[U-Boot] Support of device-tree for PowerPC platform: Query

[Prabhakar Kushwaha]

Hi Simon,

> -----Original Message-----
> From: Prabhakar Kushwaha
> Sent: Thursday, June 28, 2018 11:17 AM
> To: Simon Glass <sjg at chromium.org>; York Sun <york.sun at nxp.com>
> Cc: u-boot at lists.denx.de; Poonam Aggrwal <poonam.aggrwal at nxp.com>;
> Jagdish Gediya <jagdish.gediya at nxp.com>
> Subject: RE: Support of device-tree for PowerPC platform: Query
> 
> Hi Simon,
> 
> 
> > -----Original Message-----
> > From: sjg at google.com [mailto:sjg at google.com] On Behalf Of Simon Glass
> > Sent: Thursday, June 28, 2018 3:36 AM
> > To: York Sun <york.sun at nxp.com>
> > Cc: Prabhakar Kushwaha <prabhakar.kushwaha at nxp.com>; u-
> > boot at lists.denx.de; Poonam Aggrwal <poonam.aggrwal at nxp.com>;
> Jagdish
> > Gediya <jagdish.gediya at nxp.com>
> > Subject: Re: Support of device-tree for PowerPC platform: Query
> >
> > Hi,
> >
> > On 27 June 2018 at 08:06, York Sun <york.sun at nxp.com> wrote:
> > >
> > > +Simon
> > >
> > > On 06/27/2018 01:05 AM, Prabhakar Kushwaha wrote:
> > > > Hi All,
> > > >
> > > > We are trying to add support of device-tree for PowerPC platforms.
> > > > As
> > per our analysis following 2 options can be used.
> > > >
> > > > a) CONFIG_OF_SEPARATE
> > > > b) CONFIG_OF_EMBED
> > > >
> > > > In PowerPC platforms, reset_vector is always expected at the
> > > > **last**
> > address of flash.
> > > > U-boot binary has reset_vector at last followed by __bss
> > > > sections(not
> > present in binary) and must be programmed in such a way that
> > reset_vecrot lie at **last** address of flash.
> > > >
> > > > Hence dtb cannot be appended at last of  u-boot binary.
> > > >
> > > > So there looks to be following 2 possible solutions
> > > > a) Use CONFIG_OF_SEPARATE and append dtb at start of u-boot
> binary.
> > This require change in flash map because u-boot start address needs to
> > shifted (due to reset_vector requirements).
> > > >      Exiting offset of env and fman ucode also needs shifting.
> > > > This approach
> > requires modification in almost all existing PowerPC platform to
> > adhere to new **modified** flash map.
> > > >
> > > > b) Use CONFIG_OF_EMBED and embed dtb inside u-boot. This way no
> > change in exiting flash map. But its usage is being discouraged as per
> > doc/README.fdt-control.
> > > >
> > >
> > > Clearly putting dtb at the very end doesn't work, neither last 4KB.
> > > I think we either use CONFIG_OF_EMBED (many boards use this way), or
> > > try "fdtcontroladdr".
> >
> >
> > I discourage CONFIG_OF_EMBED - it is a debug feature. I'm not sure if
> > you have other options though.
> >
> > Can the DT perhaps go before U-Boot in the flash? We would need a way
> > to find it though.
> >
> 
> Thanks for the direction.
> 
> We will be following approach "a" with updated flash map.
> We will allocate 1MB for uboot in flash. Out which 64K for DTB and 960KB for
> u-boot for future increase.
> 
> We will also update location of env and fman ucode for NXP platforms.
> 


Other thought,
 use CONFIG_OF_SEPARATE but **don’t** concatenate dtb with u-boot. In this case user has to program u-boot and dtb separately at different location. It will also have minimal impact on PowerPC platforms 

Just wondering if this approach has any disadvantages in longer run.  
What if user forget to program dtb and restart system??

--pk