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Re: [Qemu-ppc] [PATCH 15/15] ppc: Add aCube Sam460ex board


From: BALATON Zoltan
Subject: Re: [Qemu-ppc] [PATCH 15/15] ppc: Add aCube Sam460ex board
Date: Thu, 24 Aug 2017 23:37:09 +0200 (CEST)
User-agent: Alpine 2.21 (BSF 202 2017-01-01)

On Thu, 24 Aug 2017, David Gibson wrote:
On Wed, Aug 23, 2017 at 01:12:06PM +0200, BALATON Zoltan wrote:
On Wed, 23 Aug 2017, David Gibson wrote:
On Sun, Aug 20, 2017 at 07:23:05PM +0200, BALATON Zoltan wrote:
Add emulation of aCube Sam460ex board based on AMCC 460EX embedded SoC.
This is not a full implementation yet with a lot of components still
missing but enough to start a Linux kernel and the U-Boot firmware.

Signed-off-by: Fran├žois Revol <address@hidden>
Signed-off-by: BALATON Zoltan <address@hidden>

As usual, only fairly superficial review here.

---
 default-configs/ppcemb-softmmu.mak |   3 +
 hw/ppc/Makefile.objs               |   2 +
 hw/ppc/sam460ex.c                  | 611 +++++++++++++++++++++++++++++++++++++
 3 files changed, 616 insertions(+)
 create mode 100644 hw/ppc/sam460ex.c

diff --git a/default-configs/ppcemb-softmmu.mak 
b/default-configs/ppcemb-softmmu.mak
index 635923a..90b42f0 100644
--- a/default-configs/ppcemb-softmmu.mak
+++ b/default-configs/ppcemb-softmmu.mak
[...]
+/*****************************************************************************/
+/* SPD eeprom content from mips_malta.c */

What's the connection with mips_malta?

The board's firmware wants to see SPD EEPROMs of the connected memory while
initialising the memory controller. This is why we need to implement SDRAM
controller, I2C and SPD EEPROMs. MIPS malta board had already SPD EEPROM
implementation so this is based on that. The comment just indicates where
this code comes from.

Ok.

[snip]
+        env->nip = bi->entry;
+
+        /* Create a mapping for the kernel.  */
+        mmubooke_create_initial_mapping(env, 0, 0);
+        env->gpr[6] = tswap32(EPAPR_MAGIC);

I'm pretty sure the tswap can't be right here.  env->gpr is in host
native order and I'd expect the constant to be as well.

I know nothing about this, maybe Francois remembers why it's there. But
booting linux with -kernel works so it's probably either correct or does not
matter.

Have you attempted it on both BE and LE hosts though?

No, I don't have a BE host, only tried on LE. I'm guessing this may come from hw/ppc/virtex_ml507.c where EPAPR_MAGIC is also swapped. The only other place this magic number appears is in e500 where it's not swapped though so I don't really know what should be correct here. In u-boot sources (arch/powerpc/lib/bootm.c) it seems to use this magic if CONFIG_OF_LIBFDT is defined which seems to be set for this board so that means we likely need this (but maybe not for the legacy uImages I've tried). Since CPU is big endian and constant is defined on the host this probably should be cpu_to_be32(EPAPR_MAGIC). Does that sound better?

