libata: implement and use ops inheritance

libata lets low level drivers build ata_port_operations table and
register it with libata core layer.  This allows low level drivers
high level of flexibility but also burdens them with lots of
boilerplate entries.

This becomes worse for drivers which support related similar
controllers which differ slightly.  They share most of the operations
except for a few.  However, the driver still needs to list all
operations for each variant.  This results in large number of
duplicate entries, which is not only inefficient but also error-prone
as it becomes very difficult to tell what the actual differences are.

This duplicate boilerplates all over the low level drivers also make
updating the core layer exteremely difficult and error-prone.  When
compounded with multi-branched development model, it ends up
accumulating inconsistencies over time.  Some of those inconsistencies
cause immediate problems and fixed.  Others just remain there dormant
making maintenance increasingly difficult.

To rectify the problem, this patch implements ata_port_operations
inheritance.  To allow LLDs to easily re-use their own ops tables
overriding only specific methods, this patch implements poor man's
class inheritance.  An ops table has ->inherits field which can be set
to any ops table as long as it doesn't create a loop.  When the host
is started, the inheritance chain is followed and any operation which
isn't specified is taken from the nearest ancestor which has it
specified.  This operation is called finalization and done only once
per an ops table and the LLD doesn't have to do anything special about
it other than making the ops table non-const such that libata can
update it.

libata provides four base ops tables lower drivers can inherit from -
base, sata, pmp, sff and bmdma.  To avoid overriding these ops
accidentaly, these ops are declared const and LLDs should always
inherit these instead of using them directly.

After finalization, all the ops table are identical before and after
the patch except for setting .irq_handler to ata_interrupt in drivers
which didn't use to.  The .irq_handler doesn't have any actual effect
and the field will soon be removed by later patch.

* sata_sx4 is still using old style EH and currently doesn't take
  advantage of ops inheritance.

Signed-off-by: Tejun Heo <htejun@gmail.com>

1 files changed, 111 insertions, 2 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 394edf937cf..32fa9ee397b 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -74,6 +74,56 @@ const unsigned long sata_deb_timing_normal[]		= {   5,  100, 2000 };
 const unsigned long sata_deb_timing_hotplug[]		= {  25,  500, 2000 };
 const unsigned long sata_deb_timing_long[]		= { 100, 2000, 5000 };
 
+const struct ata_port_operations ata_base_port_ops = {
+	.irq_clear		= ata_noop_irq_clear,
+};
+
+const struct ata_port_operations sata_port_ops = {
+	.inherits		= &ata_base_port_ops,
+
+	.qc_defer		= ata_std_qc_defer,
+	.dev_select		= ata_noop_dev_select,
+};
+
+const struct ata_port_operations sata_pmp_port_ops = {
+	.inherits		= &sata_port_ops,
+};
+
+const struct ata_port_operations ata_sff_port_ops = {
+	.inherits		= &ata_base_port_ops,
+
+	.qc_prep		= ata_qc_prep,
+	.qc_issue		= ata_qc_issue_prot,
+
+	.freeze			= ata_bmdma_freeze,
+	.thaw			= ata_bmdma_thaw,
+	.error_handler		= ata_bmdma_error_handler,
+	.post_internal_cmd	= ata_bmdma_post_internal_cmd,
+
+	.dev_select		= ata_std_dev_select,
+	.check_status		= ata_check_status,
+	.tf_load		= ata_tf_load,
+	.tf_read		= ata_tf_read,
+	.exec_command		= ata_exec_command,
+	.data_xfer		= ata_data_xfer,
+	.irq_on			= ata_irq_on,
+
+	.port_start		= ata_sff_port_start,
+	.irq_handler		= ata_interrupt,
+};
+
+const struct ata_port_operations ata_bmdma_port_ops = {
+	.inherits		= &ata_sff_port_ops,
+
+	.mode_filter		= ata_pci_default_filter,
+
+	.bmdma_setup		= ata_bmdma_setup,
+	.bmdma_start		= ata_bmdma_start,
+	.bmdma_stop		= ata_bmdma_stop,
+	.bmdma_status		= ata_bmdma_status,
+	.irq_clear		= ata_bmdma_irq_clear,
+};
+
 static unsigned int ata_dev_init_params(struct ata_device *dev,
 					u16 heads, u16 sectors);
 static unsigned int ata_dev_set_xfermode(struct ata_device *dev);
@@ -6972,6 +7022,56 @@ static void ata_host_stop(struct device *gendev, void *res)
 }
 
