Re: [PATCH 3/3] ARM: i.mx53: Support for Voipac board. Device definition is read from Devicetree

[Rostislav Lisovy <lisovy@gmail.com>]

On Mon, 2013-11-11 at 10:54 +0100, Sascha Hauer wrote: 
> On Sat, Nov 09, 2013 at 11:14:14PM +0100, Rostislav Lisovy wrote:
> > Hello Sascha;
> > 
> > On Fri, 2013-11-08 at 09:42 +0100, Sascha Hauer wrote: 
> > > Hi Rostislav,
> > > 
> > > On Tue, Nov 05, 2013 at 03:42:07PM +0100, Rostislav Lisovy wrote:
> > > > Signed-off-by: Rostislav Lisovy <lisovy@gmail.com>
> > > > 
> > > > diff --git a/arch/arm/boards/freescale-mx53-vmx53/env/config b/arch/arm/boards/freescale-mx53-vmx53/env/config
> > > > new file mode 100644
> > > > index 0000000..3d90172
> > > > --- /dev/null
> > > > +++ b/arch/arm/boards/freescale-mx53-vmx53/env/config
> > > 
> > > Why not use defenv-2?
> > 
> > Ok; I will use it;
> > 
> > > 
> > > > diff --git a/arch/arm/boards/freescale-mx53-vmx53/flash_header.c b/arch/arm/boards/freescale-mx53-vmx53/flash_header.c
> > > > new file mode 100644
> > > > index 0000000..a6864a6
> > > > --- /dev/null
> > > > +++ b/arch/arm/boards/freescale-mx53-vmx53/flash_header.c
> > > 
> > > I'm currently generating the flash images for new boards using the
> > > imx-image tool and also generate multi board images. This is a very
> > > flexible, though maybe hard to understand mechanism. Is this the reason
> > > you haven't used it or were you not aware of it?
> > > I would rather see this board taking part in this new mechanism. Are you
> > > willing to port this over? Otherwise I could try and convert this patch,
> > > but I would depend on you testing the result.
> > 
> > I was investigating how the imx53-loco support is done, however I was
> > not sure if the 'multiboard' is the preferred way.
> > I found your patchset
> > http://www.spinics.net/lists/u-boot-v2/msg15296.html shortly describing
> > the functionality of the multiboard barebox -- I still do not understand
> > the concept. The final binary has to hold just one particular
> > 'flash_header', thus be able to boot just on one particular board.
> 
> The multi image support (I think multi image is more appropriate than
> multi board) doesn't mean that the same image is being run on multiple
> boards, it instead means that the same binary is used to generate
> multiple images. Each of these images is for a particular board. The
> advantage over the traditional mechanism is that you can have a single
> config for multiple boards. Of course this could be used to have a
> single config for completely different SoCs/Boards. This gives you
> a better compile coverage with less compilation. A more real life
> scenario might be that you have two boards which differ only in the
> amount of SDRAM. Instead of maintaining two configs for it you could
> use a single config and generate two images from it.
> 
> > I do
> > understand the flexibility of the devicetree, however something like the
> > SDRAM configuration can not be chosen 'on the fly' by the PBL?
> 
> The basic trick with the multi image support is that we compile multiple
> entry points (ENTRY_FUNCTION()). Which one is used for a particular
> image is later specified with the -e option to ld. So each image has
> one entry function specified with ENTRY_FUNCTION(). What you then do
> in this entry function is up to you. If your boards offer some
> possibility to detect the SDRAM setup then you can use it to dynamically
> detect and configure SDRAM. Then you would be able to use a single
> binary image on multiple boards with different SDRAM configuration.
> 
> On i.MX with the DCD header format the DCD is normally used to setup
> SDRAM. In this case it's not possible to have the same image for
> multiple boards. However, you could remove the SDRAM setup from DCD
> data and configure the flash header to load to the i.MX internal SRAM.
> then when in SRAM you could determine your board and setup the SDRAM
> from early code. This way a single image for multiple boards would
> be possible on i.MX aswell.
> 
> With multi image support we shift away from "compiling for a single
> board". Instead a board is simply an additional option. If this option
> makes a new image necessary, then this image will be generated along
> with images for other boards.
> My vision is that we should not have defconfigs for particular boards.
> Instead we should have defconfigs which enable a certain feature set,
> for example:
> 
> - arm_full_defconfig: All features and all boards enabled, huge binary
>   nobody uses in projects, but is useful for compile testing and
>   development
> - imx_defconfig: All i.MX boards enabled and all features necessary for
>   i.MX. More practical in real life.
> - noninteractive_defconfig: Do not prompt users, just boot.
> - $VENDOR_defconfig: supports all boards from a vendor
> - $PROJECT_defconfig: supports all boards for a particular project
>   which uses different boards or variants of boards.
> 
> I hope this makes it a bit more clearer.
> 
> Sascha
> 

Thank you for the explanation. I just resent the patch-set for the
'multi-board/multi-image' support.

Regards;
Rostislav



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