@@ -73,9 +73,19 @@
* there can thus be up to three clients: Two vga clients (GPUs) and one audio
* client (on the discrete GPU). The code is mostly prepared to support
* machines with more than two GPUs should they become available.
+ *
* The GPU to which the outputs are currently switched is called the
* active client in vga_switcheroo parlance. The GPU not in use is the
- * inactive client.
+ * inactive client. When the inactive client's DRM driver is loaded,
+ * it will be unable to probe the panel's EDID and hence depends on
+ * VBIOS to provide its display modes. If the VBIOS modes are bogus or
+ * if there is no VBIOS at all (which is common on the MacBook Pro),
+ * a client may alternatively request that the DDC lines are temporarily
+ * switched to it, provided that the handler supports this. Switching
+ * only the DDC lines and not the entire output avoids unnecessary
+ * flickering. On machines which are able to mux external connectors,
+ * VBIOS cannot know of attached displays so switching the DDC lines
+ * is the only option to retrieve the displays' EDID.
*/
/**
@@ -125,6 +135,7 @@ static DEFINE_MUTEX(vgasr_mutex);
* (counting only vga clients, not audio clients)
* @clients: list of registered clients
* @handler: registered handler
+ * @ddc_lock: protects access to DDC lines while they are temporarily switched
*
* vga_switcheroo private data. Currently only one vga_switcheroo instance
* per system is supported.
@@ -141,6 +152,7 @@ struct vgasr_priv {
struct list_head clients;
struct vga_switcheroo_handler *handler;
+ struct mutex ddc_lock;
};
#define ID_BIT_AUDIO 0x100
@@ -155,6 +167,7 @@ static void vga_switcheroo_debugfs_fini(struct vgasr_priv *priv);
/* only one switcheroo per system */
static struct vgasr_priv vgasr_priv = {
.clients = LIST_HEAD_INIT(vgasr_priv.clients),
+ .ddc_lock = __MUTEX_INITIALIZER(vgasr_priv.ddc_lock),
};
static bool vga_switcheroo_ready(void)
@@ -221,12 +234,14 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler);
void vga_switcheroo_unregister_handler(void)
{
mutex_lock(&vgasr_mutex);
+ mutex_lock(&vgasr_priv.ddc_lock);
vgasr_priv.handler = NULL;
if (vgasr_priv.active) {
pr_info("disabled\n");
vga_switcheroo_debugfs_fini(&vgasr_priv);
vgasr_priv.active = false;
}
+ mutex_unlock(&vgasr_priv.ddc_lock);
mutex_unlock(&vgasr_mutex);
}
EXPORT_SYMBOL(vga_switcheroo_unregister_handler);
@@ -414,6 +429,55 @@ void vga_switcheroo_client_fb_set(struct pci_dev *pdev,
EXPORT_SYMBOL(vga_switcheroo_client_fb_set);
/**
+ * vga_switcheroo_lock_ddc() - temporarily switch DDC lines to a given client
+ * @pdev: client pci device
+ *
+ * Temporarily switch DDC lines to the client identified by @pdev
+ * (but leave the outputs otherwise switched to where they are).
+ * This allows the inactive client to probe EDID. The DDC lines must
+ * afterwards be released by calling vga_switcheroo_unlock_ddc(),
+ * even if this function returns an error.
+ *
+ * Return: 0 on success or a negative int on error.
+ * Specifically, -ENODEV if no handler has registered or if the handler
+ * does not support switching the DDC lines. Also, a negative value
+ * returned by the handler is propagated back to the caller.
+ * The return value has merely an informational purpose for any caller
+ * which might be interested in it. It is acceptable to ignore the return
+ * value and simply rely on the result of the subsequent EDID probe,
+ * which will be NULL if DDC switching failed.
+ */
+int vga_switcheroo_lock_ddc(struct pci_dev *pdev)
+{
+ enum vga_switcheroo_client_id id;
+
+ mutex_lock(&vgasr_priv.ddc_lock);
+ if (!vgasr_priv.handler || !vgasr_priv.handler->switch_ddc)
+ return -ENODEV;
+
+ id = vgasr_priv.handler->get_client_id(pdev);
+ return vgasr_priv.handler->switch_ddc(id);
+}
+EXPORT_SYMBOL(vga_switcheroo_lock_ddc);
+
+/**
+ * vga_switcheroo_unlock_ddc() - release DDC lines after a temporary switch
+ *
+ * Release DDC lines after having temporarily switched them to a client.
+ * This must be called even if vga_switcheroo_lock_ddc() returned an error.
+ * Invoking this function without calling vga_switcheroo_lock_ddc() first
+ * is not allowed.
+ */
+void vga_switcheroo_unlock_ddc(void)
+{
+ if (WARN_ON_ONCE(!mutex_is_locked(&vgasr_priv.ddc_lock)))
+ return;
+
+ mutex_unlock(&vgasr_priv.ddc_lock);
+}
+EXPORT_SYMBOL(vga_switcheroo_unlock_ddc);
+
+/**
* DOC: Manual switching and manual power control
*
* In this mode of use, the file /sys/kernel/debug/vgaswitcheroo/switch
@@ -84,9 +84,12 @@ enum vga_switcheroo_client_id {
* vga clients. Currently only the radeon and amdgpu drivers use this.
