Subject: [PATCH 1/5] acpi: Add basic device probing infrastructure

From: [email-masked] (Lorenzo Pieralisi)
Date: Mon, 7 Sep 2015 17:00:45 +0100

[+M.Salter]

On Fri, Sep 04, 2015 at 06:06:48PM +0100, Marc Zyngier wrote:
> IRQ controllers and timers are the two types of device the kernel
> requires before being able to use the device driver model.
> 
> ACPI so far lacks a proper probing infrastructure similar to the one
> we have with DT, where we're able to declare IRQ chips and
> clocksources inside the driver code, and let the core code pick it up
> and call us back on a match. This leads to all kind of really ugly
> hacks all over the arm64 code and even in the ACPI layer.
> 
> In order to allow some basic probing based on the ACPI tables,
> introduce "struct acpi_probe_entry" which contains just enough
> data and callbacks to match a table, an optional subtable, and
> call a probe function. A driver can, at build time, register itself
> and expect being called if the right entry exists in the ACPI
> table.
> 
> A acpi_probe_device_init() is provided, taking an ACPI table
> identifier, and iterating over the registered entries.
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> ---
>  drivers/acpi/scan.c               | 41 ++++++++++++++++++++++++++++
>  include/asm-generic/vmlinux.lds.h | 11 ++++++++
>  include/linux/acpi.h              | 56 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 108 insertions(+)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index ec25635..9e920ec 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -2793,3 +2793,44 @@ int __init acpi_scan_init(void)
>  	mutex_unlock(&acpi_scan_lock);
>  	return result;
>  }
> +
> +static const struct acpi_probe_entry device_acpi_probe_end
> +		__used __section(__device_acpi_probe_table_end);
> +extern struct acpi_probe_entry __device_acpi_probe_table[];
> +static struct acpi_probe_entry *ape;
> +static int acpi_probe_count;
> +static DEFINE_SPINLOCK(acpi_probe_lock);
> +
> +static int __init acpi_match_madt(struct acpi_subtable_header *header,
> +				  const unsigned long end)
> +{
> +	if (!ape->validate_subtbl || ape->validate_subtbl(header, ape))
> +		if (!ape->probe_subtbl(header, end))
> +			acpi_probe_count++;
> +
> +	return 0;
> +}
> +
> +int __init acpi_probe_device_table(const char *id)
> +{
> +	int count = 0;
> +
> +	if (acpi_disabled)
> +		return 0;
> +
> +	spin_lock(&acpi_probe_lock);
> +	for (ape = __device_acpi_probe_table; ape->probe_table; ape++) {
> +		if (!ACPI_COMPARE_NAME(id, ape->id))
> +			continue;
> +		if (ACPI_COMPARE_NAME(ACPI_SIG_MADT, ape->id)) {
> +			acpi_probe_count = 0;
> +			acpi_table_parse_madt(ape->type, acpi_match_madt, 0);
> +			count += acpi_probe_count;
> +		} else {
> +			count = acpi_table_parse(ape->id, ape->probe_table);
> +		}
> +	}
> +	spin_unlock(&acpi_probe_lock);
> +
> +	return count;
> +}

We should add a mechanism to prevent re-parsing the same entries
multiple times (in case this function is called with the same
signature multiple times). We could create a separate table of device
entries, per-subsystem, that we want to parse (irqchip specific table,
timers, etc.) instead of adding all the devices to the same table (ie
linker section), you can do this already with the current patchset by
just choosing different table names as DT does.

We may also want to extend this set so that it can be used to parse the
same table, same subtype multiple times at different stages in the boot
path (but let's first see if it is a) really needed b) feasible).

Basically it is to avoid parsing the MADT multiple times:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/340267.html

Those can be extensions to the current patchset (because basically
they are not real issues at present), it is just a heads-up.

