[PATCH 1/2] fsl-layerscape: add dtb overlay feature

[Sahil Malhotra (OSS)]

Hi Michael,

> -----Original Message-----
> From: Michael Walle <michael at walle.cc>
> Sent: Thursday, December 23, 2021 3:05 PM
> To: Sahil Malhotra (OSS) <sahil.malhotra at oss.nxp.com>
> Cc: ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>; Clément Faure
> <clement.faure at nxp.com>; Gaurav Jain <gaurav.jain at nxp.com>; Pankaj Gupta
> <pankaj.gupta at nxp.com>; Priyanka Jain <priyanka.jain at nxp.com>; u-
> boot at lists.denx.de; Varun Sethi <V.Sethi at nxp.com>; Ye Li <ye.li at nxp.com>
> Subject: Re: [EXT] Re: [PATCH 1/2] fsl-layerscape: add dtb overlay feature
> 
> Hi Sahil,
> 
> Am 2021-12-23 09:46, schrieb Sahil Malhotra (OSS):
> >> -----Original Message-----
> >> From: U-Boot <u-boot-bounces at lists.denx.de> On Behalf Of Michael
> >> Walle
> >> Sent: Monday, December 20, 2021 6:23 PM
> >> To: Sahil Malhotra (OSS) <sahil.malhotra at oss.nxp.com>
> >> Cc: ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>; Clément
> >> Faure <clement.faure at nxp.com>; Gaurav Jain <gaurav.jain at nxp.com>;
> >> Pankaj Gupta <pankaj.gupta at nxp.com>; Priyanka Jain
> >> <priyanka.jain at nxp.com>; u-boot at lists.denx.de; Varun Sethi
> >> <V.Sethi at nxp.com>; Ye Li <ye.li at nxp.com>
> >> Subject: [EXT] Re: [PATCH 1/2] fsl-layerscape: add dtb overlay
> >> feature
> >>
> >> Caution: EXT Email
> >>
> >> Hi Sahil,
> >>
> >> Am 2021-12-10 07:33, schrieb Sahil Malhotra (OSS):
> >> >> DT nodes can be statically disabled if we know that they are held
> >> >> by HAB and are not released to NS World.
> >> >>
> >> >> OP-TEE does set the status itself via dt_enable_secure_status(),
> >> >> which should present the properly configured FDT when U-Boot takes
> >> over.
> >> > Yes, OP-TEE set the status by dt_enable_secure_status() in DTB
> >> > overlay which gets merged with DTB provided for Linux bootup and
> >> > then Linux boots with merged DTB.
> >> > But u-boot uses the DTB embedded in its image. How can we modify
> >> > that DTB or merge DTB overlay passed by OP-TEE with uboot DTB ?
> >>
> >> But then u-boot has the "wrong" dtb. What is the reason, there is an
> >> overlay instead of a whole dtb? what if the overlay doesn't match the
> >> dtb?
> > "wrong" dtb means that uboot will not be aware of CAAM job ring which
> > is taken by OP-TEE and uboot on LS platforms currently use JR0, which
> > is not being used by any other entity in LS bootflow.
> 
> I don't know I follow. u-boot and linux should have the same device tree;
> regardless if that device is used or not. So applying the overlay just for linux isn't
> enough here.
Ok, I don't think that as of now, in all platforms uboot and linux have same devie
tree. 
But I will try to address your concern, but I don’t know how to apply overlay to
dtb which is embedded in u-boot binary, Can you please point me to one reference
which is doing this thing, I will take reference from there.

> > We don't use DTB in OP-TEE, but when we use CAAM in OP-TEE, OP-TEE
> > reserves One Job Ring for its use and that is communicated to Kernel
> > using DTB overlay.
> >
> >> what if the overlay doesn't match the dtb?
> > I didn't get this point, can you please elaborate a little.
> 
> You are merging a dtb fragment with an unknown dtb, right? Who says they
> match? you might have an old dtb where the supplied dtb fragment doesn't
> make any sense.
> 
> I might be missing something here. Eg. where is the linux dtb supposed to come
> from? This patchset is really missing an example and a description how things
> should work.
If supplied DTB does not match with DTB overlay fragment. then overlay will not get applied.
We don't have any control on where user picks the DTB, but we can only make sure DTB
overlay feature must work with DTBs which are upstreamed
If user makes its own customized DTB, we cannot make sure that things will work.

Regards,
Sahil Malhotra