* The return value is ignored
* @switchto: switch outputs to given client.
- * Mandatory. For muxless machines this should be a no-op. Returning 0
- * denotes success, anything else failure (in which case the switch is
- * aborted)
+ * Mandatory. For muxless machines this should be a no-op. If the mux
+ * is able to switch DDC separately, this should switch all pins except
+ * for the DDC lines. Returning 0 denotes success, anything else failure
+ * (in which case the switch is aborted)
+ * @switch_ddc: switch DDC lines to given client.
+ * Optional. Should return 0 on success or a negative int on failure
* @power_state: cut or reinstate power of given client.
* Optional. The return value is ignored
* @get_client_id: determine if given pci device is integrated or discrete GPU.
@@ -98,6 +101,7 @@ enum vga_switcheroo_client_id {
struct vga_switcheroo_handler {
int (*init)(void);
int (*switchto)(enum vga_switcheroo_client_id id);
+ int (*switch_ddc)(enum vga_switcheroo_client_id id);
int (*power_state)(enum vga_switcheroo_client_id id,
enum vga_switcheroo_state state);
enum vga_switcheroo_client_id (*get_client_id)(struct pci_dev *pdev);
@@ -140,6 +144,9 @@ void vga_switcheroo_client_fb_set(struct pci_dev *dev,
int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler);
void vga_switcheroo_unregister_handler(void);
+int vga_switcheroo_lock_ddc(struct pci_dev *pdev);
+void vga_switcheroo_unlock_ddc(void);
+
int vga_switcheroo_process_delayed_switch(void);
enum vga_switcheroo_state vga_switcheroo_get_client_state(struct pci_dev *dev);
@@ -160,6 +167,8 @@ static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
const struct vga_switcheroo_client_ops *ops,
enum vga_switcheroo_client_id id) { return 0; }
static inline void vga_switcheroo_unregister_handler(void) {}
+static inline int vga_switcheroo_lock_ddc(struct pci_dev *pdev) { return 0; }
+static inline void vga_switcheroo_unlock_ddc(void) {}
static inline int vga_switcheroo_process_delayed_switch(void) { return 0; }
static inline enum vga_switcheroo_state vga_switcheroo_get_client_state(struct pci_dev *dev) { return VGA_SWITCHEROO_ON; }
Originally by Seth Forshee <seth.forshee@canonical.com>, 2012-10-04: During graphics driver initialization it's useful to be able to mux only the DDC to the inactive client in order to read the EDID. Add a switch_ddc callback to allow capable handlers to provide this functionality, and add vga_switcheroo_switch_ddc() to allow DRM to mux only the DDC. Modified by Dave Airlie <airlied@gmail.com>, 2012-12-22: I can't figure out why I didn't like this, but I rewrote this [...] to lock/unlock the ddc lines [...]. I think I'd prefer something like that otherwise the interface got really ugly. Modified by Lukas Wunner <lukas@wunner.de>, 2015-08-14: Don't lock vgasr_mutex in _lock_ddc() / _unlock_ddc(), it can cause deadlocks because (a) during switch (with vgasr_mutex already held), GPU is woken and probes its outputs, tries to re-acquire vgasr_mutex to lock DDC lines; (b) Likewise during switch, GPU is suspended and calls cancel_delayed_work_sync() to stop output polling, if poll task is running at this moment we may wait forever for it to finish. Instead, lock ddc_lock when unregistering the handler because the only reason why we'd want to lock vgasr_mutex in _lock_ddc() / _unlock_ddc() is to block the handler from disappearing while DDC lines are switched. Don't switch DDC lines in stage2, it's pointless because if DDC is accessed, _lock_ddc() needs to be called anyway. And for consistency we'd also have to switch DDC on MIGD / MDIS commands and on runtime suspend, needlessly inflating the code. For the same reason it's unnecessary to switch DDC back to the previous owner on unlock. v2.1: Overhaul locking, squash commits (requested by Daniel Vetter <daniel.vetter@ffwll.ch>) v2.2: Readability improvements (requested by Thierry Reding <thierry.reding@gmail.com>) v2.3: Overhaul locking once more v2.4: Retain semantics of ->switchto handler callback to switch all pins (requested by Daniel Vetter <daniel.vetter@ffwll.ch>) v4: Drop DDC switch in stage2, MIGD / MDIS and runtime suspend 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"] Cc: Seth Forshee <seth.forshee@canonical.com> Cc: Dave Airlie <airlied@gmail.com> Signed-off-by: Lukas Wunner <lukas@wunner.de> --- drivers/gpu/vga/vga_switcheroo.c | 66 +++++++++++++++++++++++++++++++++++++++- include/linux/vga_switcheroo.h | 15 +++++++-- 2 files changed, 77 insertions(+), 4 deletions(-)