Re: [kvm-unit-tests PATCH v3 04/27] lib: Add support for the XSDT ACPI table

Andrew Jones
2022-07-01T09:49:55Z

On Thu, Jun 30, 2022 at 11:03:01AM +0100, Nikos Nikoleris wrote:
> XSDT provides pointers to other ACPI tables much like RSDT. However,
> contrary to RSDT that provides 32-bit addresses, XSDT provides 64-bit
> pointers. ACPI requires that if XSDT is valid then it takes precedence
> over RSDT.
>
> Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
> ---
> lib/acpi.h | 6 ++++++
> lib/acpi.c | 37 +++++++++++++++++++++++++++++++------
> 2 files changed, 37 insertions(+), 6 deletions(-)
>
> diff --git a/lib/acpi.h b/lib/acpi.h
> index b853a55..c5f0aa5 100644
> --- a/lib/acpi.h
> +++ b/lib/acpi.h
> @@ -14,6 +14,7 @@
>
> #define RSDP_SIGNATURE ACPI_SIGNATURE('R','S','D','P')
> #define RSDT_SIGNATURE ACPI_SIGNATURE('R','S','D','T')
> +#define XSDT_SIGNATURE ACPI_SIGNATURE('X','S','D','T')
> #define FACP_SIGNATURE ACPI_SIGNATURE('F','A','C','P')
> #define FACS_SIGNATURE ACPI_SIGNATURE('F','A','C','S')
>
> @@ -57,6 +58,11 @@ struct rsdt_descriptor_rev1 {
> u32 table_offset_entry[1];
> };
>
> +struct acpi_table_xsdt {
> + ACPI_TABLE_HEADER_DEF
> + u64 table_offset_entry[1];
> +};
> +
> struct fadt_descriptor_rev1
> {
> ACPI_TABLE_HEADER_DEF /* ACPI common table header */
> diff --git a/lib/acpi.c b/lib/acpi.c
> index b7fd923..240a922 100644
> --- a/lib/acpi.c
> +++ b/lib/acpi.c
> @@ -40,6 +40,7 @@ void *find_acpi_table_addr(u32 sig)
> {
> struct rsdp_descriptor *rsdp;
> struct rsdt_descriptor_rev1 *rsdt;
> + struct acpi_table_xsdt *xsdt = NULL;
> void *end;
> int i;
>
> @@ -64,17 +65,41 @@ void *find_acpi_table_addr(u32 sig)
>
> rsdt = (void *)(ulong)rsdp->rsdt_physical_address;
> if (!rsdt || rsdt->signature != RSDT_SIGNATURE)
> - return NULL;
> + rsdt = NULL;

Now that we set rsdt to NULL in the body of this if, the
condition may look a bit better as

(rsdt && rsdt->signature != RSDT_SIGNATURE)

>
> if (sig == RSDT_SIGNATURE)
> return rsdt;
>
> - end = (void *)rsdt + rsdt->length;
> - for (i = 0; (void *)&rsdt->table_offset_entry[i] < end; i++) {
> - struct acpi_table *t = (void *)(ulong)rsdt->table_offset_entry[i];
> - if (t && t->signature == sig) {
> - return t;
> + /*
> + * When the system implements APCI 2.0 and above and XSDT is
> + * valid we have use XSDT to find other ACPI tables,
^ to

> + * otherwise, we use RSDT.
> + */
> + if (rsdp->revision == 2)
> + xsdt = (void *)(ulong)rsdp->xsdt_physical_address;

The (ulong) cast shouldn't be necessary

maybe add a blank line here

> + if (!xsdt || xsdt->signature != XSDT_SIGNATURE)

Same comment as above

> + xsdt = NULL;
> +
> + if (sig == XSDT_SIGNATURE)
> + return xsdt;
> +
> + if (xsdt) {
> + end = (void *)(ulong)xsdt + xsdt->length;

The (ulong) cast shouldn't be necessary.

> + for (i = 0; (void *)&xsdt->table_offset_entry[i] < end; i++) {
> + struct acpi_table *t = (void *)xsdt->table_offset_entry[i];
> +
> + if (t && t->signature == sig)
> + return t;
> + }
> + } else if (rsdt) {
> + end = (void *)rsdt + rsdt->length;
> + for (i = 0; (void *)&rsdt->table_offset_entry[i] < end; i++) {
> + struct acpi_table *t = (void *)(ulong)rsdt->table_offset_entry[i];
> +
> + if (t && t->signature == sig)
> + return t;
> }
> }
> +
> return NULL;
> }
> --
> 2.25.1
>

Besides the nits

Reviewed-by: Andrew Jones <andrew.jones@linux.dev>

Thanks,
drew