dt: bindings: Add support for CSI1 bus

  From: Sakari Ailus <sakari.ailus@iki.fi>

In the vast majority of cases the bus type is known to the driver(s)
since a receiver or transmitter can only support a single one. There
are cases however where different options are possible.

Document the CSI1/CCP2 properties strobe_clk_inv and strobe_clock
properties. The former tells whether the strobe/clock signal is
inverted, while the latter signifies the clock or strobe mode.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
  

Hi Pavel,

On Wed, Dec 28, 2016 at 07:30:36PM +0100, Pavel Machek wrote:
> From: Sakari Ailus <sakari.ailus@iki.fi>
> 
> In the vast majority of cases the bus type is known to the driver(s)
> since a receiver or transmitter can only support a single one. There
> are cases however where different options are possible.
> 
> Document the CSI1/CCP2 properties strobe_clk_inv and strobe_clock
> properties. The former tells whether the strobe/clock signal is
> inverted, while the latter signifies the clock or strobe mode.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
> Signed-off-by: Pavel Machek <pavel@ucw.cz>
> 
> diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> index 9cd2a36..f0523f7 100644
> --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
> +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> @@ -76,6 +76,10 @@ Optional endpoint properties
>    mode horizontal and vertical synchronization signals are provided to the
>    slave device (data source) by the master device (data sink). In the master
>    mode the data source device is also the source of the synchronization signals.
> +- bus-type: data bus type. Possible values are:
> +  0 - CSI2
> +  1 - parallel / Bt656
> +  2 - CCP2

I wonder if we should make a difference between CCP2 and CSI-1 here, as it
may make a difference in hardware configuration. The next patch does
recognise that difference, so it should be present here as well.

Perhaps 2 - CSI1; 3 - CCP2. What do you think?

>  - bus-width: number of data lines actively used, valid for the parallel busses.
>  - data-shift: on the parallel data busses, if bus-width is used to specify the
>    number of data lines, data-shift can be used to specify which data lines are
> @@ -110,9 +114,10 @@ Optional endpoint properties
>    lane and followed by the data lanes in the same order as in data-lanes.
>    Valid values are 0 (normal) and 1 (inverted). The length of the array
>    should be the combined length of data-lanes and clock-lanes properties.
> -  If the lane-polarities property is omitted, the value must be interpreted
> -  as 0 (normal). This property is valid for serial busses only.
> -
> +- clock-inv: Clock or strobe signal inversion.
> +  Possible values: 0 -- not inverted; 1 -- inverted
> +- strobe: Whether the clock signal is used as clock or strobe. Used
> +  with CCP2, for instance.
>  
>  Example
>  -------
> 
>
  

On Wed, Dec 28, 2016 at 07:30:36PM +0100, Pavel Machek wrote:
> From: Sakari Ailus <sakari.ailus@iki.fi>
> 
> In the vast majority of cases the bus type is known to the driver(s)
> since a receiver or transmitter can only support a single one. There
> are cases however where different options are possible.

What cases specifically?

> Document the CSI1/CCP2 properties strobe_clk_inv and strobe_clock
> properties. The former tells whether the strobe/clock signal is
> inverted, while the latter signifies the clock or strobe mode.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
> Signed-off-by: Pavel Machek <pavel@ucw.cz>
> 
> diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> index 9cd2a36..f0523f7 100644
> --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
> +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> @@ -76,6 +76,10 @@ Optional endpoint properties
>    mode horizontal and vertical synchronization signals are provided to the
>    slave device (data source) by the master device (data sink). In the master
>    mode the data source device is also the source of the synchronization signals.
> +- bus-type: data bus type. Possible values are:
> +  0 - CSI2

As in MIPI CSI2?

> +  1 - parallel / Bt656
> +  2 - CCP2
>  - bus-width: number of data lines actively used, valid for the parallel busses.
>  - data-shift: on the parallel data busses, if bus-width is used to specify the
>    number of data lines, data-shift can be used to specify which data lines are
> @@ -110,9 +114,10 @@ Optional endpoint properties
>    lane and followed by the data lanes in the same order as in data-lanes.
>    Valid values are 0 (normal) and 1 (inverted). The length of the array
>    should be the combined length of data-lanes and clock-lanes properties.
> -  If the lane-polarities property is omitted, the value must be interpreted
> -  as 0 (normal). This property is valid for serial busses only.

Why is this removed?

