Re: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re:[3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interruptresponses))

[Chris Wilson]

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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