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

[Wasim Khan (OSS)]

Hi Tom,

> -----Original Message-----
> From: U-Boot <u-boot-bounces at lists.denx.de> On Behalf Of Tom Rini
> Sent: Saturday, January 30, 2021 12:53 AM
> 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
> Subject: Re: [PATCH] cmd: fdt: skip board specific fixup using env variable
> 
> On Thu, Jan 28, 2021 at 08:15:33AM +0000, Wasim Khan (OSS) wrote:
> > 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.
> 
> OK, I can see how this can be useful in some circumstances, thanks.
> What I'd like to see is updating checkpatch.pl to have a check that we aren't
> setting this by default in environments (something like the check that exists now
> for (fdt|initrd)_high=0xffffffff should be a good
> reference) as my worry is that someone will decide that's how to work-around
> some issue and we'll end up in another nightmare down the road of
> uncorrected dtbs causing other problems.  Thanks!
> 
> --
> Tom

Thanks, If I understood your comment correctly, you suggesting to add 'skip_board_fixup' to CONFIG_EXTRA_ENV_SETTINGS for all of our platforms and check its default value in checkpatch.pl , which must be 0 ?