[Intel-gfx] [PATCH 4/8] drm/i915: use the gmbus irq for waits

2012-09-09 Thread Daniel Vetter 
We need two special things to properly wire this up:
- Add another argument to gmbus_wait_hw_status to pass in the
  correct interrupt bit in gmbus4.
- Since we can only get an irq for one of the two events we want,
  hand-roll the wait_event_timeout code so that we wake up every
  jiffie and can check for NAKs. This way we also subsume gmbus
  support for platforms without interrupts (or where those are not
  yet enabled).

The important bit really is to only enable one gmbus interrupt source
at the same time - with that piece of lore figured out, this seems to
work flawlessly.

Ben Widawsky rightfully complained the lack of measurements for the
claimed benefits (especially since the first version was actually
broken and fell back to bit-banging). Previously reading the 256 byte
hdmi EDID takes about 72 ms here. With this patch it's down to 33 ms.
Given that transfering the 256 bytes over i2c at wire speed takes
20.5ms alone, the reduction in additional overhead is rather nice.

v2: Chris Wilson wondered whether GMBUS4 might contain some set bits
when booting up an hence result in some spurious interrupts. Since we
clear GMBUS4 after every wait and we do gmbus transfer really early in
the setup sequence to detect displays the window is small, but still
be paranoid and clear it properly.

v3: Clarify the comment that gmbus irq generation can only support one
kind of event, why it bothers us and how we work around that limit.

Cc: Daniel Kurtz djku...@chromium.org
Signed-off-by: Daniel Vetter daniel.vet...@ffwll.ch
---
 drivers/gpu/drm/i915/i915_drv.h  |  2 ++
 drivers/gpu/drm/i915/i915_irq.c  |  4 
 drivers/gpu/drm/i915/intel_i2c.c | 45 ++--
 3 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 26c6959..13b9e6a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -419,6 +419,8 @@ typedef struct drm_i915_private {
 */
uint32_t gpio_mmio_base;
 
+   wait_queue_head_t gmbus_wait_queue;
+
struct pci_dev *bridge_dev;
struct intel_ring_buffer ring[I915_NUM_RINGS];
uint32_t next_seqno;
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 86f1690..1741f2e 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -598,7 +598,11 @@ out:
 
 static void gmbus_irq_handler(struct drm_device *dev)
 {
+   struct drm_i915_private *dev_priv = (drm_i915_private_t *) 
dev-dev_private;
+
DRM_DEBUG_DRIVER(GMBUS interrupt\n);
+
+   wake_up_all(dev_priv-gmbus_wait_queue);
 }
 
 static void ibx_irq_handler(struct drm_device *dev, u32 pch_iir)
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 57decac..7413595 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -64,6 +64,7 @@ intel_i2c_reset(struct drm_device *dev)
 {
struct drm_i915_private *dev_priv = dev-dev_private;
I915_WRITE(dev_priv-gpio_mmio_base + GMBUS0, 0);
+   I915_WRITE(dev_priv-gpio_mmio_base + GMBUS4, 0);
 }
 
 static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool enable)
@@ -205,20 +206,38 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)
 
 static int
 gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
-u32 gmbus2_status)
+u32 gmbus2_status,
+u32 gmbus4_irq_en)
 {
-   int ret;
+   int i;
int reg_offset = dev_priv-gpio_mmio_base;
-   u32 gmbus2;
+   u32 gmbus2 = 0;
+   DEFINE_WAIT(wait);
+
+   /* Important: The hw handles only the first bit, so set only one! Since
+* we also need to check for NAKs besides the hw ready/idle signal, we
+* need to wake up periodically and check that ourselves. */
+   I915_WRITE(GMBUS4 + reg_offset, gmbus4_irq_en);
 
-   ret = wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) 
-  (GMBUS_SATOER | gmbus2_status),
-  50);
+   for (i = 0; i  msecs_to_jiffies(50) + 1; i++) {
+   prepare_to_wait(dev_priv-gmbus_wait_queue, wait,
+   TASK_UNINTERRUPTIBLE);
+
+   gmbus2 = I915_READ(GMBUS2 + reg_offset);
+   if (gmbus2  (GMBUS_SATOER | gmbus2_status))
+   break;
+
+   schedule_timeout(1);
+   }
+   finish_wait(dev_priv-gmbus_wait_queue, wait);
+
+   I915_WRITE(GMBUS4 + reg_offset, 0);
 
if (gmbus2  GMBUS_SATOER)
return -ENXIO;
-
-   return ret;
+   if (gmbus2  gmbus2_status)
+   return 0;
+   return -ETIMEDOUT;
 }
 
 static int
@@ -239,7 +258,8 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct 
i2c_msg *msg,
int ret;
u32 val, loop = 0;
 
-   ret = gmbus_wait_hw_status(dev_priv, GMBUS_HW_RDY);

Re: [Intel-gfx] [PATCH 4/8] drm/i915: use the gmbus irq for waits

2012-09-09 Thread Daniel Kurtz 
On Sun, Sep 9, 2012 at 5:00 PM, Daniel Vetter daniel.vet...@ffwll.ch wrote:

 We need two special things to properly wire this up:
 - Add another argument to gmbus_wait_hw_status to pass in the
   correct interrupt bit in gmbus4.
 - Since we can only get an irq for one of the two events we want,
   hand-roll the wait_event_timeout code so that we wake up every
   jiffie and can check for NAKs. This way we also subsume gmbus
   support for platforms without interrupts (or where those are not
   yet enabled).


