Originally by Seth Forshee <seth.forshee@xxxxxxxxxxxxx>, 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@xxxxxxxxx>, 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@xxxxxxxxx>, 2015-04 - 2015-10:
Change semantics of ->switch_ddc handler callback to return previous
DDC owner. Original version tried to determine previous DDC owner
with find_active_client() but this fails if the inactive client
registers before the active client.
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 mux_hw_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.
Also acquire mux_hw_lock in stage2 to avoid race condition where
reading the EDID and switching happens simultaneously. Likewise on
MIGD / MDIS commands and on runtime suspend.
v2.1: Overhaul locking, squash commits (Daniel Vetter)
v2.2: Readability improvements (Thierry Reding)
v2.3: Overhaul locking once more
v2.4: Retain semantics of ->switchto handler callback to switch all
pins, including DDC (Daniel Vetter)
v5: Rename ddc_lock to mux_hw_lock: Since we acquire this both
when calling ->switch_ddc and ->switchto, it protects not just
access to the DDC lines but to the mux in general. This is in
line with the DRM convention to use low-level locks to avoid
concurrent hw access (e.g. i2c, dp_aux) which are often called
hw_lock (Daniel Vetter)
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@xxxxxxxxx>
[MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina 15"]
Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxx>
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
drivers/gpu/vga/vga_switcheroo.c | 97 +++++++++++++++++++++++++++++++++++++++-
include/linux/vga_switcheroo.h | 8 ++++
2 files changed, 103 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index 81da941..56287ae 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -73,9 +73,17 @@
* 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.
*/
/**
@@ -126,6 +134,9 @@ static DEFINE_MUTEX(vgasr_mutex);
* @clients: list of registered clients
* @handler: registered handler
* @handler_flags: flags of registered handler
+ * @mux_hw_lock: protects mux state
+ * (in particular while DDC lines are temporarily switched)
+ * @old_ddc_owner: client to which DDC lines will be switched back on unlock
*
* vga_switcheroo private data. Currently only one vga_switcheroo instance
* per system is supported.
@@ -143,6 +154,8 @@ struct vgasr_priv {
const struct vga_switcheroo_handler *handler;
enum vga_switcheroo_handler_flags_t handler_flags;
+ struct mutex mux_hw_lock;
+ int old_ddc_owner;
};
#define ID_BIT_AUDIO 0x100
@@ -157,6 +170,7 @@ 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),
+ .mux_hw_lock = __MUTEX_INITIALIZER(vgasr_priv.mux_hw_lock),
};
static bool vga_switcheroo_ready(void)
@@ -226,6 +240,7 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler);
void vga_switcheroo_unregister_handler(void)
{
mutex_lock(&vgasr_mutex);
+ mutex_lock(&vgasr_priv.mux_hw_lock);
vgasr_priv.handler_flags = 0;
vgasr_priv.handler = NULL;
if (vgasr_priv.active) {
@@ -233,6 +248,7 @@ void vga_switcheroo_unregister_handler(void)
vga_switcheroo_debugfs_fini(&vgasr_priv);
vgasr_priv.active = false;
}
+ mutex_unlock(&vgasr_priv.mux_hw_lock);
mutex_unlock(&vgasr_mutex);
}
EXPORT_SYMBOL(vga_switcheroo_unregister_handler);
@@ -432,6 +448,76 @@ 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 switched back by calling vga_switcheroo_unlock_ddc(),
+ * even if this function returns an error.
+ *
+ * Return: Previous DDC owner 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.mux_hw_lock);
+ if (!vgasr_priv.handler || !vgasr_priv.handler->switch_ddc) {
+ vgasr_priv.old_ddc_owner = -ENODEV;
+ return -ENODEV;
+ }
+
+ id = vgasr_priv.handler->get_client_id(pdev);
+ vgasr_priv.old_ddc_owner = vgasr_priv.handler->switch_ddc(id);
+ return vgasr_priv.old_ddc_owner;
+}
+EXPORT_SYMBOL(vga_switcheroo_lock_ddc);
+
+/**
+ * vga_switcheroo_unlock_ddc() - switch DDC lines back to previous owner
+ * @pdev: client pci device
+ *
+ * Switch DDC lines back to the previous owner after calling
+ * vga_switcheroo_lock_ddc(). This must be called even if
+ * vga_switcheroo_lock_ddc() returned an error.
