[U-Boot] [PATCH 2/2] armv8: sec_firmware: Add support for loadables in FIT

[Sumit Garg]

> -----Original Message-----
> From: York Sun
> Sent: Tuesday, October 24, 2017 8:00 PM
> To: Sumit Garg <sumit.garg at nxp.com>; u-boot at lists.denx.de
> Cc: Ruchika Gupta <ruchika.gupta at nxp.com>; Prabhakar Kushwaha
> <prabhakar.kushwaha at nxp.com>; Z.q. Hou <zhiqiang.hou at nxp.com>; Pankaj
> Gupta <pankaj.gupta at nxp.com>; Arun Pathak <arun.pathak at nxp.com>; Sahil
> Malhotra <sahil.malhotra at nxp.com>
> Subject: Re: [PATCH 2/2] armv8: sec_firmware: Add support for loadables in FIT
> 
> On 10/23/2017 09:21 PM, Sumit Garg wrote:
> <snip>
> >>
> >> Sumit,
> >>
> >> If I understand you correctly, you are parsing the secure firmware
> >> FIT image to find the loadable node and store the 64-bit load address
> >> in the scratch registers. How do you determine which scratch registers to
> use?
> >>
> >> York
> >
> > Yes your understanding is correct. The scratch registers which I used are as
> follows:
> >
> > For Chassis gen 3 platforms:
> > 	/* Assign addresses to loadable ptrs */
> > 	loadable_l = &gur->scratchrw[4];
> > 	loadable_h = &gur->scratchrw[5];
> >
> > For Chassis gen 2 platforms:
> > 	/* Assign addresses to loadable ptrs */
> > 	loadable_l = &scfg->scratchrw[2];
> > 	loadable_h = &scfg->scratchrw[3];
> >
> > I choose above scratch registers to avoid any conflict with usage of
> > scratch registers in Boot-ROM, u-boot and PPA.
> 
> I see you write to these scratch registers but never read from them.
> What's the purpose to store the address in them?
> 
> York
 
These scratch registers are used to communicate loadable address to PPA similar
to how return address is communicated in boot-location pointer registers to PPA.

PPA uses this loadable address (Trusted OS address) to initialize Trusted OS.

Sumit