> -
> +- clock-inv: Clock or strobe signal inversion.
> +  Possible values: 0 -- not inverted; 1 -- inverted

"invert" assumes I know what is normal and I do not. Define what is 
"normal" and name the property the opposite of that. If normal is data 
shifted on clock rising edge, then call the the property 
"clock-shift-falling-edge" for example..

> +- strobe: Whether the clock signal is used as clock or strobe. Used
> +  with CCP2, for instance.
>  
>  Example
>  -------
> 
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
  

Hi Rob,

Thanks for the review.

On Tue, Jan 03, 2017 at 02:38:54PM -0600, Rob Herring wrote:
> On Wed, Dec 28, 2016 at 07:30:36PM +0100, Pavel Machek wrote:
> > From: Sakari Ailus <sakari.ailus@iki.fi>
> > 
> > In the vast majority of cases the bus type is known to the driver(s)
> > since a receiver or transmitter can only support a single one. There
> > are cases however where different options are possible.
> 
> What cases specifically?

The existing V4L2 OF support tries to figure out the bus type and parse the
bus parameters based on that. This does not scale too well as there are
multiple serial busses that share common properties.

Some hardware also supports multiple types of busses on the same interfaces.

> 
> > Document the CSI1/CCP2 properties strobe_clk_inv and strobe_clock
> > properties. The former tells whether the strobe/clock signal is
> > inverted, while the latter signifies the clock or strobe mode.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> > Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
> > Signed-off-by: Pavel Machek <pavel@ucw.cz>
> > 
> > diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > index 9cd2a36..f0523f7 100644
> > --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
> > +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > @@ -76,6 +76,10 @@ Optional endpoint properties
> >    mode horizontal and vertical synchronization signals are provided to the
> >    slave device (data source) by the master device (data sink). In the master
> >    mode the data source device is also the source of the synchronization signals.
> > +- bus-type: data bus type. Possible values are:
> > +  0 - CSI2
> 
> As in MIPI CSI2?

Yeah, I guess it'd make sense to make this explicit.

> 
> > +  1 - parallel / Bt656
> > +  2 - CCP2
> >  - bus-width: number of data lines actively used, valid for the parallel busses.
> >  - data-shift: on the parallel data busses, if bus-width is used to specify the
> >    number of data lines, data-shift can be used to specify which data lines are
> > @@ -110,9 +114,10 @@ Optional endpoint properties
> >    lane and followed by the data lanes in the same order as in data-lanes.
> >    Valid values are 0 (normal) and 1 (inverted). The length of the array
> >    should be the combined length of data-lanes and clock-lanes properties.
> > -  If the lane-polarities property is omitted, the value must be interpreted
> > -  as 0 (normal). This property is valid for serial busses only.
> 
> Why is this removed?

Must have been by mistake. :-)

> 
> > -
> > +- clock-inv: Clock or strobe signal inversion.
> > +  Possible values: 0 -- not inverted; 1 -- inverted
> 
> "invert" assumes I know what is normal and I do not. Define what is 
> "normal" and name the property the opposite of that. If normal is data 
> shifted on clock rising edge, then call the the property 
> "clock-shift-falling-edge" for example..

The hardware documentation says this is the "strobe/clock inversion control
signal". I'm not entirely sure whether this is just signal polarity (it's a
differential signal) or inversion of an internal signal of the CCP2 block.

It might make sense to make this a private property for the OMAP 3 ISP
instead. If it's seen elsewhere, then think about it again. I doubt it
would, as CCP2 is an old bus that's used on Nokia N9, N950 and N900.

As strobe is included, I'd add that to the name. Say, "ti,clock-strobe-inv".

> 
> > +- strobe: Whether the clock signal is used as clock or strobe. Used
> > +  with CCP2, for instance.
> >  
> >  Example
> >  -------
> > 
> >
  

On Mon 2017-01-02 09:00:10, Sakari Ailus wrote:
> Hi Pavel,
> 
> On Wed, Dec 28, 2016 at 07:30:36PM +0100, Pavel Machek wrote:
> > From: Sakari Ailus <sakari.ailus@iki.fi>
> > 
> > In the vast majority of cases the bus type is known to the driver(s)
> > since a receiver or transmitter can only support a single one. There
> > are cases however where different options are possible.
> > 
> > Document the CSI1/CCP2 properties strobe_clk_inv and strobe_clock
> > properties. The former tells whether the strobe/clock signal is
> > inverted, while the latter signifies the clock or strobe mode.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> > Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
> > Signed-off-by: Pavel Machek <pavel@ucw.cz>
> > 
> > diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > index 9cd2a36..f0523f7 100644
> > --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
> > +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > @@ -76,6 +76,10 @@ Optional endpoint properties
> >    mode horizontal and vertical synchronization signals are provided to the
> >    slave device (data source) by the master device (data sink). In the master
> >    mode the data source device is also the source of the synchronization signals.
> > +- bus-type: data bus type. Possible values are:
> > +  0 - CSI2
> > +  1 - parallel / Bt656
> > +  2 - CCP2
> 
> I wonder if we should make a difference between CCP2 and CSI-1 here, as it
> may make a difference in hardware configuration. The next patch does
> recognise that difference, so it should be present here as well.
> 
> Perhaps 2 - CSI1; 3 - CCP2. What do you think?

