On Mon, Mar 18, 2013 at 04:56:02PM +0100, Jiri Kosina wrote:
> Okay, so I think that for 3.9 we want the patch below, and if eventually
> hardware root cause / workaround is found for GM45, we can have it merged
> later.
>
>
>
> From: Jiri Kosina <jkosina@xxxxxxx>
> Subject: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips
>
> Commit 28c70f162 ("drm/i915: use the gmbus irq for waits") switched to
> using GMBUS irqs instead of GPIO bit-banging for chipset generations 4
> and above.
>
> It turns out though that on many systems this leads to spurious interrupts
> being generated, long after the register write to disable the IRQs has been
> issued.
>
> Flushing of the register writes by POSTING_READ() directly after the register
> write doesn't work either.
>
> Disable using of GMBUS IRQs on Gen4 systems before the root cause is found and
> revert back to old behavior.
>
> Also be more careful about not issuing GMBUS4 register reads in
> gmbus_wait_hw_status() if we are not using GMBUS IRQs.
>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_i2c.c | 12 ++++++++++--
> 1 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index acf8aec..8638036 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -58,12 +58,14 @@ to_intel_gmbus(struct i2c_adapter *i2c)
> return container_of(i2c, struct intel_gmbus, adapter);
> }
>
> +#define HAS_GMBUS_IRQ(dev) (INTEL_INFO(dev)->gen >= 5)
> void
> 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);
> + if (HAS_GMBUS_IRQ(dev))
> + I915_WRITE(dev_priv->gpio_mmio_base + GMBUS4, 0);
There should not be any harm in always clearing GMBUS4, it exists on all
platforms.
> }
>
> static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool enable)
> @@ -203,7 +205,6 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)
> algo->data = bus;
> }
>
> -#define HAS_GMBUS_IRQ(dev) (INTEL_INFO(dev)->gen >= 4)
> static int
> gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
> u32 gmbus2_status,
> @@ -214,6 +215,13 @@ gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
> u32 gmbus2 = 0;
> DEFINE_WAIT(wait);
>
> + if (!HAS_GMBUS_IRQ(dev_priv->dev)) {
> + int ret;
> + ret = wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) &
> + (GMBUS_SATOER | gmbus2_status),
> + 50);
This should couple up to the normal return code that chooses the
appropriate return value based on gmbus2.
How about just using:
if (!HAS_GMBUS_IRQ(dev_priv->dev)) gmbus4_irq_en = 0;
and the existing wait loop?
> + return ret;
> + }
> /* 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. */
--
Chris Wilson, Intel Open Source Technology Centre
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