vga_switcheroo: Add handler flags infrastructure

Allow handlers to declare their capabilities and allow clients to
obtain that information. So far we have these use cases:

* If the handler is able to switch DDC separately, clients need to
  probe EDID with drm_get_edid_switcheroo(). We should allow them
  to detect a capable handler to ensure this function only gets
  called when needed.

* Likewise if the handler is unable to switch AUX separately, the active
  client needs to communicate link training parameters to the inactive
  client, which may then skip the AUX handshake and set up its output
  with these pre-calibrated values (DisplayPort specification v1.1a,
  section 2.5.3.3). Clients need a way to recognize such a situation.

The flags for the radeon_atpx_handler and amdgpu_atpx_handler are
initially set to 0, this can later on be amended with
  handler_flags |= VGA_SWITCHEROO_CAN_SWITCH_DDC;
when a ->switch_ddc callback is added.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Lukas Wunner <lukas@wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina  15"]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/2b0d93ed6e511ca09e95e45e0b35627f330fabce.1452525860.git.lukas@wunner.de

1 files changed, 21 insertions, 1 deletions

diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index 665ab9f..e89f6ad 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -126,6 +126,7 @@ static DEFINE_MUTEX(vgasr_mutex);
  * 	(counting only vga clients, not audio clients)
  * @clients: list of registered clients
  * @handler: registered handler
+ * @handler_flags: flags of registered handler
  *
  * vga_switcheroo private data. Currently only one vga_switcheroo instance
  * per system is supported.
@@ -142,6 +143,7 @@ struct vgasr_priv {
 	struct list_head clients;
 
 	const struct vga_switcheroo_handler *handler;
+	enum vga_switcheroo_handler_flags_t handler_flags;
 };
 
 #define ID_BIT_AUDIO		0x100
@@ -190,13 +192,15 @@ static void vga_switcheroo_enable(void)
 /**
  * vga_switcheroo_register_handler() - register handler
  * @handler: handler callbacks
+ * @handler_flags: handler flags
  *
  * Register handler. Enable vga_switcheroo if two vga clients have already
  * registered.
  *
  * Return: 0 on success, -EINVAL if a handler was already registered.
  */
-int vga_switcheroo_register_handler(const struct vga_switcheroo_handler *handler)
+int vga_switcheroo_register_handler(const struct vga_switcheroo_handler *handler,
+				    enum vga_switcheroo_handler_flags_t handler_flags)
 {
 	mutex_lock(&vgasr_mutex);
 	if (vgasr_priv.handler) {
@@ -205,6 +209,7 @@ int vga_switcheroo_register_handler(const struct vga_switcheroo_handler *handler
 	}
 
 	vgasr_priv.handler = handler;
+	vgasr_priv.handler_flags = handler_flags;
 	if (vga_switcheroo_ready()) {
 		pr_info("enabled\n");
 		vga_switcheroo_enable();
@@ -222,6 +227,7 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler);
 void vga_switcheroo_unregister_handler(void)
 {
 	mutex_lock(&vgasr_mutex);
+	vgasr_priv.handler_flags = 0;
 	vgasr_priv.handler = NULL;
 	if (vgasr_priv.active) {
 		pr_info("disabled\n");
@@ -232,6 +238,20 @@ void vga_switcheroo_unregister_handler(void)
 }
 EXPORT_SYMBOL(vga_switcheroo_unregister_handler);
 
+/**
+ * vga_switcheroo_handler_flags() - obtain handler flags
+ *
+ * Helper for clients to obtain the handler flags bitmask.
+ *
+ * Return: Handler flags. A value of 0 means that no handler is registered
+ * or that the handler has no special capabilities.
+ */
+enum vga_switcheroo_handler_flags_t vga_switcheroo_handler_flags(void)
+{
+	return vgasr_priv.handler_flags;
+}
+EXPORT_SYMBOL(vga_switcheroo_handler_flags);
+
 static int register_client(struct pci_dev *pdev,
 			   const struct vga_switcheroo_client_ops *ops,
 			   enum vga_switcheroo_client_id id, bool active,