 /**
+ *	ata_finalize_port_ops - finalize ata_port_operations
+ *	@ops: ata_port_operations to finalize
+ *
+ *	An ata_port_operations can inherit from another ops and that
+ *	ops can again inherit from another.  This can go on as many
+ *	times as necessary as long as there is no loop in the
+ *	inheritance chain.
+ *
+ *	Ops tables are finalized when the host is started.  NULL or
+ *	unspecified entries are inherited from the closet ancestor
+ *	which has the method and the entry is populated with it.
+ *	After finalization, the ops table directly points to all the
+ *	methods and ->inherits is no longer necessary and cleared.
+ *
+ *	Using ATA_OP_NULL, inheriting ops can force a method to NULL.
+ *
+ *	LOCKING:
+ *	None.
+ */
+static void ata_finalize_port_ops(struct ata_port_operations *ops)
+{
+	static spinlock_t lock = SPIN_LOCK_UNLOCKED;
+	const struct ata_port_operations *cur;
+	void **begin = (void **)ops;
+	void **end = (void **)&ops->inherits;
+	void **pp;
+
+	if (!ops || !ops->inherits)
+		return;
+
+	spin_lock(&lock);
+
+	for (cur = ops->inherits; cur; cur = cur->inherits) {
+		void **inherit = (void **)cur;
+
+		for (pp = begin; pp < end; pp++, inherit++)
+			if (!*pp)
+				*pp = *inherit;
+	}
+
+	for (pp = begin; pp < end; pp++)
+		if (IS_ERR(*pp))
+			*pp = NULL;
+
+	ops->inherits = NULL;
+
+	spin_unlock(&lock);
+}
+
+/**
  *	ata_host_start - start and freeze ports of an ATA host
  *	@host: ATA host to start ports for
  *
@@ -6996,9 +7096,13 @@ int ata_host_start(struct ata_host *host)
 	if (host->flags & ATA_HOST_STARTED)
 		return 0;
 
+	ata_finalize_port_ops(host->ops);
+
 	for (i = 0; i < host->n_ports; i++) {
 		struct ata_port *ap = host->ports[i];
 
+		ata_finalize_port_ops(ap->ops);
+
 		if (!host->ops && !ata_port_is_dummy(ap))
 			host->ops = ap->ops;
 
@@ -7060,7 +7164,7 @@ int ata_host_start(struct ata_host *host)
  */
 /* KILLME - the only user left is ipr */
 void ata_host_init(struct ata_host *host, struct device *dev,
-		   unsigned long flags, const struct ata_port_operations *ops)
+		   unsigned long flags, struct ata_port_operations *ops)
 {
 	spin_lock_init(&host->lock);
 	host->dev = dev;
@@ -7749,7 +7853,7 @@ static unsigned int ata_dummy_qc_issue(struct ata_queued_cmd *qc)
 	return AC_ERR_SYSTEM;
 }
 
-const struct ata_port_operations ata_dummy_port_ops = {
+struct ata_port_operations ata_dummy_port_ops = {
 	.check_status		= ata_dummy_check_status,
 	.check_altstatus	= ata_dummy_check_status,
 	.dev_select		= ata_noop_dev_select,
@@ -7777,6 +7881,11 @@ const struct ata_port_info ata_dummy_port_info = {
 EXPORT_SYMBOL_GPL(sata_deb_timing_normal);
 EXPORT_SYMBOL_GPL(sata_deb_timing_hotplug);
 EXPORT_SYMBOL_GPL(sata_deb_timing_long);
+EXPORT_SYMBOL_GPL(ata_base_port_ops);
+EXPORT_SYMBOL_GPL(sata_port_ops);
+EXPORT_SYMBOL_GPL(sata_pmp_port_ops);
+EXPORT_SYMBOL_GPL(ata_sff_port_ops);
+EXPORT_SYMBOL_GPL(ata_bmdma_port_ops);
 EXPORT_SYMBOL_GPL(ata_dummy_port_ops);
 EXPORT_SYMBOL_GPL(ata_dummy_port_info);
 EXPORT_SYMBOL_GPL(ata_std_bios_param);