Re: [PATCH 04/10] hw/riscv: virt: Add PCIe HIGHMEM in memmap

[Sunil V L]

On Thu, Jul 27, 2023 at 02:04:46PM +0200, Igor Mammedov wrote:
> On Thu, 27 Jul 2023 16:29:19 +0530
> Sunil V L <sunilvl@ventanamicro.com> wrote:
> 
> > On Mon, Jul 24, 2023 at 05:32:54PM +0200, Igor Mammedov wrote:
> > > On Wed, 12 Jul 2023 22:09:37 +0530
> > > Sunil V L <sunilvl@ventanamicro.com> wrote:
> > >   
> > > > PCIe High MMIO base is actually dynamic and fixed at
> > > > run time based on the RAM configured. Currently, this is
> > > > not part of the memmap and kept in separate static variable
> > > > in virt.c. However, ACPI code also needs this information
> > > > to populate DSDT. So, once the base is discovered, merge
> > > > this into the final memmap which can be used to create
> > > > ACPI tables later.  
> > > 
> > > can ACPI code fetch virt_high_pcie_memmap at runtime from
> > > host bridge (like we do in pc/q35)?
> > >   
> > Hi Igor,
> > 
> > Looking at the current design of virt machines (arm/loongarch/riscv),
> > getting this directly from the memmap looks simpler. ARM ACPI also uses
> > the memmap to get the pcie_high space. It appears to me we need some
> > more infrastructure code if ACPI needs to fetch from host bridge. I am
> > not sure why that would be beneficial.
> 
> Sure it's possible to directly hardcode access, but it becomes machine
> specific and hard to generalize/reuse (defaults might belong to machine,
> but ACPI shall pickup these from actual owner - hostbridge).
> 
> And no extra infrastructure is need, x86 manages to do that by
> using properties on host bridge (one can pre-program values on host bridge
> during it's creation, firmware can also change them later when initializing 
> PCI).
> Then DSDT generator picks up uptodate values from hostbridge
> (which is actual owner of these values) via properties.
> (basically copy pc/q35 approach). 
> 
Ahh OK. Thanks!. Let me update.

Thanks,
Sunil