soundwire: intel_init: add kernel module parameter to filter out links

The hardware and ACPI info may report the presence of links that are
not physically enabled (e.g. due to pin-muxing or hardware reworks),
which in turn can result in errors being thrown. This shouldn't be the
case for production devices but will happen a lot on development
devices - even more so when they expose a connector.

Even when the ACPI information is correct, it's useful to be able to
only enable the links that need attention - mostly to filter out
dynamic debug messages.

Add a module parameter to filter out such links, e.g. adding the
following config to a file in /etc/modprobe.d will select the second
and third links only.

options soundwire_intel_init sdw_link_mask=0x6

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190806005522.22642-16-pierre-louis.bossart@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/intel_init.c

@@ -22,6 +22,10 @@
 #define SDW_LINK_BASE		0x30000
 #define SDW_LINK_SIZE		0x10000
 
+static int link_mask;
+module_param_named(sdw_link_mask, link_mask, int, 0444);
+MODULE_PARM_DESC(sdw_link_mask, "Intel link mask (one bit per link)");
+
 struct sdw_link_data {
 	struct sdw_intel_link_res res;
 	struct platform_device *pdev;
@@ -111,6 +115,13 @@ static struct sdw_intel_ctx
 
 	/* Create SDW Master devices */
 	for (i = 0; i < count; i++) {
+		if (link_mask && !(link_mask & BIT(i))) {
+			dev_dbg(&adev->dev,
+				"Link %d masked, will not be enabled\n", i);
+			link++;
+			continue;
+		}
+
 		link->res.irq = res->irq;
 		link->res.registers = res->mmio_base + SDW_LINK_BASE
 					+ (SDW_LINK_SIZE * i);