[PATCH] cmd: fdt: skip board specific fixup using env variable

[Wasim Khan (OSS)]

Hi Tom,

> -----Original Message-----
> From: Tom Rini <trini at konsulko.com>
> Sent: Wednesday, January 27, 2021 7:41 PM
> To: Wasim Khan (OSS) <wasim.khan at oss.nxp.com>
> Cc: sjg at chromium.org; t-kristo at ti.com; Varun Sethi <V.Sethi at nxp.com>; u-
> boot at lists.denx.de; Wasim Khan <wasim.khan at nxp.com>
> Subject: Re: [PATCH] cmd: fdt: skip board specific fixup using env variable
> 
> On Wed, Jan 27, 2021 at 02:09:48PM +0100, Wasim Khan wrote:
> 
> > From: Wasim Khan <wasim.khan at nxp.com>
> >
> > Sometimes it is useful to boot OS with already fixed-up device tree.
> > Check for env variable 'skip_board_fixup'
> > before calling ft_board_setup().
> > Current behaviour is unchanged, additionally user can set
> > skip_board_fixup to 1 to skip the fixup.
> >
> > Signed-off-by: Wasim Khan <wasim.khan at nxp.com>
> > ---
> >  common/image-fdt.c | 17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> Can you provide a specific example or two here?  Thanks!

Thank you for your comments. 

Recently I faced issue where Linux crash in PCIe was observed in customer's env.
Whereas same Linux was booting fine in my environment.  After debugging we found that U-boot was doing fixup based on SVR value. SVR check was failing in customer's env because of different SoC personality which was causing the crash in OS.
So I thought it is good idea to have an option to bypass U-boot fixup and use an already fixed-up device tree so that we can quickly check if the problem is in OS or it is caused because of missed/wrong fixup from Uboot.

Another use case I can think of is suppose if we want to introduce a new dtb fixup , we can directly add the change in a fixed-up device tree, do all experiments and once validated thoroughly , we can do the same change via Uboot fixup.