Re: [TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages

From: Simon Glass <sjg@chromium.org>
To: Julius Werner <jwerner@chromium.org>
Cc: "Manish Pandey2" <Manish.Pandey2@arm.com>,
	"François Ozog" <francois.ozog@linaro.org>,
	"Ed Stuber" <edstuber@amperecomputing.com>,
	"Boot Architecture Mailman List"
	<boot-architecture@lists.linaro.org>,
	undefined <loic.pallardy@st.com>,
	"Harb Abdulhamid OS" <abdulhamid@os.amperecomputing.com>,
	"U-Boot Mailing List" <u-boot@lists.denx.de>,
	"Arjun Khare" <akhare@amperecomputing.com>,
	"tf-a@lists.trustedfirmware.org" <tf-a@lists.trustedfirmware.org>,
	"Paul Isaac's" <paul.isaacs@linaro.org>,
	"Ron Minnich" <rminnich@google.com>,
	"Moe Ammar" <moe@amperecomputing.com>
Subject: Re: [TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages
Date: Thu, 8 Jul 2021 16:31:02 -0600	[thread overview]
Message-ID: <CAPnjgZ3PHa0DtjuaQ6XnVydCyqcA_PEbV+9btNT=KMetSsoEmg@mail.gmail.com> (raw)
In-Reply-To: <CAODwPW9fc68DkVNse304wBeYCaKi-e-0C7_53ZEusMrRTCcykg@mail.gmail.com>

Hi Julius,

On Thu, 8 Jul 2021 at 15:56, Julius Werner <jwerner@chromium.org> wrote:

> Thank you all for your feedback.
>>
>> It appears that in theory we are all happy with using bloblist with few
>> implementation details which needs to be taken care of during
>> implementation.
>>
>
> Just to clarify: are you using "bloblist" as a general term for the
> concept of a simple linked list of tagged data blobs, or to refer
> specifically to the U-Boot implementation with that name? The existing TF-A
> implementation (bl_aux_params) is basically identical in concept to the
> U-Boot bloblist, but not binary compatible. Are we talking about just
> keeping that, or throwing it away in order to reimplement the exact
> structure U-Boot is using? (I would prefer to keep the bl_aux_params as
> they are to avoid disrupting existing uses, of course. Making
> backwards-incompatible changes to an interface that passes across multiple
> repos and firmware components is always a big pain.)
>

My understanding is that it is U-Boot's bloblist, since it is the lynchpin
here, but perhaps with some changes to support features it may lack. It has
been in U-Boot for a couple of years and is supported in TPL, SPL and
U-Boot proper. It has a good set of unit tests and should be easy enough to
lift into other projects. Note that it is not really a linked list, though
that is one of the extensions proposed.

Of course every project would like not to change...

For TF-A I wonder whether it will/should in fact use devicetree if there is
a lot of complex data? TBD, I suppose.

Regards,
Simon