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

From: Markus Armbruster
Subject: Re: [PATCH v1 5/6] riscv/virt: Add the PFlash CFI01 device
Date: Wed, 25 Sep 2019 11:00:50 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)

Alistair Francis <address@hidden> writes:

> On Mon, Sep 23, 2019 at 2:46 PM Peter Maydell <address@hidden> 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.
>> 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.
> This seems like a good reason to have two and there isn't really a
> disadvantage so I have kept it with two.


Implementing sector locking would be even better.  I'm not asking you to
do that work.

>> 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.)
> I have updated the code to more closely match the ARM virt machine, so
> I think I'm doing it correctly.

You might want to consider omitting legacy configuration options -drive
if=pflash and -bios for a simpler interface.

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