[PATCH v2] misc: pvpanic: introduce device capability

[zhenwei pi <pizhenwei@bytedance.com>]

According to pvpanic spec:
https://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/specs/pvpanic.txt

The guest should determine pvpanic capability by RDPT, so initialize
capability during device probing. There is no need to register panic
notifier callback function if no events supported.

Before sending event to host side, check capability firstly.
Suggested by Paolo, export capability of pvpanic device by read-only
module parameter.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 drivers/misc/pvpanic.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
index 951b37da5e3c..c55a9d2fd001 100644
--- a/drivers/misc/pvpanic.c
+++ b/drivers/misc/pvpanic.c
@@ -19,6 +19,9 @@
 #include <uapi/misc/pvpanic.h>
 
 static void __iomem *base;
+static unsigned int capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
+module_param(capability, uint, 0444);
+MODULE_PARM_DESC(capability, "capability of pvpanic device");
 
 MODULE_AUTHOR("Hu Tao <hutao@cn.fujitsu.com>");
 MODULE_DESCRIPTION("pvpanic device driver");
@@ -27,7 +30,8 @@ MODULE_LICENSE("GPL");
 static void
 pvpanic_send_event(unsigned int event)
 {
-	iowrite8(event, base);
+	if (event & capability)
+		iowrite8(event, base);
 }
 
 static int
@@ -62,8 +66,12 @@ static int pvpanic_mmio_probe(struct platform_device *pdev)
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
-	atomic_notifier_chain_register(&panic_notifier_list,
-				       &pvpanic_panic_nb);
+	/* initlize capability by RDPT */
+	capability &= ioread8(base);
+
+	if (capability)
+		atomic_notifier_chain_register(&panic_notifier_list,
+					       &pvpanic_panic_nb);
 
 	return 0;
 }
@@ -71,8 +79,9 @@ static int pvpanic_mmio_probe(struct platform_device *pdev)
 static int pvpanic_mmio_remove(struct platform_device *pdev)
 {
 
-	atomic_notifier_chain_unregister(&panic_notifier_list,
-					 &pvpanic_panic_nb);
+	if (capability)
+		atomic_notifier_chain_unregister(&panic_notifier_list,
+						 &pvpanic_panic_nb);
 
 	return 0;
 }
-- 
2.25.1