Re: [RFC PATCH 3/5] hw/pci-host/bonito: Remap PCI "lo" regions when PCIMAP reg is modified

[Peter Maydell <peter.maydell@linaro.org>]

On Fri, 1 Jan 2021 at 23:12, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> Per the datasheet (Chapter 5.7.1. "PCI address regions"),
> the PCIMAP register:
>
>   Map the 64Mbyte regions marked "PCI_Lo" in the CPU's memory map,
>   each of which can be assigned to any 64 Mbyte-aligned region of
>   PCI memory. The address appearing on the PCI bus consists of the
>   low 26 bits of the CPU physical address, with the high 6 bits
>   coming from the appropriate base6 field. Each of the three regions
>   is an independent window onto PCI memory, and can be positioned on
>   any 64Mbyte boundary in PCI space.
>
> Remap the 3 regions on reset and when PCIMAP is updated.
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  hw/pci-host/bonito.c | 49 ++++++++++++++++++++++++++++++++------------
>  1 file changed, 36 insertions(+), 13 deletions(-)
>
> diff --git a/hw/pci-host/bonito.c b/hw/pci-host/bonito.c
> index a99eced0657..c58eeaf504c 100644
> --- a/hw/pci-host/bonito.c
> +++ b/hw/pci-host/bonito.c
> @@ -137,6 +137,10 @@ FIELD(BONGENCFG, PCIQUEUE,      12, 1)
>
>  /* 4. PCI address map control */
>  #define BONITO_PCIMAP           (0x10 >> 2)      /* 0x110 */
> +FIELD(PCIMAP, LO0,               0, 6)
> +FIELD(PCIMAP, LO1,               6, 6)
> +FIELD(PCIMAP, LO2,              12, 6)
> +FIELD(PCIMAP, 2G,               18, 1)
>  #define BONITO_PCIMEMBASECFG    (0x14 >> 2)      /* 0x114 */
>  #define BONITO_PCIMAP_CFG       (0x18 >> 2)      /* 0x118 */
>
> @@ -237,6 +241,7 @@ struct BonitoState {
>      qemu_irq *pic;
>      PCIBonitoState *pci_dev;
>      MemoryRegion pci_mem;
> +    MemoryRegion pcimem_lo_alias[3];
>  };
>
>  #define TYPE_BONITO_PCI_HOST_BRIDGE "Bonito-pcihost"
> @@ -245,6 +250,31 @@ OBJECT_DECLARE_SIMPLE_TYPE(BonitoState, BONITO_PCI_HOST_BRIDGE)
>  #define TYPE_PCI_BONITO "Bonito"
>  OBJECT_DECLARE_SIMPLE_TYPE(PCIBonitoState, PCI_BONITO)
>
> +static void bonito_remap(PCIBonitoState *s)
> +{
> +    static const char *const region_name[3] = {
> +        "pci.lomem0", "pci.lomem1", "pci.lomem2"
> +    };
> +    BonitoState *bs = BONITO_PCI_HOST_BRIDGE(s->pcihost);
> +
> +    for (size_t i = 0; i < 3; i++) {
> +        uint32_t offset = extract32(s->regs[BONITO_PCIMAP], 6 * i, 6) << 26;
> +
> +        if (memory_region_is_mapped(&bs->pcimem_lo_alias[i])) {
> +            memory_region_del_subregion(get_system_memory(),
> +                                        &bs->pcimem_lo_alias[i]);
> +            object_unparent(OBJECT(&bs->pcimem_lo_alias[i]));
> +        }
> +
> +        memory_region_init_alias(&bs->pcimem_lo_alias[i], OBJECT(s),
> +                                 region_name[i], &bs->pci_mem,
> +                                 offset, 64 * MiB);
> +        memory_region_add_subregion(get_system_memory(),
> +                                    BONITO_PCILO_BASE + i * 64 * MiB,
> +                                    &bs->pcimem_lo_alias[i]);
> +    }

Rather than delete-and-reinit-and-add, it's probably better to
just create the subregions once at device startup, and then use
memory_region_set_enabled() and memory_region_set_address()
to manipulate whether the subregion is visible and what address
in the system memory it is mapped at.

thanks
-- PMM