Re: [Qemu-devel] [PATCH 4/7] m25p80: add a m25p80_set_rom_storage() routine

[mar.krzeminski]

Hi Cedric,

W dniu 23.09.2016 o 10:28, Cédric Le Goater pisze:
> On 09/23/2016 10:17 AM, Peter Maydell wrote:
> > On 23 September 2016 at 08:19, Cédric Le Goater <address@hidden> wrote:
> > > But the goal is to boot from the device, so I added a memory region alias
> > > at 0 to trigger the flash module mmios at boot time, as this is where
> > > u-boot expects to be.
> > >
> > > and I fell in this trap :/
> > >
> > >          aspeed_smc_flash_read: To 0x0 of size 1: 0xbe mode:0
> > >          Bad ram pointer (nil)
> > >          Aborted (core dumped)
> > >
> > > There is a failure in get_page_addr_code(), possibly because qemu uses
> > > byte per byte reads of the code (cpu_ldub_code). But this is beyond my
> > > understanding of qemu's internal.
> > This is a bug in how we report the problem, but the underlying
> > issue here is attempting to execute from something that's not RAM
> > or ROM. You can't execute code out of something backed by MMIO.
> OK. So I see two solutions. T
>
> The "brutal" one which is to copy the flash contents in a rom blob
> at 0, but there is still an issue in getting access to the storage
> anyhow, as it is internal to m25p80. Or we should get the name of the
> backing file of the drive but I am not sure we are expected to do
> that as I don't see any API for it.
>
> The other solution is something like this patch which lets the storage
> of the flash device be assigned externally.
Since I do not like dirty hacks in the code, I want just to suggest a 
workaround,
that probably you will not like ;]

As Qemu expects that first running code will be in ROM or RAM memory,
you can implement in your board -bios option that you will use to
pass u-boot binary to rom memory, or even use generic loader functionality
when it reach master.

Thanks,
Marcin

> Thanks,
>
> C.