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

[Andrew Jones <andrew.jones@linux.dev>]

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