Re: [PATCH v4 1/2] misc: pvpanic: introduce device capability

[Greg KH]

On Sun, Jan 10, 2021 at 01:37:18PM +0800, zhenwei pi wrote:
> 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 Greg KH, use sysfs to expose capability to user space,
> also add new sysfs attribute in document.
> 
> Signed-off-by: zhenwei pi 
> ---
>  .../ABI/testing/sysfs-bus-pci-devices-pvpanic |  7 
>  drivers/misc/pvpanic.c| 33 ---
>  2 files changed, 35 insertions(+), 5 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic 
> b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
> new file mode 100644
> index ..57d014a2c339
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
> @@ -0,0 +1,7 @@
> +What:/sys/devices/pci:00/*/QEMU0001:00/capability
> +Date:Jan 2021
> +Contact: zhenwei pi 
> +Description:
> + Read-only attribute. Capabilities of pvpanic device
> + which are supported by QEMU.
> + Format: %s.

Again, you are not saying exactly what the %s is, shouldn't you?  And
this does NOT match with the code below :(

> diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
> index 951b37da5e3c..c2f6a9e866b3 100644
> --- a/drivers/misc/pvpanic.c
> +++ b/drivers/misc/pvpanic.c
> @@ -19,6 +19,22 @@
>  #include 
>  
>  static void __iomem *base;
> +static unsigned int capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
> +
> +static ssize_t capability_show(struct device *dev,
> +struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%s%s",
> + capability & PVPANIC_PANICKED ? "PANICKED[BIT 0]\n" : "",
> + capability & PVPANIC_CRASH_LOADED ? "CRASH_LOADED[BIT 1]\n" : 
> "");

Why do you have "BIT X" in here?  Why would userspace care?

The rule for sysfs is "one value per file".  You just printed out
multiple lines.  Not good, and totally not allowed.

Also please use sysfs_emit().

thanks,

greg k-h

[PATCH v4 1/2] misc: pvpanic: introduce device capability

[zhenwei pi]

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 Greg KH, use sysfs to expose capability to user space,
also add new sysfs attribute in document.

Signed-off-by: zhenwei pi 
---
 .../ABI/testing/sysfs-bus-pci-devices-pvpanic |  7 
 drivers/misc/pvpanic.c| 33 ---
 2 files changed, 35 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic

diff --git a/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic 
b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
new file mode 100644
index ..57d014a2c339
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
@@ -0,0 +1,7 @@
+What:  /sys/devices/pci:00/*/QEMU0001:00/capability
+Date:  Jan 2021
+Contact:   zhenwei pi 
+Description:
+   Read-only attribute. Capabilities of pvpanic device
+   which are supported by QEMU.
+   Format: %s.
diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
index 951b37da5e3c..c2f6a9e866b3 100644
--- a/drivers/misc/pvpanic.c
+++ b/drivers/misc/pvpanic.c
@@ -19,6 +19,22 @@
 #include 
 
 static void __iomem *base;
+static unsigned int capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
+
+static ssize_t capability_show(struct device *dev,
+  struct device_attribute *attr, char *buf)
+{
+   return sprintf(buf, "%s%s",
+   capability & PVPANIC_PANICKED ? "PANICKED[BIT 0]\n" : "",
+   capability & PVPANIC_CRASH_LOADED ? "CRASH_LOADED[BIT 1]\n" : 
"");
+}
+static DEVICE_ATTR_RO(capability);
+
+static struct attribute *pvpanic_dev_attrs[] = {
+   &dev_attr_capability.attr,
+   NULL
+};
+ATTRIBUTE_GROUPS(pvpanic_dev);
 
 MODULE_AUTHOR("Hu Tao ");
 MODULE_DESCRIPTION("pvpanic device driver");
@@ -27,7 +43,8 @@ MODULE_LICENSE("GPL");
 static void
 pvpanic_send_event(unsigned int event)
 {
-   iowrite8(event, base);
+   if (event & capability)
+   iowrite8(event, base);
 }
 
 static int
@@ -62,8 +79,12 @@ 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 +92,9 @@ 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;
 }
@@ -93,6 +115,7 @@ static struct platform_driver pvpanic_mmio_driver = {
.name = "pvpanic-mmio",
.of_match_table = pvpanic_mmio_match,
.acpi_match_table = pvpanic_device_ids,
+   .dev_groups = pvpanic_dev_groups,
},
.probe = pvpanic_mmio_probe,
.remove = pvpanic_mmio_remove,
-- 
2.25.1