[PATCH 13/14] [media] ddbridge: Kconfig option to control the MSI modparam default

[Daniel Scheller <d.scheller.oss@gmail.com>]

From: Daniel Scheller <d.scheller@gmx.net>

It is known that MSI interrupts - while working quite well so far - can
still cause issues on some hardware platforms (causing I2C timeouts due
to unhandled interrupts). The msi variable/option is set to 1 by default.
So, add a Kconfig option prefixed with "EXPERIMENTAL" that will control
the default value of that modparam, defaulting to off for a better
user experience and (guaranteed) stable operation "per default".

Cc: Ralph Metzler <rjkm@metzlerbros.de>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
---
 drivers/media/pci/ddbridge/Kconfig         | 15 +++++++++++++++
 drivers/media/pci/ddbridge/ddbridge-main.c | 11 +++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/media/pci/ddbridge/Kconfig b/drivers/media/pci/ddbridge/Kconfig
index c79a58fa5fc3..1330b2ecc72a 100644
--- a/drivers/media/pci/ddbridge/Kconfig
+++ b/drivers/media/pci/ddbridge/Kconfig
@@ -26,3 +26,18 @@ config DVB_DDBRIDGE
 	  - CineS2 V7/V7A and DuoFlex S2 V4 (ST STV0910-based)
 
 	  Say Y if you own such a card and want to use it.
+
+config DVB_DDBRIDGE_MSIENABLE
+	bool "Enable Message Signaled Interrupts (MSI) per default (EXPERIMENTAL)"
+	depends on DVB_DDBRIDGE
+	depends on PCI_MSI
+	default n
+	---help---
+	  Use PCI MSI (Message Signaled Interrupts) per default. Enabling this
+	  might lead to I2C errors originating from the bridge in conjunction
+	  with certain SATA controllers, requiring a reload of the ddbridge
+	  module. MSI can still be disabled by passing msi=0 as option, as
+	  this will just change the msi option default value.
+
+	  If you're unsure, concerned about stability and don't want to pass
+	  module options in case of troubles, say N.
diff --git a/drivers/media/pci/ddbridge/ddbridge-main.c b/drivers/media/pci/ddbridge/ddbridge-main.c
index fa4f663c5acb..83643bc21d09 100644
--- a/drivers/media/pci/ddbridge/ddbridge-main.c
+++ b/drivers/media/pci/ddbridge/ddbridge-main.c
@@ -46,10 +46,17 @@ MODULE_PARM_DESC(adapter_alloc,
 		 "0-one adapter per io, 1-one per tab with io, 2-one per tab, 3-one for all");
 
 #ifdef CONFIG_PCI_MSI
+#ifdef CONFIG_DVB_DDBRIDGE_MSIENABLE
 int msi = 1;
+#else
+int msi;
+#endif
 module_param(msi, int, 0444);
-MODULE_PARM_DESC(msi,
-		 " Control MSI interrupts: 0-disable, 1-enable (default)");
+#ifdef CONFIG_DVB_DDBRIDGE_MSIENABLE
+MODULE_PARM_DESC(msi, "Control MSI interrupts: 0-disable, 1-enable (default)");
+#else
+MODULE_PARM_DESC(msi, "Control MSI interrupts: 0-disable (default), 1-enable");
+#endif
 #endif
 
 int ci_bitrate = 70000;
-- 
2.13.0