Re: [PATCH] drm/i915: Fix forcewake counts for gen8

[Ben Widawsky <benjamin.widawsky@intel.com>]

On Tue, Feb 18, 2014 at 07:10:24PM +0200, Mika Kuoppala wrote:
> Sometimes generic driver code gets forcewake explicitly by
> gen6_gt_force_wake_get(), which check forcewake_count before accessing
> hardware. However the register access with gen8_write function access
> low level hw accessors directly, ignoring the forcewake_count. This
> leads to nested forcewake get from hardware, in ring init and possibly
> elsewhere, causing forcewake ack clear errors and/or hangs.
> 
> Fix this by checking the forcewake count also in gen8_write
> 
> v2: Read side doesn't care about shadowed registers,
>     Remove __needs_put funkiness from gen8_write. (Ville)
>     Improved commit message.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=74007
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Ben Widawsky <benjamin.widawsky@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>

Thanks for finding this. I'd been meaning to track down the extra "Timed
out" messages. I do wonder how this actually fixes a hang. Do you have
any idea?

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>

> ---
>  drivers/gpu/drm/i915/intel_uncore.c |   19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index c628414..d1e9d63 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -634,16 +634,17 @@ static bool is_gen8_shadowed(struct drm_i915_private *dev_priv, u32 reg)
>  #define __gen8_write(x) \
>  static void \
>  gen8_write##x(struct drm_i915_private *dev_priv, off_t reg, u##x val, bool trace) { \
> -	bool __needs_put = reg < 0x40000 && !is_gen8_shadowed(dev_priv, reg); \
>  	REG_WRITE_HEADER; \
> -	if (__needs_put) { \
> -		dev_priv->uncore.funcs.force_wake_get(dev_priv, \
> -							FORCEWAKE_ALL); \
> -	} \
> -	__raw_i915_write##x(dev_priv, reg, val); \
> -	if (__needs_put) { \
> -		dev_priv->uncore.funcs.force_wake_put(dev_priv, \
> -							FORCEWAKE_ALL); \
> +	if (reg < 0x40000 && !is_gen8_shadowed(dev_priv, reg)) { \
> +		if (dev_priv->uncore.forcewake_count == 0) \
> +			dev_priv->uncore.funcs.force_wake_get(dev_priv,	\
> +							      FORCEWAKE_ALL); \
> +		__raw_i915_write##x(dev_priv, reg, val); \
> +		if (dev_priv->uncore.forcewake_count == 0) \
> +			dev_priv->uncore.funcs.force_wake_put(dev_priv, \
> +							      FORCEWAKE_ALL); \
> +	} else { \
> +		__raw_i915_write##x(dev_priv, reg, val); \
>  	} \
>  	REG_WRITE_FOOTER; \
>  }
> -- 
> 1.7.9.5
> 

-- 
Ben Widawsky, Intel Open Source Technology Center
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