Thanks for putting it together !
Lorenzo

> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 8bd374d..875397a 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -181,6 +181,16 @@
>  #define CPUIDLE_METHOD_OF_TABLES() OF_TABLE(CONFIG_CPU_IDLE, cpuidle_method)
>  #define EARLYCON_OF_TABLES()	OF_TABLE(CONFIG_SERIAL_EARLYCON, earlycon)
>  
> +#ifdef CONFIG_ACPI
> +#define ACPI_PROBE_TABLE(name)						\
> +	. = ALIGN(8);							\
> +	VMLINUX_SYMBOL(__##name##_acpi_probe_table) = .;		\
> +	*(__##name##_acpi_probe_table)					\
> +	*(__##name##_acpi_probe_table_end)
> +#else
> +#define ACPI_PROBE_TABLE(name)
> +#endif
> +
>  #define KERNEL_DTB()							\
>  	STRUCT_ALIGN();							\
>  	VMLINUX_SYMBOL(__dtb_start) = .;				\
> @@ -516,6 +526,7 @@
>  	CPUIDLE_METHOD_OF_TABLES()					\
>  	KERNEL_DTB()							\
>  	IRQCHIP_OF_MATCH_TABLE()					\
> +	ACPI_PROBE_TABLE(device)					\
>  	EARLYCON_TABLE()						\
>  	EARLYCON_OF_TABLES()
>  
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index d2445fa..bf6dfb9 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -763,6 +763,52 @@ int acpi_dev_prop_read(struct acpi_device *adev, const char *propname,
>  
>  struct acpi_device *acpi_get_next_child(struct device *dev,
>  					struct acpi_device *child);
> +
> +struct acpi_probe_entry;
> +typedef bool (*acpi_probe_entry_validate_subtbl)(struct acpi_subtable_header *,
> +						 struct acpi_probe_entry *);
> +
> +#define ACPI_TABLE_ID_LEN	5
> +
> +/**
> + * struct acpi_probe_entry - boot-time probing entry
> + * @id:			ACPI table name
> + * @type:		Optional subtable type to match
> + *			(if @id contains subtables)
> + * @validate_subtbl:	Optional callback to check the validity of
> + *			the subtable
> + * @probe_table:	Callback to the driver being probed when table
> + *			match is successful
> + * @probe_subtbl:	Callback to the driver being probed when table and
> + *			subtable match (and optionnal callback is successful)
> + * @driver_data:	Sideband data provided back to the driver
> + */
> +struct acpi_probe_entry {
> +	__u8 id[ACPI_TABLE_ID_LEN];
> +	__u8 type;
> +	acpi_probe_entry_validate_subtbl validate_subtbl;
> +	union {
> +		acpi_tbl_table_handler probe_table;
> +		acpi_tbl_entry_handler probe_subtbl;
> +	};
> +	kernel_ulong_t driver_data;
> +};
> +
> +#define ACPI_DECLARE(table, name, table_id, subtable, valid, data, fn)	\
> +	static const struct acpi_probe_entry __acpi_probe_##name	\
> +		__used __section(__##table##_acpi_probe_table)		\
> +		 = {							\
> +			.id = table_id,					\
> +			.type = subtable,				\
> +			.validate_subtbl = valid,			\
> +			.probe_table = (acpi_tbl_table_handler)fn,	\
> +			.driver_data = data, 				\
> +		   }
> +
> +#define DEVICE_ACPI_DECLARE(name, table_id, fn)				\
> +	ACPI_DECLARE(device, name, table_id, 0, NULL, 0, fn)
> +
> +int acpi_probe_device_table(const char *id);
>  #else
>  static inline int acpi_dev_get_property(struct acpi_device *adev,
>  					const char *name, acpi_object_type type,
> @@ -813,6 +859,16 @@ static inline struct acpi_device *acpi_get_next_child(struct device *dev,
>  	return NULL;
>  }
>  
> +#define ACPI_DECLARE(table, name, table_id, subtable, validate, data, fn) \
> +	static const void * __acpi_table_##name[]			\
> +		__attribute__((unused))					\
> +		 = { (void *) table_id,					\
> +		     (void *) subtable,					\
> +		     (void *) valid,					\
> +		     (void *) fn,					\
> +		     (void *) data }
> +
> +static inline int acpi_probe_device_table(const char *id) { return 0; }
>  #endif
>  
>  #endif	/*_LINUX_ACPI_H*/
> -- 
> 2.1.4
>