Re: [PATCH 02/62] drm/i915/bdw: Handle forcewake for writes on gen8

Mika Kuoppala
2013-11-05T09:25:01Z

Ben Widawsky <benjamin.widawsky@intel.com> writes:

> GEN8 removes the GT FIFO which we've all come to know and love. Instead
> it offers a wider range of optimized registers which always keep a
> shadowed copy, and are fed to the GPU when it wakes.
>
> How this is implemented in hardware is still somewhat of a mystery. As
> far as I can tell, the basic design is as follows:
>
> If the register is not optimized, you must use the old forcewake
> mechanism to bring the GT out of sleep. [1]
>
> If register is in the optimized list the write will signal that the
> GT should begin to come out of whatever sleep state it is in.
>
> While the GT is coming out of sleep, the requested write will be stored
> in an intermediate shadow register.
>
> Do to the fact that the implementation details are not clear, I see
> several risks:
> 1. Order is not preserved as it is with GT FIFO. If we issue multiple
> writes to optimized registers, where order matters, we may need to
> serialize it with forcewake.
> 2. The optimized registers have only 1 shadowed slot, meaning if we
> issue multiple writes to the same register, and those values need to
> reach the GPU in order, forcewake will be required.
>
> [1] We could implement a SW queue the way the GT FIFO used to work if
> desired.
>
> NOTE: Compile tested only until we get real silicon.
>
> v2:
> - Use a default case to make future platforms also work.
> - Get rid of IS_BROADWELL since that's not yet defined, but we want to
> MMIO as soon as possible.
>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1)
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 53 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index f6fae35..fa06ce4 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -93,7 +93,7 @@ static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv)
> {
> u32 forcewake_ack;
>
> - if (IS_HASWELL(dev_priv->dev))
> + if (IS_HASWELL(dev_priv->dev) || IS_GEN8(dev_priv->dev))
> forcewake_ack = FORCEWAKE_ACK_HSW;
> else
> forcewake_ack = FORCEWAKE_MT_ACK;
> @@ -459,6 +459,47 @@ hsw_write##x(struct drm_i915_private *dev_priv, off_t reg, u##x val, bool trace)
> spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); \
> }
>
> +static const u32 gen8_optimized_regs[] = {
> + FORCEWAKE_MT,
> + GEN6_RPNSWREQ,
> + GEN6_RC_VIDEO_FREQ,
> + RING_TAIL(RENDER_RING_BASE),
> + RING_TAIL(GEN6_BSD_RING_BASE),
> + RING_TAIL(VEBOX_RING_BASE),
> + RING_TAIL(BLT_RING_BASE),
> + /* TODO: Other registers are not yet used */
> +};
> +

s/optimized/shadowed would make more sense i think.

> +static bool is_gen8_optimized(struct drm_i915_private *dev_priv, u32 reg)
> +{
> + int i;
> + for (i = 0; i < ARRAY_SIZE(gen8_optimized_regs); i++)
> + if (reg == gen8_optimized_regs[i])
> + return false;

The logic is reversed here with regards to function name.

> +
> + return true;
> +}
> +
> +#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 = false; \

This initialization is unnecessary.

> + REG_WRITE_HEADER; \
> + __needs_put = is_gen8_optimized(dev_priv, reg); \

This logic is backwards.
Please consider:

__needs_put = !is_gen8_shadowed(dev_priv, reg);

-- Mika

> + if (__needs_put) { \
> + dev_priv->uncore.funcs.force_wake_get(dev_priv); \
> + } \
> + __raw_i915_write##x(dev_priv, reg, val); \
> + if (__needs_put) { \
> + dev_priv->uncore.funcs.force_wake_put(dev_priv); \
> + } \
> + spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); \
> +}
> +
> +__gen8_write(8)
> +__gen8_write(16)
> +__gen8_write(32)
> +__gen8_write(64)
> __hsw_write(8)
> __hsw_write(16)
> __hsw_write(32)
> @@ -476,6 +517,7 @@ __gen4_write(16)
> __gen4_write(32)
> __gen4_write(64)
>
> +#undef __gen8_write
> #undef __hsw_write
> #undef __gen6_write
> #undef __gen5_write
> @@ -534,6 +576,15 @@ void intel_uncore_init(struct drm_device *dev)
> }
>
> switch (INTEL_INFO(dev)->gen) {
> + default:
> + dev_priv->uncore.funcs.mmio_writeb = gen8_write8;
> + dev_priv->uncore.funcs.mmio_writew = gen8_write16;
> + dev_priv->uncore.funcs.mmio_writel = gen8_write32;
> + dev_priv->uncore.funcs.mmio_writeq = gen8_write64;
> + dev_priv->uncore.funcs.mmio_readb = gen6_read8;
> + dev_priv->uncore.funcs.mmio_readw = gen6_read16;
> + dev_priv->uncore.funcs.mmio_readl = gen6_read32;
> + dev_priv->uncore.funcs.mmio_readq = gen6_read64;
> case 7:
> case 6:
> if (IS_HASWELL(dev)) {
> --
> 1.8.4.2
>
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