivers. However it could prove useful for complex
> architectures to defer operation that require access to the
> communication bus if said bus is not available (or fully configured)
> at the time when the subdevice probe() function is run.
> 
> As an example, the GMSL architecture requires the GMSL configuration
> link to be configured on the host side after the remote subdevice
> has completed its probe function. After the configuration on the host
> side has been performed, the subdevice registers can be accessed through
> the communication bus.
> 
> In particular:
> 
> 	HOST			REMOTE
> 
> 	probe()
> 	   |
> 	   ---------------------> |
> 				  probe() {
> 				     bus config()
> 				  }
> 	   |<--------------------|
> 	v4l2 async bound {
> 	    bus config()
> 	    call subdev init()
> 	   |-------------------->|
> 				 init() {
> 				     access register on the bus()
> 				}
> 	   |<-------------------
> 	}
> 
> In the GMSL use case the bus configuration requires the enablement of the
> noise immunity threshold on the remote side which ensures reliability
> of communications in electrically noisy environments. After the subdevice
> has enabled the threshold at the end of its probe() sequence the host
> side shall compensate it with an higher signal amplitude. Once this
> sequence has completed the bus can be accessed with noise protection
> enabled and all the operations that require a considerable number of
> transactions on the bus (such as the image sensor configuration
> sequence) are run in the subdevice init() operation implementation.

I think this can be considered as a reasonable use of .init(). I'd like
to get feedback from Hans and Sakari (CC'ed) though.

> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> ---
>  include/media/v4l2-subdev.h | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index d0e9a5bdb08b..3068d9940669 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -148,9 +148,18 @@ struct v4l2_subdev_io_pin_config {
>   *	each pin being configured.  This function could be called at times
>   *	other than just subdevice initialization.
>   *
> - * @init: initialize the sensor registers to some sort of reasonable default
> - *	values. Do not use for new drivers and should be removed in existing
> - *	drivers.
> + * @init: initialize the subdevice registers to some sort of reasonable default
> + *	values. Do not use for new drivers (and should be removed in existing
> + *	ones) for regular architectures where the image sensor is connected to
> + *	the host receiver. For more complex architectures where the subdevice
> + *	initialization should be deferred to the completion of the probe
> + *	sequence of some intermediate component, or the communication bus
> + *	requires configurations on the host side that depend on the completion
> + *	of the probe sequence of the remote subdevices, the usage of this
> + *	operation could be considered to allow the devices along the pipeline to
> + *	probe and register in the media graph and to defer any operation that
> + *	require actual access to the communication bus to their init() function
> + *	implementation.
>   *
>   * @load_fw: load firmware.
>   *

-- 
Regards,

Laurent Pinchart

  reply	other threads:[~2021-03-15 21:57 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15 13:14 [PATCH v2 00/18] media: gmsl: Reliability improvement Jacopo Mondi
2021-03-15 13:14 ` [PATCH v2 01/18] media: i2c: rdamc21: Fix warning on u8 cast Jacopo Mondi
2021-03-15 15:27   ` Kieran Bingham
2021-03-15 21:35   ` Laurent Pinchart
2021-03-15 13:14 ` [PATCH v2 02/18] media: i2c: rdacm20: Enable noise immunity Jacopo Mondi
2021-03-15 21:37   ` Laurent Pinchart
2021-03-16 12:56     ` Jacopo Mondi
2021-03-16 19:24       ` Laurent Pinchart
2021-03-15 13:14 ` [PATCH v2 03/18] media: i2c: rdacm20: Embedded 'serializer' field Jacopo Mondi
2021-03-15 15:29   ` Kieran Bingham
2021-03-15 13:14 ` [PATCH v2 04/18] media: i2c: rdacm20: Replace goto with a loop Jacopo Mondi
2021-03-15 15:36   ` Kieran Bingham
2021-03-15 13:14 ` [PATCH v2 05/18] media: i2c: rdacm20: Report camera module name Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 06/18] media: i2c: max9271: Check max9271_write() return Jacopo Mondi
2021-03-15 15:46   ` Kieran Bingham
2021-03-15 21:38   ` Laurent Pinchart
2021-03-15 13:15 ` [PATCH v2 07/18] media: i2c: rdacm20: Check return values Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 08/18] media: i2c: rdacm20: Re-work ov10635 reset Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 09/18] media: i2c: max9271: Introduce wake_up() function Jacopo Mondi
2021-03-15 17:14   ` Kieran Bingham
2021-03-15 21:43   ` Laurent Pinchart
2021-03-15 13:15 ` [PATCH v2 10/18] media: i2c: max9286: Adjust parameters indent Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 11/18] media: i2c: rdacm21: Fix OV10640 powerdown Jacopo Mondi
2021-03-15 17:20   ` Kieran Bingham
2021-03-15 21:45   ` Laurent Pinchart
2021-03-15 13:15 ` [PATCH v2 12/18] media: i2c: rdacm21: Give more time to OV490 to boot Jacopo Mondi
2021-03-15 17:22   ` Kieran Bingham
2021-03-17 10:04     ` Jacopo Mondi
2021-03-19  0:29       ` Laurent Pinchart
2021-03-19 14:53         ` Jacopo Mondi
2021-03-15 21:52   ` Laurent Pinchart
2021-03-15 13:15 ` [PATCH v2 13/18] media: i2c: max9286: Rename reverse_channel_mv Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 14/18] media: i2c: max9286: Cache channel amplitude Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 15/18] media: i2c: max9286: Define high " Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 16/18] media: v4l2-subdev: De-deprecate init() subdev op Jacopo Mondi
2021-03-15 21:56   ` Laurent Pinchart [this message]
2021-03-15 13:15 ` [PATCH v2 17/18] media: gmsl: Reimplement initialization sequence Jacopo Mondi
2021-03-15 13:15 ` [PATCH v2 18/18] media: i2c: max9286: Rework comments in .bound() Jacopo Mondi
2021-03-15 17:28   ` Kieran Bingham
2021-03-15 21:57   ` Laurent Pinchart

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