[v2,3/3] hw/arm/virt_acpi_build: Generate DBG2 table

ARM SBBR specification mandates DBG2 table (Debug Port Table 2).
this latter allows to describe one or more debug ports.

Generate an DBG2 table featuring a single debug port, the PL011.

The DBG2 specification can be found at:
https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/acpi-debug-port-table?redirectedfrom=MSDN

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---
v1 -> v2:
- rebased on Igor's refactoring
---
 hw/arm/virt-acpi-build.c | 64 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

On Mon,  6 Sep 2021 14:31:39 +0200
Eric Auger <eric.auger@redhat.com> wrote:

> ARM SBBR specification  mandates DBG2 table (Debug Port Table 2).
                        ^^ revision here, and possibly a pointer [chapter]
                           to concrete place in spec where it's said.

> this latter allows to describe one or more debug ports.
> 
> Generate an DBG2 table featuring a single debug port, the PL011.
> 
> The DBG2 specification can be found at:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/acpi-debug-port-table?redirectedfrom=MSDN

links tend to go stale, I'd use a combo of name and optionally link here:
 "Microsoft Debug Port Table 2 (DBG2)"
    link
 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>

table looks correct,
so only style related thing to fix to match the common
ACPI code style.

> 
> ---
> v1 -> v2:
> - rebased on Igor's refactoring
> ---
>  hw/arm/virt-acpi-build.c | 64 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 63 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 488ea04eed7..de604e79779 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -512,6 +512,65 @@ build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>      acpi_table_composed(linker, &table);
>  }
>  
> +/* Debug Port Table 2 (DBG2) */
> +static void
> +build_dbg2(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
> +{
> +    AcpiTable table = { .sig = "DBG2", .rev = 3, .oem_id = vms->oem_id,
> +                        .oem_table_id = vms->oem_table_id };
> +    int dbg2devicelength, baseaddroffset = 22, namespace_length;
> +    char name[] = "COM0";
const?

Also I'd move here:
       const int namespace_length = sizeof(name);

> +
> +    acpi_init_table(&table, table_data);
> +
> +    namespace_length = sizeof name;
> +    dbg2devicelength = baseaddroffset +
> +                       sizeof(struct AcpiGenericAddress) + 4 + namespace_length;
                          ^^^^, fragile as it's subject to alignment which depends on target

I suggest following style:
       
       dbg2devicelength = 22 /* BaseAddressRegister[] offset, fixed size table header */ +
                          12 /* BaseAddressRegister[] */ +
                          4 /* AddressSize[] */
                          namespace_length /* NamespaceString[] */;

       and drop 'baseaddroffset' and 'sizeof(struct AcpiGenericAddress)'
       to be more consistent with other ACPI code to annotate where lengths come from

> +    /* offset to the first debug struct */
         comment should be verbatim field name from spec table, i.e. in this case 
            /* OffsetDbgDeviceInfo */
         ditto for the rest of field comments

> +    build_append_int_noprefix(table_data, 44, 4);
> +    /* number of debug device info struct entries */
> +    build_append_int_noprefix(table_data, 1, 4);
> +
> +    /* debug device info structure */

copy from spec, for ease to find it using just copy/past,

 /* Table 2. Debug Device Information structure format */

> +    /* revision */
> +    build_append_int_noprefix(table_data, 0, 1);
> +    /* length */
> +    build_append_int_noprefix(table_data, dbg2devicelength, 2);
> +    /* register count */
> +    build_append_int_noprefix(table_data, 1, 1);
> +    /* name path length */
> +    build_append_int_noprefix(table_data, namespace_length, 2);
> +    /* name path offset */
> +    build_append_int_noprefix(table_data, 38, 2);
> +    /* oem data length */
> +    build_append_int_noprefix(table_data, 0, 2);
> +    /* oem data offset (0 means no OEM data) */
> +    build_append_int_noprefix(table_data, 0, 2);
> +    /* port type (serial port) */
> +    build_append_int_noprefix(table_data, 0x8000, 2);
values could be annotated like following, using description from spec:

          build_append_int_noprefix(table_data, 0x8000 /* Serial */, 2);

> +    /* port subtype (ARM PL011)*/
> +    build_append_int_noprefix(table_data, 0x3, 2);
                                             0x3 /* ARM PL011 UART */

it gives checkpatch warning but all APCI code uses this style,
so it's fine

> +    /* reserved */
> +    build_append_int_noprefix(table_data, 0, 2);
> +    /* base address offset */
> +    build_append_int_noprefix(table_data, 22, 2);
> +    /* address size offset */
> +    build_append_int_noprefix(table_data, 34, 2);
> +
> +    /* BaseAddressRegister */
> +    build_append_gas(table_data, AML_AS_SYSTEM_MEMORY, 8, 0, 1,
> +                     vms->memmap[VIRT_UART].base);
> +
> +    /* AddressSize (PL011 UART length) */
> +    build_append_int_noprefix(table_data, 0x1000, 4);
                                             ^^^^
at least point out where it comes from or use macro to define
value and use it here and in pl011_init()


> +
> +    /* NamespaceString */
> +    g_array_append_vals(table_data, name, namespace_length);
> +
> +    acpi_table_composed(linker, &table);
> +};
> +
>  /*
>   * ACPI spec, Revision 5.1 Errata A
>   * 5.2.12 Multiple APIC Description Table (MADT)
> @@ -770,7 +829,7 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables)
>      dsdt = tables_blob->len;
>      build_dsdt(tables_blob, tables->linker, vms);
>  
> -    /* FADT MADT GTDT MCFG SPCR pointed to by RSDT */
> +    /* FADT MADT GTDT MCFG SPCR DBG2 pointed to by RSDT */
>      acpi_add_table(table_offsets, tables_blob);
>      build_fadt_rev5(tables_blob, tables->linker, vms, dsdt);
>  
> @@ -793,6 +852,9 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables)
>      acpi_add_table(table_offsets, tables_blob);
>      build_spcr(tables_blob, tables->linker, vms);
>  
> +    acpi_add_table(table_offsets, tables_blob);
> +    build_dbg2(tables_blob, tables->linker, vms);
> +
>      if (vms->ras) {
>          build_ghes_error_table(tables->hardware_errors, tables->linker);
>          acpi_add_table(table_offsets, tables_blob);