[PATCH][v2] powerpc/fsl-booke: Add T1040D4RDB/T1042D4RDB board support

[Priyanka Jain]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Friday, July 24, 2015 8:58 PM
> To: Jain Priyanka-B32167
> Cc: linuxppc-dev at lists.ozlabs.org
> Subject: Re: [PATCH][v2] powerpc/fsl-booke: Add T1040D4RDB/T1042D4RDB
> board support
> 
> On Wed, 2015-07-22 at 05:49 -0500, Jain Priyanka-B32167 wrote:
> >
> > > -----Original Message-----
> > > From: Wood Scott-B07421
> > > Sent: Friday, July 17, 2015 10:37 PM
> > > To: Jain Priyanka-B32167
> > > Cc: linuxppc-dev at lists.ozlabs.org
> > > Subject: Re: [PATCH][v2] powerpc/fsl-booke: Add
> > > T1040D4RDB/T1042D4RDB board support
> > >
> > > On Fri, 2015-07-17 at 01:17 -0500, Jain Priyanka-B32167 wrote:
> > > >
> > > > > -----Original Message-----
> > > > > From: Wood Scott-B07421
> > > > > Sent: Friday, July 17, 2015 1:06 AM
> > > > > To: Jain Priyanka-B32167
> > > > > Cc: linuxppc-dev at lists.ozlabs.org
> > > > > Subject: Re: [PATCH][v2] powerpc/fsl-booke: Add
> > > > > T1040D4RDB/T1042D4RDB board support
> > > > >
> > > > > > > +                i2c at 118100{
> > > > > > > +                      mux at 77{
> > > > > > > +                             compatible = "nxp,pca9546";
> > > > > > > +                             reg = <0x77>;
> > > > > > > +                             #address-cells = <1>;
> > > > > > > +                             #size-cells = <0>;
> > > > > > > +                     };
> > > > > > > +             };
> > > > > >
> > > > > > A mux with no nodes under it (and yet it has
> > > > > > #address-cells/#size- cells)?
> > > > > > What is it multiplexing?
> > > > > > [Priyanka]: PCA9546 is i2c mux device , to which other i2c
> > > > > > devices (up-to 8
> > > > > > ) can be further connected on output channels On T104xD4RDB,
> > > > > > channel 0, 1, 3 line are connected to PEX device, Channel 2 to
> > > > > > hdmi interface (initialization is done in u-boot only), other
> > > > > > channels are
> > > grounded.
> > > > > > So, as such Linux is not using the second level I2C devices
> > > > > > connected on this MUX device. So, I have not shown next level
> > > hierarchy.
> > > > > > Should I replace 'mux' with some other name? . Please suggest.
> > > > >
> > > > > The device tree describes the hardware, not just what Linux uses...
> > > > > but what I don't understand is why you describe the mux at all
> > > > > if you're not going to describe what goes underneath it.
> > > > >
> > > > [Jain Priyanka-B32167] : Is below looks OK?
> > > > i2c at 118100{
> > > >  +                      i2c at 77{
> > > >  +                             compatible = "nxp,pca9546";
> > > >  +                             reg = <0x77>;
> > > >  +                             #address-cells = <1>;
> > > >  +                             #size-cells = <0>;
> > > >  +                     };
> > > >  +             };
> > >
> > > Where in my above comment did it appear that I was complaining about
> > > the node name?
> > >
> > [Jain Priyanka-B32167]
> > From what I understand:
> > PCA9546 is a mux device and it would be good if we were able to
> > present the I2C devices on output lines as subnodes like in case of
> > B4qds board and then 'mux' name would have make more sense.
> 
> The name "mux" makes more sense regardless.
> 
> > But in case of T1040D4RDB board, output i2c lines are going to PEX
> > slots, PCI connector. I am not aware of how to represents them as sub-
> nodes in dts.
> 
> OK, so you're saying the i2c devices are pluggable (and I'm assuming by "PEX
> slots" you just mean that the physical slot is repurposed, not that the PCI
> express protocol is involved)?  Making a non-runtime-enumerable bus be
> pluggable seems like a bad idea, but if that's really what has been done,
> there needs to be a device tree that represents the entire system, not just
> the motherboard.  This could be done either via a dts file that /include/s the
> motherboard dts, or via firmware dtb edits.  The dts for the motherboard
> should include the mux node with a comment explaining what the situation
> is.
> 
[Jain Priyanka-B32167] Is the below comment looks OK?
"Output I2C data, clock lines (SDO/SC0,SD1/SC1 , SD2/SC2, SD3/SC3) are going mini PCI connector slot1, mini PCI connector slot2, HDMI connector, PEX slot respectively
 The sub-nodes will depend upon the device that will be connected on these slots"

> -Scott