Re: [PATCH v6 1/4] memory: prevent dma-reentracy issues

[Mark Cave-Ayland]

On 10/03/2023 12:45, Peter Maydell wrote:

> On Fri, 10 Mar 2023 at 12:32, Alexander Bulekov <alxndr@bu.edu> wrote:
> > This MR seems to be "lsi-ram".
> >
> >  From hw/scsi/lsi53c895a.c:
> >
> > memory_region_init_io(&s->ram_io, OBJECT(s), &lsi_ram_ops, s,
> >          "lsi-ram", 0x2000);
> >
> > So the LSI device is reading an LSI "Script" from its own IO region.. In
> > this particular case, I think there was no reason to use
> > memory_region_init_io rather than memory_region_init_ram, but this makes
> > me worried that there are other devices that use something like this.
>
> This particular device predates the entire MemoryRegion set of
> abstractions, so it might have seemed easier at the time.
> The endianness handling of the current code is also a bit
> confusing and might make it tricky to convert to a RAM MR.

Since the LSI controller is attached to a PCI BAR then the accesses from the host to 
the RAM should all be little endian (you can see the conversions in the driver I 
wrote for the 40p machine to allow it to boot Linux: 
https://github.com/openbios/openbios/blob/master/drivers/lsi.c).

I'm mildly curious that read_dword() which reads the SCRIPTS program internally 
returns the value via cpu_to_le32(), as at first glance I would expect that to be the 
other way around...



ATB,

Mark.