Re: [PATCH v5 2/7] firmware: sysfb: Add helpers to unregister a pdev and disable registration

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Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
These can be used by subsystems to unregister a platform device registered
by sysfb and also to disable future platform device registration in sysfb.

Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---

(no changes since v4)

Changes in v4:
- Make sysfb_disable() to also attempt to unregister a device.

Changes in v2:
- Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).

  .../driver-api/firmware/other_interfaces.rst  |  6 ++
  drivers/firmware/sysfb.c                      | 87 +++++++++++++++++--
  include/linux/sysfb.h                         | 19 ++++
  3 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
index b81794e0cfbb..06ac89adaafb 100644
--- a/Documentation/driver-api/firmware/other_interfaces.rst
+++ b/Documentation/driver-api/firmware/other_interfaces.rst
@@ -13,6 +13,12 @@ EDD Interfaces
  .. kernel-doc:: drivers/firmware/edd.c
     :internal:
+Generic System Framebuffers Interface
+-------------------------------------
+
+.. kernel-doc:: drivers/firmware/sysfb.c
+   :export:
+
  Intel Stratix10 SoC Service Layer
  ---------------------------------
  Some features of the Intel Stratix10 SoC require a level of privilege
diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index b032f40a92de..6768968949e6 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -34,21 +34,92 @@
  #include <linux/screen_info.h>
  #include <linux/sysfb.h>
+static struct platform_device *pd;
+static DEFINE_MUTEX(disable_lock);
+static bool disabled;
+
+static bool sysfb_unregister(void)
+{
+	if (IS_ERR_OR_NULL(pd))
+		return false;
+
+	platform_device_unregister(pd);
+	pd = NULL;
+
+	return true;
+}
+
+/**
+ * sysfb_disable() - disable the Generic System Framebuffers support
+ *
+ * This disables the registration of system framebuffer devices that match the
+ * generic drivers that make use of the system framebuffer set up by firmware.
+ *
+ * It also unregisters a device if this was already registered by sysfb_init().

Why? I still cannot wrap my mind around, why we need to store *pd at all and use sysfb_try_unregister() for unregistering.

+ *
+ * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
+ *          against sysfb_init(), that registers a system framebuffer device and
+ *          sysfb_try_unregister(), that tries to unregister a framebuffer device.
+ */
+void sysfb_disable(void)
+{
+	mutex_lock(&disable_lock);
+	sysfb_unregister();
+	disabled = true;
+	mutex_unlock(&disable_lock);
+}
+EXPORT_SYMBOL_GPL(sysfb_disable);
+
+/**
+ * sysfb_try_unregister() - attempt to unregister a system framebuffer device
+ * @dev: device to unregister
+ *
+ * This tries to unregister a system framebuffer device if this was registered
+ * by the Generic System Framebuffers. The device will only be unregistered if
+ * it was registered by sysfb_init(), otherwise it will not be unregistered.
+ *
+ * Context: The function can sleep. a @load_lock mutex is acquired to serialize
+ *          against sysfb_init(), that registers a simple framebuffer device and
+ *          sysfb_disable(), that disables the Generic System Framebuffers support.
+ *
+ * Return:
+ * * true          - the device was unregistered successfully
+ * * false         - the device was not unregistered
+ */
+bool sysfb_try_unregister(struct device *dev)

As it stands, I strongly object the use of this function as still don't really get the purpose. It looks like a glorified wrapper around platform_device_unregister(). Do we need disable_lock to serialize with something else?

Best regards
Thomas


+{
+	bool ret = false;
+
+	mutex_lock(&disable_lock);
+	if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev))
+		goto unlock_mutex;
+
+	ret = sysfb_unregister();
+
+unlock_mutex:
+	mutex_unlock(&disable_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(sysfb_try_unregister);
+
  static __init int sysfb_init(void)
  {
  	struct screen_info *si = &screen_info;
  	struct simplefb_platform_data mode;
-	struct platform_device *pd;
  	const char *name;
  	bool compatible;
-	int ret;
+	int ret = 0;
+
+	mutex_lock(&disable_lock);
+	if (disabled)
+		goto unlock_mutex;
/* try to create a simple-framebuffer device */
  	compatible = sysfb_parse_mode(si, &mode);
  	if (compatible) {
  		pd = sysfb_create_simplefb(si, &mode);
  		if (!IS_ERR(pd))
-			return 0;
+			goto unlock_mutex;
  	}
/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +131,10 @@ static __init int sysfb_init(void)
  		name = "platform-framebuffer";
pd = platform_device_alloc(name, 0);
-	if (!pd)
-		return -ENOMEM;
+	if (!pd) {
+		ret = -ENOMEM;
+		goto unlock_mutex;
+	}
sysfb_apply_efi_quirks(pd); @@ -73,9 +146,11 @@ static __init int sysfb_init(void)
  	if (ret)
  		goto err;
- return 0;
+	goto unlock_mutex;
  err:
  	platform_device_put(pd);
+unlock_mutex:
+	mutex_unlock(&disable_lock);
  	return ret;
  }
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index 708152e9037b..e8c0313fac8f 100644
--- a/include/linux/sysfb.h
+++ b/include/linux/sysfb.h
@@ -55,6 +55,25 @@ struct efifb_dmi_info {
  	int flags;
  };
+#ifdef CONFIG_SYSFB
+
+void sysfb_disable(void);
+bool sysfb_try_unregister(struct device *dev);
+
+#else /* CONFIG_SYSFB */
+
+static inline void sysfb_disable(void)
+{
+
+}
+
+static inline bool sysfb_try_unregister(struct device *dev)
+{
+	return false;
+}
+
+#endif /* CONFIG_SYSFB */
+
  #ifdef CONFIG_EFI
extern struct efifb_dmi_info efifb_dmi_list[];

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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