Re: [PATCH 2/2] doc: add Arm Juno board documentation

[Andre Przywara <andre.przywara@arm.com>]

On Wed, 15 Dec 2021 12:44:16 +0000
Sudeep Holla <sudeep.holla@arm.com> wrote:

Hi Sudeep,

> On Tue, Dec 14, 2021 at 05:55:39PM +0000, Andre Przywara wrote:
> > The Juno Arm development board is an open, vendor-neutral, Armv8-A
> > development platform.
> > Add documentation that briefly outlines the hardware, and describes
> > building and installation of U-Boot.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> >  doc/board/armltd/index.rst |   1 +
> >  doc/board/armltd/juno.rst  | 117 +++++++++++++++++++++++++++++++++++++
> >  2 files changed, 118 insertions(+)
> >  create mode 100644 doc/board/armltd/juno.rst
> > 
> > diff --git a/doc/board/armltd/index.rst b/doc/board/armltd/index.rst
> > index caa6fd2bb0..68d938c647 100644
> > --- a/doc/board/armltd/index.rst
> > +++ b/doc/board/armltd/index.rst
> > @@ -8,3 +8,4 @@ ARM Ltd. boards and emulated systems
> >     :maxdepth: 2
> >  
> >     fvp64
> > +   juno
> > diff --git a/doc/board/armltd/juno.rst b/doc/board/armltd/juno.rst
> > new file mode 100644
> > index 0000000000..f37bc2c78e
> > --- /dev/null
> > +++ b/doc/board/armltd/juno.rst
> > @@ -0,0 +1,117 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +.. Copyright (C) 2021 Arm Ltd.
> > +
> > +Arm Juno board
> > +==============
> > +
> > +The `Juno development board`_ is an open, vendor-neutral, Armv8-A
> > +development platform, made by Arm Ltd. It is based on the former Versatile
> > +Express series.
> > +There are three revisions of the board:
> > +
> > +* Juno r0, with two Cortex-A57 and four Cortex-A53 cores, without PCIe.
> > +* Juno r1, with two Cortex-A57 and four Cortex-A53 cores, in later silicon
> > +  revisions, and with PCIe slots, Gigabit Ethernet and two SATA ports.
> > +* Juno r2, with two Cortex-A72 and four Cortex-A53 cores, otherwise the
> > +  same as r1.
> > +
> > +Among other things, the motherboard contains a management controller (MCP),  
> 
> IIRC the MCP is new and inside the SoC. You may refer [1], [2] and use the
> terminologies from there to be consistent with the documentation. IIRC this
> one is referred as MCC. So I would prefer s/MCP/MCC or MB throughout this
> document.

True, I managed to mix that up, thanks for pointing this out!

> > +an FPGA providing I/O interfaces (IOFPGA) and 64MB of NOR flash. The provided
> > +platform devices resemble the VExpress peripherals.
> > +The actual SoC also contains a Cortex-M3 based System Control Processor (SCP).
> > +
> > +U-Boot build
> > +------------
> > +There is only one defconfig and one binary build that covers all three board
> > +revisions, so to generate the needed ``u-boot.bin``:
> > +
> > +.. code-block:: bash
> > +
> > +    $ make vexpress_aemv8a_juno_defconfig
> > +    $ make
> > +
> > +The automatic distro boot sequence looks for UEFI boot applications and
> > +``boot.scr`` scripts on various boot media, starting with USB, then on disks
> > +connected to the two SATA ports, PXE, DHCP and eventually on the NOR flash.
> > +
> > +U-Boot installation
> > +-------------------
> > +This assumes there is some firmware on the SD card or NOR flash (see below
> > +for more details). The U-Boot binary is included in the Trusted Firmware
> > +FIP image, so after building U-Boot, this needs to be repackaged or recompiled.
> > +
> > +The NOR flash will be updated by the MCP, based on the content of a micro-SD
> > +card, which will be exported as a USB mass storage device via the rear USB-B
> > +socket. So to access that SD card, connect a USB-A->USB-B cable between some
> > +host computer and the board, and mount the FAT partition on the UMS device.
> > +If there is no device, check the upper serial port for a prompt, and
> > +explicitly enable the USB interface::
> > +
> > +    Cmd> usb_on
> > +    Enabling debug USB...
> > +  
> 
> Not sure if you need these details(above one paragraph) here if we can direct
> to one of the pages I have pointed out or specifically [3]. I guess you can
> add other topics from there and links to those subsections if you need more
> details. I am fine either way.

Yeah, I will add a link to the Juno TRM, and refer to that. But at least
on the Linux side I have seen pushback against deep links to manufacturer
websites in documentation, since those URLs tend to 404 sooner or later.
So I am tempted to keep at least that usb_on command in, since I needed to
use that at times, and it's a quick solution to a common problem.

Thanks for your comments!
Andre