Re: [PATCH v1 5/6] riscv/virt: Add the PFlash CFI01 device

[Alistair Francis]

On Tue, Sep 24, 2019 at 2:32 AM Philippe Mathieu-Daudé
<address@hidden> wrote:
>
> On 9/23/19 11:46 PM, Peter Maydell wrote:
> > On Fri, 20 Sep 2019 at 23:23, Alistair Francis <address@hidden> wrote:
> >> On Thu, Sep 19, 2019 at 10:15 PM Bin Meng <address@hidden> wrote:
> >>> I don't think we should mirror what is used on ARM virt board to
> >>> create 2 flash for sifive_u. For ARM virt, there are 2 flashes because
> >>> they need distinguish secure and non-secure. For sifive_u, only one is
> >>> enough.
> >>
> >> I went back and forward about 1 or 2. Two seems more usable as maybe
> >> someone wants to include two pflash files? The Xilinx machine also has
> >> two so I'm kind of used to 2, but I'm not really fussed.
>
> The Xilinx machine has 2 because it matches the hardware.
>
> > One of the reasons for having 2 on the Arm board (we do this
> > even if we're not supporting secure vs non-secure) is that
> > then you can use one for a fixed read-only BIOS image (backed
> > by a file on the host filesystem shared between all VMs), and
> > one backed by a read-write per-VM file providing permanent
> > storage for BIOS environment variables. Notably UEFI likes to
> > work this way, but the idea applies in theory to other
> > boot loader or BIOSes I guess.
>
> IIRC Laszlo's explanation, the only reason it is that way is because the
> pflash_cfi01 model still doesn't implement sector locking. At the OVMF
> emerged from EDK2, to have a safe ROM vs DATA storage it was decided to
> use 2 different flashes.
> When I understood when this config layout started, I suggested Laszlo to
> use a real ROM to store the OVMF CODE since it is pointless to do
> firmware upgrade in virtualized environment, but he said it was too late
> to change the design.
>
> If you don't plan to run UEFI "Capsule Update" on your Virt board, I
> suggest using memory_region_init_rom() with your firmware CODE, and a
> parallel/SPI flash for the data VARStore.

We might run that one day, who knows :)

Alistair

>
> > I would suggest also checking with Markus that your code
> > for instantiating the flash devices follows the current
> > recommendations so the backing storage can be configured
> > via -blockdev. (This is a fairly recent change from June or
> > so; current-in-master virt and sbsa boards provide an example
> > of doing the right thing, I think.)
> >
> > thanks
> > -- PMM
> >