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From: Jacopo Mondi <jacopo@jmondi.org>
To: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Jacopo Mondi <jacopo+renesas@jmondi.org>,
	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
Subject: Re: [PATCH v3 05/19] media: v4l2-subdev: De-deprecate init() subdev op
Date: Fri, 26 Mar 2021 12:37:05 +0100	[thread overview]
Message-ID: <20210326113705.ig3v2m5cwyrf66xb@uno.localdomain> (raw)
In-Reply-To: <20210322125144.xd4yky6jmaw56x4a@uno.localdomain>

Hi Sakari,

On Mon, Mar 22, 2021 at 01:51:44PM +0100, Jacopo Mondi wrote:
> Hi Sakari,
>
> On Sun, Mar 21, 2021 at 10:52:56PM +0200, Sakari Ailus wrote:
> > Hi Laurent and Jacopo,
> >
> > Thanks for cc'ing me.
> >
> > On Sat, Mar 20, 2021 at 05:42:12PM +0200, Laurent Pinchart wrote:
> > > Hi Jacopo,
> > >
> > > Thank you for the patch.
> > >
> > > CC'ing Sakari on v3 to get feedback.
> > >
> > > On Fri, Mar 19, 2021 at 05:41:34PM +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.
> >
> > What does the remote device's probe do that needs to be done before bus
> > config on the host side?
>
> A few lines here below:
>
>  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.
>
> >
> > Alternatively, could the remote init() work be done at the time streaming
> > is started?
>
> That would require programing the sensor, the embedded ISP at s_stream
> time which would take some time.

I'm afraid but from my testing also the chip identification is more
reliable if run in init(). As identifying chips is something that has
to happen at probe/initialization I fear it is not possible to move it
to s_stream time.

>
> I'll take this suggestion into account though and run some more tests.
>
> Thanks
>   j
>
> >
> > > >
> > > > 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.
> > > >
> > > > 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.
> > > >   *
> >
> > --
> > Kind regards,
> >
> > Sakari Ailus

  reply	other threads:[~2021-03-26 11:37 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19 16:41 [PATCH v3 00/19] media: gmsl: Reliability improvement Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 01/19] media: i2c: max9286: Adjust parameters indent Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 02/19] media: i2c: max9286: Rename reverse_channel_mv Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 03/19] media: i2c: max9286: Cache channel amplitude Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 04/19] media: i2c: max9286: Define high " Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 05/19] media: v4l2-subdev: De-deprecate init() subdev op Jacopo Mondi
2021-03-20 15:42   ` Laurent Pinchart
2021-03-21 20:52     ` Sakari Ailus
2021-03-22 12:51       ` Jacopo Mondi
2021-03-26 11:37         ` Jacopo Mondi [this message]
2021-03-19 16:41 ` [PATCH v3 06/19] media: gmsl: Reimplement initialization sequence Jacopo Mondi
2021-03-20 15:46   ` Laurent Pinchart
2021-03-19 16:41 ` [PATCH v3 07/19] media: i2c: max9286: Rework comments in .bound() Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 08/19] media: i2c: max9271: Check max9271_write() return Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 09/19] media: i2c: max9271: Introduce wake_up() function Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 10/19] media: i2c: rdamc21: Fix warning on u8 cast Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 11/19] media: i2c: rdacm21: Add dealy after OV490 reset Jacopo Mondi
2021-03-19 16:49   ` Kieran Bingham
2021-03-20 15:52     ` Laurent Pinchart
2021-03-26 11:22       ` Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 12/19] media: i2c: rdacm21: Fix OV10640 powerup Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 13/19] media: i2c: rdacm21: Power up OV10640 before OV490 Jacopo Mondi
2021-03-20 16:14   ` Laurent Pinchart
2021-03-26 11:07     ` Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 14/19] media: i2c: rdacm20: Enable noise immunity Jacopo Mondi
2021-03-20 16:16   ` Laurent Pinchart
2021-03-19 16:41 ` [PATCH v3 15/19] media: i2c: rdacm20: Embed 'serializer' field Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 16/19] media: i2c: rdacm20: Replace goto with a loop Jacopo Mondi
2021-03-20 16:17   ` Laurent Pinchart
2021-03-19 16:41 ` [PATCH v3 17/19] media: i2c: rdacm20: Report camera module name Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 18/19] media: i2c: rdacm20: Check return values Jacopo Mondi
2021-03-19 16:41 ` [PATCH v3 19/19] media: i2c: rdacm20: Re-work ov10635 reset Jacopo Mondi
2021-03-20 16:24   ` Laurent Pinchart
2021-03-26 11:11     ` Jacopo Mondi

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