libata: implement libata.force module parameter

This patch implements libata.force module parameter which can
selectively override ATA port, link and device configurations
including cable type, SATA PHY SPD limit, transfer mode and NCQ.

For example, you can say "use 1.5Gbps for all fan-out ports attached
to the second port but allow 3.0Gbps for the PMP device itself, oh,
the device attached to the third fan-out port chokes on NCQ and
shouldn't go over UDMA4" by the following.

 libata.force=2:1.5g,2.15:3.0g,2.03:noncq,udma4
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

Documentation/kernel-parameters.txt

@@ -950,6 +950,41 @@ and is between 256 and 4096 characters. It is defined in the file
 			when set.
 			Format: <int>
 
+	libata.force=	[LIBATA] Force configurations.  The format is comma
+			separated list of "[ID:]VAL" where ID is
+			PORT[:DEVICE].  PORT and DEVICE are decimal numbers
+			matching port, link or device.  Basically, it matches
+			the ATA ID string printed on console by libata.  If
+			the whole ID part is omitted, the last PORT and DEVICE
+			values are used.  If ID hasn't been specified yet, the
+			configuration applies to all ports, links and devices.
+
+			If only DEVICE is omitted, the parameter applies to
+			the port and all links and devices behind it.  DEVICE
+			number of 0 either selects the first device or the
+			first fan-out link behind PMP device.  It does not
+			select the host link.  DEVICE number of 15 selects the
+			host link and device attached to it.
+
+			The VAL specifies the configuration to force.  As long
+			as there's no ambiguity shortcut notation is allowed.
+			For example, both 1.5 and 1.5G would work for 1.5Gbps.
+			The following configurations can be forced.
+
+			* Cable type: 40c, 80c, short40c, unk, ign or sata.
+			  Any ID with matching PORT is used.
+
+			* SATA link speed limit: 1.5Gbps or 3.0Gbps.
+
+			* Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
+			  udma[/][16,25,33,44,66,100,133] notation is also
+			  allowed.
+
+			* [no]ncq: Turn on or off NCQ.
+
+			If there are multiple matching configurations changing
+			the same attribute, the last one is used.
+
 	load_ramdisk=	[RAM] List of ramdisks to load from floppy
 			See Documentation/ramdisk.txt.
 

drivers/ata/libata-eh.c

@@ -2393,9 +2393,11 @@ static int ata_eh_revalidate_and_attach(struct ata_link *link,
 	}
 
 	/* PDIAG- should have been released, ask cable type if post-reset */
-	if (ata_is_host_link(link) && ap->ops->cable_detect &&
-	    (ehc->i.flags & ATA_EHI_DID_RESET))
+	if ((ehc->i.flags & ATA_EHI_DID_RESET) && ata_is_host_link(link)) {
+		if (ap->ops->cable_detect)
 			ap->cbl = ap->ops->cable_detect(ap);
+		ata_force_cbl(ap);
+	}
 
 	/* Configure new devices forward such that user doesn't see
 	 * device detection messages backwards.

drivers/ata/libata.h

@@ -61,6 +61,7 @@ extern int atapi_passthru16;
 extern int libata_fua;
 extern int libata_noacpi;
 extern int libata_allow_tpm;
+extern void ata_force_cbl(struct ata_port *ap);
 extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 			   u64 block, u32 n_block, unsigned int tf_flags,