[U-Boot] [PATCH v2 00/11] SiFive FU540 Support

[Anup Patel <Anup.Patel@wdc.com>]

> -----Original Message-----
> From: Atish Patra [mailto:atish.patra at wdc.com]
> Sent: Monday, January 21, 2019 7:07 AM
> To: Auer, Lukas <lukas.auer@aisec.fraunhofer.de>; sjg at chromium.org;
> bmeng.cn at gmail.com; rick at andestech.com; Anup Patel
> <Anup.Patel@wdc.com>; joe.hershberger at ni.com;
> yamada.masahiro at socionext.com
> Cc: paul.walmsley at sifive.com; palmer at sifive.com; hch at infradead.org; u-
> boot at lists.denx.de; agraf at suse.de
> Subject: Re: [PATCH v2 00/11] SiFive FU540 Support
> 
> On 1/20/19 12:34 PM, Auer, Lukas wrote:
> > Hi Anup,
> >
> > On Fri, 2019-01-18 at 11:18 +0000, Anup Patel wrote:
> >> This patchset adds SiFive Freedom Unleashed (FU540) support to RISC-V
> >> U-Boot.
> >>
> >> The patches are based upon latest RISC-V U-Boot tree
> >> (git://git.denx.de/u-boot-riscv.git) at commit id
> >> 91882c472d8c0aef4db699d3f2de55bf43d4ae4b
> >>
> >> All drivers namely: SiFive PRCI, SiFive Serial, and Cadance MACB
> >> Ethernet work fine on actual SiFive Unleashed board and QEMU sifive_u
> >> machine.
> >>
> >
> > Thanks for working on this! Are you also planning on adding the
> > features of the FSBL to U-Boot to remove it from the boot flow?
> >
> 
> That would also mean that adding M-mode capability in U-boot. As of now
> the expected boot flow is
> 
> ZSBL->FSBL------->BBL/OpenSBI--------->U-boot------------->Linux
> (M mode from ROM)  (M mode from DRAM)  (S Mode from DRAM)  (S Mode
> from
> DRAM)
> 
> This is not the mandated boot flow but running the last stage boot loader
> from S-mode gives flexibility in virtualization in future.

To elaborate more on what Atish already mentioned, our rationale behind
ZSBL->FSBL->BBL/OpenSBI->U-Boot(or Any other general bootloader) is
as follows:
1. We don't want to replicate FSBL code (DRAM and other system-level init)
in general purpose bootloaders (U-Boot, UEFI/Tianocore, etc)
2. We don't want to replicate SBI runtime implementation in general
purpose bootloaders (U-Boot, UEFI/Tianocore, etc)
3. We want to use general purpose bootloader (U-Boot, UEFI/Tianocore, etc)
inside Guest/VM (S-mode)

Of course, above boot flow is not mandatory. There could be RISC-V systems
where prior booting stages (such as ZSBL and FSBL) don't exist so users have
following options:
1. Run U-Boot in M-mode for such RISC-V systems and link to OpenSBI static
library for SBI runtime services
2. Run U-Boot in S-mode but do most system-level initialization (including
DRAM init) in OpenSBI firmware. In other words, use following booting flow:
OpenSBI (M-mode) -> U-Boot (S-mode)

For point1 above, we will first try it with U-Boot M-mode on QEMU Virt
machine.

> 
> > I was able to run U-Boot and boot Linux successfully on a SiFive
> > HiFive Unleashed board with this patch series. I had to make one more
> > change, because U-Boot was not able to find a serial driver and
> > paniced as a result.
> >
> > I fixed this by making the serial driver available pre-relocation. For
> > this, the soc compatible has to be added to cpu/generic/cpu.c and the
> > serial driver must have the DM_FLAG_PRE_RELOC flag set.
> >
> > Another way would be to add a "stdout-path" property to the chosen
> > node of the device tree.
> >
> 
> Currently, we modified the DT to add stdout-path in prior stage boot loader.
> 
> Regards,
> Atish
> > Thanks,
> > Lukas
> >
Regards,
Anup