[ata] Make ATA command issuing partially asynchronous

Move the icky call to step() from aoe.c to ata.c; this takes it at
least one step further away from where it really doesn't belong.

Unfortunately, AoE has the ugly aoe_discover() mechanism which means
that we still have a step() loop in aoe.c for now; this needs to be
replaced at some future point.

src/drivers/block/ata.c

 #include <stddef.h>
 #include <string.h>
 #include <assert.h>
+#include <errno.h>
 #include <byteswap.h>
 #include <gpxe/blockdev.h>
+#include <gpxe/process.h>
 #include <gpxe/ata.h>
 
 /** @file
  */
 static inline __attribute__ (( always_inline )) int
 ata_command ( struct ata_device *ata, struct ata_command *command ) {
+	int rc;
+
 	DBG ( "ATA cmd %02x dev %02x LBA%s %llx count %04x\n",
 	      command->cb.cmd_stat, command->cb.device,
 	      ( command->cb.lba48 ? "48" : "" ),
 	      ( unsigned long long ) command->cb.lba.native,
 	      command->cb.count.native );
 
-	return ata->command ( ata, command );	
+	/* Flag command as in-progress */
+	command->rc = -EINPROGRESS;
+
+	/* Issue ATA command */
+	if ( ( rc = ata->command ( ata, command ) ) != 0 ) {
+		/* Something went wrong with the issuing mechanism */
+		DBG ( "ATA could not issue command: %s\n", strerror ( rc ) );
+		return rc;
+	}
+
+	/* Wait for command to complete */
+	while ( command->rc == -EINPROGRESS )
+		step();
+	if ( ( rc = command->rc ) != 0 ) {
+		/* Something went wrong with the command execution */
+		DBG ( "ATA command failed: %s\n", strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
 }
 
 /**

src/include/gpxe/ata.h

 	 * sectors in size.
 	 */
 	userptr_t data_in;
+	/** Command status code */
+	int rc;
 };
 
 /**

src/include/gpxe/errfile.h

 #define ERRFILE_arbel		     ( ERRFILE_DRIVER | 0x00710000 )
 #define ERRFILE_hermon		     ( ERRFILE_DRIVER | 0x00720000 )
 #define ERRFILE_linda		     ( ERRFILE_DRIVER | 0x00730000 )
+#define ERRFILE_ata		     ( ERRFILE_DRIVER | 0x00740000 )
 
 #define ERRFILE_aoe			( ERRFILE_NET | 0x00000000 )
 #define ERRFILE_arp			( ERRFILE_NET | 0x00010000 )

src/net/aoe.c

 	/* Record overall command status */
 	if ( aoe->command ) {
 		aoe->command->cb.cmd_stat = aoe->status;
+		aoe->command->rc = rc;
 		aoe->command = NULL;
 	}
 
 			 struct ata_command *command ) {
 	struct aoe_session *aoe =
 		container_of ( ata->backend, struct aoe_session, refcnt );
-	int rc;
 
 	aoe->command = command;
 	aoe->status = 0;
 
 	aoe_send_command ( aoe );
 
-	aoe->rc = -EINPROGRESS;
-	while ( aoe->rc == -EINPROGRESS )
-		step();
-	rc = aoe->rc;
-
-	return rc;
+	return 0;
 }
 
-
 /**
  * Issue AoE config query for AoE target discovery
  *