+ *
+ * Return: Previous DDC owner on success (i.e. the client identifier of @pdev)
+ * 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.
+ * Finally, invoking this function without calling vga_switcheroo_lock_ddc()
+ * first is not allowed and will result in %-EINVAL.
+ */
+int vga_switcheroo_unlock_ddc(struct pci_dev *pdev)
+{
+ enum vga_switcheroo_client_id id;
+ int ret = vgasr_priv.old_ddc_owner;
+
+ if (WARN_ON_ONCE(!mutex_is_locked(&vgasr_priv.mux_hw_lock)))
+ return -EINVAL;
+
+ if (vgasr_priv.old_ddc_owner >= 0) {
+ id = vgasr_priv.handler->get_client_id(pdev);
+ if (vgasr_priv.old_ddc_owner != id)
+ ret = vgasr_priv.handler->switch_ddc(
+ vgasr_priv.old_ddc_owner);
+ }
+ mutex_unlock(&vgasr_priv.mux_hw_lock);
+ return ret;
+}
+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
@@ -568,7 +654,9 @@ static int vga_switchto_stage2(struct vga_switcheroo_client *new_client)
console_unlock();
}
+ mutex_lock(&vgasr_priv.mux_hw_lock);
ret = vgasr_priv.handler->switchto(new_client->id);
+ mutex_unlock(&vgasr_priv.mux_hw_lock);
if (ret)
return ret;
@@ -683,7 +771,9 @@ vga_switcheroo_debugfs_write(struct file *filp, const char __user *ubuf,
vgasr_priv.delayed_switch_active = false;
if (just_mux) {
+ mutex_lock(&vgasr_priv.mux_hw_lock);
ret = vgasr_priv.handler->switchto(client_id);
+ mutex_unlock(&vgasr_priv.mux_hw_lock);
goto out;
}
@@ -895,8 +985,11 @@ static int vga_switcheroo_runtime_suspend(struct device *dev)
if (ret)
return ret;
mutex_lock(&vgasr_mutex);
- if (vgasr_priv.handler->switchto)
+ if (vgasr_priv.handler->switchto) {
+ mutex_lock(&vgasr_priv.mux_hw_lock);
vgasr_priv.handler->switchto(VGA_SWITCHEROO_IGD);
+ mutex_unlock(&vgasr_priv.mux_hw_lock);
+ }
vga_switcheroo_power_switch(pdev, VGA_SWITCHEROO_OFF);
mutex_unlock(&vgasr_mutex);
return 0;
diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h
index a745f4f0..b39a5f3 100644
--- a/include/linux/vga_switcheroo.h
+++ b/include/linux/vga_switcheroo.h
@@ -102,6 +102,9 @@ enum vga_switcheroo_client_id {
* Mandatory. For muxless machines this should be a no-op. 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 the previous DDC owner 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.
@@ -113,6 +116,7 @@ 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);
@@ -156,6 +160,8 @@ int vga_switcheroo_register_handler(const struct vga_switcheroo_handler *handler
enum vga_switcheroo_handler_flags_t handler_flags);
void vga_switcheroo_unregister_handler(void);
enum vga_switcheroo_handler_flags_t vga_switcheroo_handler_flags(void);
+int vga_switcheroo_lock_ddc(struct pci_dev *pdev);
+int vga_switcheroo_unlock_ddc(struct pci_dev *pdev);
int vga_switcheroo_process_delayed_switch(void);
@@ -179,6 +185,8 @@ static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
enum vga_switcheroo_client_id id) { return 0; }
static inline void vga_switcheroo_unregister_handler(void) {}
static inline enum vga_switcheroo_handler_flags_t vga_switcheroo_handler_flags(void) { return 0; }
+static inline int vga_switcheroo_lock_ddc(struct pci_dev *pdev) { return -ENODEV; }
+static inline int vga_switcheroo_unlock_ddc(struct pci_dev *pdev) { return -ENODEV; }
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; }
--
1.8.5.2 (Apple Git-48)
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