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

[Sahil Malhotra (OSS)]

Hi Michael,


-----Original Message-----
From: Michael Walle <michael at walle.cc> 
Sent: Wednesday, November 17, 2021 11:51 PM
To: Sahil Malhotra (OSS) <sahil.malhotra at oss.nxp.com>
Cc: 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>; ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>
Subject: Re: [PATCH 1/2] fsl-layerscape: add dtb overlay feature

Hi Sahil,

Am 2021-11-17 19:11, schrieb Sahil Malhotra (OSS):
>> Could you please add some description what this is doing and for what 
>> this is intended? To have a "DTB overlay feature", it is enough to 
>> just enable CONFIG_OF_LIBFDT_OVERLAY.
> I will add some description, and yes for DTB overlay feature, it is 
> enough to enable CONFIG_OF_LIBFDT_OVERLAY but we need to do this step 
> before booting the kernel that's why also have to enable 
> CONFIG_OF_SYSTEM_SETUP.

> Ok. What will the overlay do? Could you give an example?
This overlay will be disabling the crypto nodes which will be used by optee in secure world, so that linux should not use it.


>> Apparently you're adding an overlay passed by optee. Doesn't this 
>> have to be applied to u-boot's control dtb too?
> Yes, we will be applying the overlay passed by optee, yes it will be 
> applied to dtb which will be passed to uboot for kernel booting.

> If I read this patch correctly, you're modifying the DT before you jump to linux. But I was asking whether you also have to modify the DT which is used by u-boot. Eg. if you disable some kind of crypto nodes (because optee will use them in secure world), this also have to communicated to u-boot, not only linux, no?
Yes, I got your point now, and is very valid, but as of now for u-boot we are just using the first available node for communicating with CAAM leaving other job rings as it is. 
So we need not to apply overlay to DTB used by uboot.

Regards,
Sahil Malhotra