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

[York Sun]

On 10/24/2017 09:00 PM, Sumit Garg wrote:
>> -----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.

OK. So these registers are actually consumed by PPA image. That makes
more sense.

York