Re: [Qemu-devel] [PATCH v3 2/2] hw/arm/virt-acpi-build: Add DBG2 table

[Andrew Jones <drjones@redhat.com>]

On Tue, Sep 15, 2015 at 03:44:41PM +0100, Leif Lindholm wrote:
> Add a DBG2 table, describing the pl011 UART.
> 
> Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
> ---
>  hw/arm/virt-acpi-build.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 87 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 9088248..763d531 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -351,6 +351,89 @@ build_rsdp(GArray *rsdp_table, GArray *linker, unsigned rsdt)
>      return rsdp_table;
>  }
>  
> +static int
> +dbg2_addresses_size(int num_addr)
> +{
> +    return num_addr * (sizeof(struct AcpiGenericAddress) + sizeof(uint32_t));
> +}
> +
> +static int
> +dbg2_dev_length(int num_addr, const char *namepath, int oemdata_length)
> +{
> +    int size;
> +
> +    size = sizeof(AcpiDebugPort2Device);
> +    size += dbg2_addresses_size(num_addr);
> +    size += strlen(namepath) + 1;
> +    size += oemdata_length;
> +
> +    return size;
> +}

I think macros should suffice for the above helpers.

> +
> +static void
> +build_dbg2(GArray *table_data, GArray *linker, VirtGuestInfo *guest_info)
> +{
> +    const MemMapEntry *uart_memmap = &guest_info->memmap[VIRT_UART];
> +    AcpiDebugPort2Header *dbg2;
> +    AcpiDebugPort2Device *dev;
> +    struct AcpiGenericAddress *addr;
> +    uint32_t *addr_size;
> +    char *data;
> +    const char namepath[] = ".";
> +    int address_count, oem_length, table_revision, table_size;
> +
> +    address_count = 1;
> +    oem_length = 0;
> +    table_revision = 0;
> +    table_size = sizeof(*dbg2) + dbg2_dev_length(address_count, namepath,
> +                                                 oem_length);
> +
> +    dbg2 = acpi_data_push(table_data, sizeof(*dbg2));
> +    dbg2->devices_offset = sizeof(*dbg2);
> +    dbg2->devices_count = 1;
> +
> +    dev = acpi_data_push(table_data, sizeof(*dev));
> +    dev->revision = table_revision;

dev->revision and table_revision are presumably independent. I think
they should both get their own explicit '= 0'. Doing so allows us to get
rid of the local variable. I actually find the local variables, which
are constants, a bit crufty, and would prefer to just see the numbers.

> +    dev->length = cpu_to_le16(dbg2_dev_length(address_count, namepath,
> +                                              oem_length));
> +    dev->address_count = address_count;
> +    dev->namepath_length = cpu_to_le16(strlen(namepath));

what happened to the strlen + 1

> +    dev->namepath_offset = cpu_to_le16(sizeof(*dev) +
> +                                       dbg2_addresses_size(address_count));
> +    dev->oem_data_length = cpu_to_le16(oem_length);
> +    if (oem_length) {
> +        dev->oem_data_offset = cpu_to_le16(dbg2_dev_length(address_count,
> +                                                           namepath, 0));
> +    } else {
> +        dev->oem_data_offset = 0;
> +    }

I wouldn't bother with the special oem_data handling now, since we don't
plan to use it. If somebody extends this function for nonzero oem_length
sometime, then they can deal with it.

> +    dev->port_type = cpu_to_le16(0x8000);    /* Serial */
> +    dev->port_subtype = cpu_to_le16(0x3);    /* ARM PL011 UART */
> +    dev->base_address_offset = cpu_to_le16(sizeof(*dev));
> +    dev->address_size_offset = cpu_to_le16(sizeof(*dev) +
> +                                           address_count * sizeof(*addr));

Could create another macro for this offset calculation. Actually could add
a macro for each for consistency.

> +
> +    addr = acpi_data_push(table_data, sizeof(*addr) * address_count);
> +    addr->space_id = AML_SYSTEM_MEMORY;
> +    addr->bit_width = 8;
> +    addr->bit_offset = 0;
> +    addr->access_width = 1;
> +    addr->address = cpu_to_le64(uart_memmap->base);
> +
> +    addr_size = acpi_data_push(table_data, sizeof(*addr_size) * address_count);
> +    *addr_size = cpu_to_le32(sizeof(*addr));
> +
> +    data = acpi_data_push(table_data, strlen(namepath) + 1);

After dropping the oem data handling code, then we can use a better name
than 'data' for this.

> +    strcpy(data, namepath);
> +
> +    if (oem_length) {
> +        data = acpi_data_push(table_data, oem_length);
> +    }
> +
> +    build_header(linker, table_data, (void *)dbg2, "DBG2", table_size,
> +                 table_revision);
> +}
> +
>  static void
>  build_spcr(GArray *table_data, GArray *linker, VirtGuestInfo *guest_info)
>  {
> @@ -577,7 +660,7 @@ void virt_acpi_build(VirtGuestInfo *guest_info, AcpiBuildTables *tables)
>      dsdt = tables_blob->len;
>      build_dsdt(tables_blob, tables->linker, guest_info);
>  
> -    /* FADT MADT GTDT MCFG SPCR pointed to by RSDT */
> +    /* FADT MADT GTDT MCFG DBG2 SPCR pointed to by RSDT */
>      acpi_add_table(table_offsets, tables_blob);
>      build_fadt(tables_blob, tables->linker, dsdt);
>  
> @@ -591,6 +674,9 @@ void virt_acpi_build(VirtGuestInfo *guest_info, AcpiBuildTables *tables)
>      build_mcfg(tables_blob, tables->linker, guest_info);
>  
>      acpi_add_table(table_offsets, tables_blob);
> +    build_dbg2(tables_blob, tables->linker, guest_info);
> +
> +    acpi_add_table(table_offsets, tables_blob);
>      build_spcr(tables_blob, tables->linker, guest_info);
>  
>      /* RSDT is pointed to by RSDP */
> -- 
> 2.1.4
> 
>

I liked Shannon's suggestion to use more acpi_data_pushing, which this
version provides, but, as we're making assumptions (only one device
and no OEM data), then I think we can further simplify this version.

Thanks,
drew