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

[Michael Walle <michael@walle.cc>]

Hi Sahil,

Am 2021-12-23 09:46, schrieb Sahil Malhotra (OSS):
>> -----Original Message-----
>> From: U-Boot <u-boot-bounces@lists.denx.de> On Behalf Of Michael Walle
>> Sent: Monday, December 20, 2021 6:23 PM
>> To: Sahil Malhotra (OSS) <sahil.malhotra@oss.nxp.com>
>> Cc: ZHIZHIKIN Andrey <andrey.zhizhikin@leica-geosystems.com>; Clément
>> Faure <clement.faure@nxp.com>; Gaurav Jain <gaurav.jain@nxp.com>;
>> Pankaj Gupta <pankaj.gupta@nxp.com>; Priyanka Jain
>> <priyanka.jain@nxp.com>; u-boot@lists.denx.de; Varun Sethi
>> <V.Sethi@nxp.com>; Ye Li <ye.li@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.

> 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.

-michael