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Re: [PATCH 00/18] hw/riscv: Add Microchip PolarFire SoC Icicle Kit board

From: Anup Patel
Subject: Re: [PATCH 00/18] hw/riscv: Add Microchip PolarFire SoC Icicle Kit board support
Date: Tue, 18 Aug 2020 19:25:24 +0530

On Tue, Aug 18, 2020 at 6:39 PM <Cyril.Jean@microchip.com> wrote:
> On 8/18/20 7:17 AM, Anup Patel wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the 
> > content is safe
> >
> > On Tue, Aug 18, 2020 at 1:23 AM <Cyril.Jean@microchip.com> wrote:
> >> On 8/17/20 8:28 PM, Alistair Francis wrote:
> >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
> >>> the content is safe
> >>>
> >>> On Mon, Aug 17, 2020 at 11:12 AM via <qemu-devel@nongnu.org> wrote:
> >>>> Hi Anup,
> >>>>
> >>>> On 8/17/20 11:30 AM, Bin Meng wrote:
> >>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
> >>>>> the content is safe
> >>>>>
> >>>>> Hi Anup,
> >>>>>
> >>>>> On Sat, Aug 15, 2020 at 1:44 AM Anup Patel <anup@brainfault.org> wrote:
> >>>>>> On Fri, Aug 14, 2020 at 10:12 PM Bin Meng <bmeng.cn@gmail.com> wrote:
> >>>>>>> From: Bin Meng <bin.meng@windriver.com>
> >>>>>>>
> >>>>>>> This adds support for Microchip PolarFire SoC Icicle Kit board.
> >>>>>>> The Icicle Kit board integrates a PolarFire SoC, with one SiFive's
> >>>>>>> E51 plus four U54 cores and many on-chip peripherals and an FPGA.
> >>>>>> Nice Work !!! This is very helpful.
> >>>>> Thanks!
> >>>>>
> >>>>>> The Microchip HSS is quite convoluted. It has:
> >>>>>> 1. DDR Init
> >>>>>> 2. Boot device support
> >>>>>> 3. SBI support using OpenSBI as library
> >>>>>> 4. Simple TEE support
> >>>>>>
> >>>>>> I think point 1) and 2) above should be part of U-Boot SPL.
> >>>>>> The point 3) can be OpenSBI FW_DYNAMIC.
> >>>>>>
> >>>>>> Lastly,for point 4), we are working on a new OpenSBI feature using
> >>>>>> which we can run independent Secure OS and Non-Secure OS using
> >>>>>> U-Boot_SPL+OpenSBI (for both SiFive Unleashed and Microchip
> >>>>>> PolarFire).
> >>>>>>
> >>>>>> Do you have plans for adding U-Boot SPL support for this board ??
> >>>>> + Cyril Jean from Microchip
> >>>>>
> >>>>> I will have to leave this question to Cyril to comment.
> >>>>>
> >>>> I currently do not have a plan to support U-Boot SPL. The idea of the
> >>>> HSS is to contain all the silicon specific initialization and
> >>>> configuration code within the HSS before jumping to U-Boot S-mode. I
> >>>> would rather keep all this within the HSS for the time being. I would
> >>>> wait until we reach production silicon before attempting to move this to
> >>>> U-Boot SPL as the HSS is likely to contain some opaque silicon related
> >>>> changes for another while.
> >>> That is unfortunate, a lot of work has gone into making the boot flow
> >>> simple and easy to use.
> >>>
> >>> QEMU now includes OpenSBI by default to make it easy for users to boot
> >>> Linux. The Icicle Kit board is now the most difficult QEMU board to
> >>> boot Linux on. Not to mention it makes it hard to impossible to
> >>> support it in standard tool flows such as meta-riscv.
> >>>
> >>> Alistair
> >> If it is such a problem we can add a U-Boot SPL stage and the HSS can be
> >> treated as standard SoC ROM code.
> > It's not mandatory for U-Boot SPL to have stable DRAM calibration settings
> > from the start itself. The initial U-Boot SPL support for most
> > platforms (accross
> > architectures) usually include basic working DRAM calibration settings which
> > is later on updated with separate patches. Also, we don't need all U-Boot
> > drivers to be upstreamed in one-go as this can be done in phases.
> >
> > The advantage we have with PolarFire SoC Icicle board is that we already
> > have a U-Boot S-mode. and we believe the OpenSBI generic platform will
> > work fine for PolarFire SoC Icicle board so the only thing missing right now
> > is the U-Boot SPL support for OpenSource boot-flow.
> >
> > It will certainly accelerate open-source development if we have boot-flow
> > U-Boot_SPL => OpenSBI (FW_DYNAMIC) => U-Boot_S-mode working
> > on PolarFire SoC Icicle board. Initially, we just need DRAM, SD/eMMC,
> > and Serial port support for U-Boot SPL and U-Boot S-mode. Later on,
> > more patches can add ethernet and other booting device drivers to U-Boot.
> >
> > Regarding security services of HSS, we are working on a OpenSBI
> > feature which will allow HSS security services to run as independent
> > binary in M-mode (not linked to OpenSBI) and OpenSBI FW_DYNAMIC
> > will be a separate binary acting as a secure monitor.
> >
> > Regards,
> > Anup
> What I have in mind is that the external memory will be up and running
> by the time we get to U-Boot SPL. In the case of PolarFire SoC the ROM
> code equivalent brings up the DDR memory interface so we do not need to
> worry about this as part of U-Boot.

Keeping DRAM configuration as part of a separate ROM booting stage prior
to the U-Boot SPL sounds good to me. This will lead to following boot-flow:

ROM/HSS (M-mode) => U-Boot SPL (M-mode) => OpenSBI (M-mode) => U-Boot S-mode

> Sounds to me the component that needs to be upstreamed next is the eMMC
> support so that it can be used as part of U-Boot SPL. Correct?

Maybe as a PHASE1 patch series for PolarFire U-Boot support can
target the following:
1. Minimal U-Boot board support for PolarFire IcIcle Board with
single defconfig to build both U-Boot SPL and U-Boot S-mode
2. Serial port driver (probably re-use existing driver)
3. SD and eMMC driver

Supporting SD booting is highly desirable for PHASE1. At least,
U-Boot SPL, OpenSBI, U-Boot S-mode, and Linux should come
as separate images from SD card. The ROM/HSS can reside and
boot from on-board flash/eMMC.

Above is my suggestion based on experience with SiFive Unleashed.

The general idea behind OpenSource boot-flow is to have each
booting stage as a separate binary so that users can selectively
upgrade a particular booting stage without re-compiling/re-flashing
other booting stages.

Various distros and yocto already support building most of the above
booting stages (U-Boot, OpenSBI, Linux, etc) so we can reuse a lot
of existing work. Eventually, I am confident we will endup moving
more stuff from ROM/HSS to U-Boot SPL for ease in maintenance.


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