Hi Daniel V,


 The important bit really is to only enable one gmbus interrupt source
 at the same time - with that piece of lore figured out, this seems to
 work flawlessly.

Great find!
Overall, this looks and sounds great.
See some comments inline...

 Ben Widawsky rightfully complained the lack of measurements for the
 claimed benefits (especially since the first version was actually
 broken and fell back to bit-banging). Previously reading the 256 byte
 hdmi EDID takes about 72 ms here. With this patch it's down to 33 ms.
 Given that transfering the 256 bytes over i2c at wire speed takes
 20.5ms alone, the reduction in additional overhead is rather nice.

 v2: Chris Wilson wondered whether GMBUS4 might contain some set bits
 when booting up an hence result in some spurious interrupts. Since we
 clear GMBUS4 after every wait and we do gmbus transfer really early in
 the setup sequence to detect displays the window is small, but still
 be paranoid and clear it properly.

 v3: Clarify the comment that gmbus irq generation can only support one
 kind of event, why it bothers us and how we work around that limit.

 Cc: Daniel Kurtz djku...@chromium.org
 Signed-off-by: Daniel Vetter daniel.vet...@ffwll.ch
 ---
  drivers/gpu/drm/i915/i915_drv.h  |  2 ++
  drivers/gpu/drm/i915/i915_irq.c  |  4 
  drivers/gpu/drm/i915/intel_i2c.c | 45 
 ++--
  3 files changed, 40 insertions(+), 11 deletions(-)

 diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
 index 26c6959..13b9e6a 100644
 --- a/drivers/gpu/drm/i915/i915_drv.h
 +++ b/drivers/gpu/drm/i915/i915_drv.h
 @@ -419,6 +419,8 @@ typedef struct drm_i915_private {
  */
 uint32_t gpio_mmio_base;

 +   wait_queue_head_t gmbus_wait_queue;
 +
 struct pci_dev *bridge_dev;
 struct intel_ring_buffer ring[I915_NUM_RINGS];
 uint32_t next_seqno;
 diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
 index 86f1690..1741f2e 100644
 --- a/drivers/gpu/drm/i915/i915_irq.c
 +++ b/drivers/gpu/drm/i915/i915_irq.c
 @@ -598,7 +598,11 @@ out:

  static void gmbus_irq_handler(struct drm_device *dev)
  {
 +   struct drm_i915_private *dev_priv = (drm_i915_private_t *) 
 dev-dev_private;
 +
 DRM_DEBUG_DRIVER(GMBUS interrupt\n);
 +
 +   wake_up_all(dev_priv-gmbus_wait_queue);
  }

  static void ibx_irq_handler(struct drm_device *dev, u32 pch_iir)
 diff --git a/drivers/gpu/drm/i915/intel_i2c.c 
 b/drivers/gpu/drm/i915/intel_i2c.c
 index 57decac..7413595 100644
 --- a/drivers/gpu/drm/i915/intel_i2c.c
 +++ b/drivers/gpu/drm/i915/intel_i2c.c
 @@ -64,6 +64,7 @@ intel_i2c_reset(struct drm_device *dev)
  {
 struct drm_i915_private *dev_priv = dev-dev_private;
 I915_WRITE(dev_priv-gpio_mmio_base + GMBUS0, 0);
 +   I915_WRITE(dev_priv-gpio_mmio_base + GMBUS4, 0);
  }

  static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool 
 enable)
 @@ -205,20 +206,38 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)

  static int
  gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
 -u32 gmbus2_status)
 +u32 gmbus2_status,
 +u32 gmbus4_irq_en)
  {
 -   int ret;
 +   int i;
 int reg_offset = dev_priv-gpio_mmio_base;
 -   u32 gmbus2;
 +   u32 gmbus2 = 0;


Technically, initializing gmbus2 here isn't necessary, since you
always assign it first before reading.


 +   DEFINE_WAIT(wait);
 +
 +   /* Important: The hw handles only the first bit, so set only one! 
 Since
 +* we also need to check for NAKs besides the hw ready/idle signal, we
 +* need to wake up periodically and check that ourselves. */


-- It is unfortunate that we can't enable both HW_WAIT/HW_RDY  NAK irqs.
When I tried it before, it seemed to work...  but something was always
unstable, and I never figured out what.


 +   I915_WRITE(GMBUS4 + reg_offset, gmbus4_irq_en);

 -   ret = wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) 
 -  (GMBUS_SATOER | gmbus2_status),
 -  50);
 +   for (i = 0; i  msecs_to_jiffies(50) + 1; i++) {


Should there be an initial check of our condition before entering the wait?


 +   prepare_to_wait(dev_priv-gmbus_wait_queue, wait,
 +   TASK_UNINTERRUPTIBLE);


Should this wait be interruptible?

 +
 +   gmbus2 =