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

Sahil Malhotra (OSS) sahil.malhotra at oss.nxp.com
Thu Dec 23 09:46:32 CET 2021

Hi Michael,

> -----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.

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.

Sahil Malhotra

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