Me, think..? Nah. :-).

Well, you have way more experience here, and yes, based on future
patches, this makes sense.

Thanks,								Pavel
  

Hi!

> Thanks for the review.
> 
> On Tue, Jan 03, 2017 at 02:38:54PM -0600, Rob Herring wrote:
> > On Wed, Dec 28, 2016 at 07:30:36PM +0100, Pavel Machek wrote:
> > > From: Sakari Ailus <sakari.ailus@iki.fi>
> > > 
> > > In the vast majority of cases the bus type is known to the driver(s)
> > > since a receiver or transmitter can only support a single one. There
> > > are cases however where different options are possible.
> > 
> > What cases specifically?
> 
> The existing V4L2 OF support tries to figure out the bus type and parse the
> bus parameters based on that. This does not scale too well as there are
> multiple serial busses that share common properties.
> 
> Some hardware also supports multiple types of busses on the same interfaces.

Ok, I'll include that in the changelog.

> > As in MIPI CSI2?
> 
> Yeah, I guess it'd make sense to make this explicit.

Ok.

> > >    should be the combined length of data-lanes and clock-lanes properties.
> > > -  If the lane-polarities property is omitted, the value must be interpreted
> > > -  as 0 (normal). This property is valid for serial busses only.
> > 
> > Why is this removed?
> 
> Must have been by mistake. :-)

Fixed.

> > > -
> > > +- clock-inv: Clock or strobe signal inversion.
> > > +  Possible values: 0 -- not inverted; 1 -- inverted
> > 
> > "invert" assumes I know what is normal and I do not. Define what is 
> > "normal" and name the property the opposite of that. If normal is data 
> > shifted on clock rising edge, then call the the property 
> > "clock-shift-falling-edge" for example..
> 
> The hardware documentation says this is the "strobe/clock inversion control
> signal". I'm not entirely sure whether this is just signal polarity (it's a
> differential signal) or inversion of an internal signal of the CCP2 block.
> 
> It might make sense to make this a private property for the OMAP 3 ISP
> instead. If it's seen elsewhere, then think about it again. I doubt it
> would, as CCP2 is an old bus that's used on Nokia N9, N950 and N900.
> 
> As strobe is included, I'd add that to the name. Say,
> "ti,clock-strobe-inv".

Hmm. N900 does not use inversion. Would it make sense to simply
hardcode it to "not-inverted" for now?

Device tree changes are PITA :-(.
									Pavel
  

Hi Pavel,

On Wed, Jan 11, 2017 at 11:06:48PM +0100, Pavel Machek wrote:
> > > > +- clock-inv: Clock or strobe signal inversion.
> > > > +  Possible values: 0 -- not inverted; 1 -- inverted
> > > 
> > > "invert" assumes I know what is normal and I do not. Define what is 
> > > "normal" and name the property the opposite of that. If normal is data 
> > > shifted on clock rising edge, then call the the property 
> > > "clock-shift-falling-edge" for example..
> > 
> > The hardware documentation says this is the "strobe/clock inversion control
> > signal". I'm not entirely sure whether this is just signal polarity (it's a
> > differential signal) or inversion of an internal signal of the CCP2 block.
> > 
> > It might make sense to make this a private property for the OMAP 3 ISP
> > instead. If it's seen elsewhere, then think about it again. I doubt it
> > would, as CCP2 is an old bus that's used on Nokia N9, N950 and N900.
> > 
> > As strobe is included, I'd add that to the name. Say,
> > "ti,clock-strobe-inv".
> 
> Hmm. N900 does not use inversion. Would it make sense to simply
> hardcode it to "not-inverted" for now?
> 
> Device tree changes are PITA :-(.

I can't remember what's used for the N9 secondary camera. As you said, we
can always add it if needed though. So works for me.