[...]
+    /* FIXME: remove this after fixing l2sram mapping in ppc440_uc.c? */
+    memory_region_init_ram(l2cache_ram, NULL, "ppc440.l2cache_ram", 256 << 10,
+                           &error_abort);
+    memory_region_add_subregion(address_space_mem, 0x400000000LL, l2cache_ram);
+
+    /* USB */
+    sysbus_create_simple(TYPE_PPC4xx_EHCI, 0x4bffd0400, uic[2][29]);
+    dev = qdev_create(NULL, "sysbus-ohci");
+    qdev_prop_set_string(dev, "masterbus", "usb-bus.0");
+    qdev_prop_set_uint32(dev, "num-ports", 6);
+    qdev_init_nofail(dev);
+    sbdev = SYS_BUS_DEVICE(dev);
+    sysbus_mmio_map(sbdev, 0, 0x4bffd0000);
+    sysbus_connect_irq(sbdev, 0, uic[2][30]);
+    usb_create_simple(usb_bus_find(-1), "usb-kbd");
+    usb_create_simple(usb_bus_find(-1), "usb-mouse");
+
+    /* PCI bus */
+    ppc460ex_pcie_init(env);
+    /*XXX: FIXME: is this correct? */
+    dev = sysbus_create_varargs("ppc440-pcix-host", 0xc0ec00000,
+                                uic[1][0], uic[1][20], uic[1][21], uic[1][22],
+                                NULL);
+    pci_bus = (PCIBus *)qdev_get_child_bus(dev, "pci.0");
+    if (!pci_bus) {
+        fprintf(stderr, "couldn't create PCI controller!\n");
+        exit(1);
+    }
+    memory_region_init_alias(isa, NULL, "isa_mmio", get_system_io(),
+                             0, 0x10000);
+    memory_region_add_subregion(get_system_memory(), 0xc08000000, isa);

Does it really make sense to just embed the ISA IO space here, rather
than actually instanting a PCI<->ISA bridge?

I'm not sure if this is correct but I don't know how it's handled on real
hardware. The board does not have ISA and I don't think it has a bridge but
the IO space appears at this location according to the datasheet (In System
Memory Address Map it's listed as PCI I/O 0xc08000000-0xc0800ffff) and
clients expect PCI card's io registers to be accessible here. If anyone
knows how it's done on real hardware and if there's a better way to model
this please let me know.

Ah, ok.  I think the confusion here is that you can have PCI I/O space
without ISA or a system IO space.  In fact that's pretty standard on
things without a CPU level IO space (which means just about everything
except x86).

But in that case I'd expect the PCI host bridge to map its IO memory
regions directly into address_space_memory rather than involving the
global address_space_io (what get_system_io()) returns.  The only
reason I can see that you'd need to involve get_system_io() is if you
have devices registering themselves directly into the global IO space,
which should only happen for legacy ISA devices, which it sounds like
you don't have.

Possibly this is an error in the PCI bridge implementation that your
code here is essentially a workaround for, though.

So in my understanding, there's a system_io space created automatically which appears in the memory tree anyway but would otherwise be unused and this was just reused here for the pci io space so it does not need another memory region for this. If it's not acceptable this way (although ppc440_bamboo.c and ppc4xx_pci.c also does it the exact same way) an alternative may be to change it to add another mem region for io to ppc440_pcix.c (although it already has iomem for pci.reg so this might be more confusing than using system_io here) but I think pcix device can't map this to address_space_memory itself because this device could appear in different SoCs where the memory areas might be at different addresses so this new region should then be registered as a sysbus mmio space and be mapped from the board code with sysbus_mmio_map()? I find that much more confusing than how it's done now which is also more consistent with existing code modelling similar devices.

+    /* PCI devices */
+    pci_create_simple(pci_bus, PCI_DEVFN(6, 0), "sm501");
+    /* SoC has a single SATA port but we don't emulate that yet
+     * However, firmware and usual clients have driver for SiI311x
+     * so add one for convenience by default */
+    pci_create_simple(pci_bus, -1, "sii3112");

You should probably not create this when started with -nodefaults.

We don't emulate the on-board SATA port of the SoC and without this there's
no other way to connect disks (maybe over USB, but firmware has a bug which
prevents that too even on real hardware AFAIK, I've backported a fix which
made booting from USB work but that broke keyboard) so while this is an
external card it's pretty much unusable without this so it's added by
default.

Yes, but you're not just adding it by default, you're adding it
*always*.  -nodefaults should turn that off (and the user will need to
manually instantiate it - or another disk controller, I guess).

OK I got it now. I still don't see when -nodefaults could be useful to cripple the board and make it easier to create non-working configurations but I can easily add this conditional around this line and hope users stay away from this switch and won't complain when it does not boot when they use it. (Well, it does not really boot most of the time without this switch either so I don't think it matters much at the moment :-) )
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