[Intel-gfx] [PATCH v5 2/2] drm/i915: Simplify i915_reg_read_ioctl

[Chris Wilson]

Quoting Joonas Lahtinen (2017-09-11 10:59:01)
> Convert to use the freshly available made INTEL_GEN_MASK for easier
> grepping and improve function readability and clarify the UABI
> documentation.
> 
> No functional changes.
> 
> v2:
> - Lift GEM_BUG_ONs and use is_power_of_2 (Chris)
> - Retain -EINVAL on bad flags behavior (Chris)
> 
> v3:
> - Extract flags with 'entry->size - 1' (Chris)
> 
> v4:
> - Add GEM_BUG_ON on for flags vs entry offset (Chris)
> 
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 95 +++++++++++++++++--------------------
>  include/uapi/drm/i915_drm.h         |  6 ++-
>  2 files changed, 48 insertions(+), 53 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 1b38eb94d461..92420e0efa04 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1292,72 +1292,65 @@ void intel_uncore_fini(struct drm_i915_private *dev_priv)
>         intel_uncore_forcewake_reset(dev_priv, false);
>  }
>  
> -#define GEN_RANGE(l, h) GENMASK((h) - 1, (l) - 1)
> -
> -static const struct register_whitelist {
> -       i915_reg_t offset_ldw, offset_udw;
> -       uint32_t size;
> -       /* supported gens, 0x10 for 4, 0x30 for 4 and 5, etc. */
> -       uint32_t gen_bitmask;
> -} whitelist[] = {
> -       { .offset_ldw = RING_TIMESTAMP(RENDER_RING_BASE),
> -         .offset_udw = RING_TIMESTAMP_UDW(RENDER_RING_BASE),
> -         .size = 8, .gen_bitmask = GEN_RANGE(4, 10) },
> -};
> +static const struct reg_whitelist {
> +       i915_reg_t offset_ldw;
> +       i915_reg_t offset_udw;
> +       unsigned long gen_mask;
> +       u8 size;
> +} reg_read_whitelist[] = {{
> +       .offset_ldw = RING_TIMESTAMP(RENDER_RING_BASE),
> +       .offset_udw = RING_TIMESTAMP_UDW(RENDER_RING_BASE),
> +       .gen_mask = INTEL_GEN_MASK(4, 10),
> +       .size = 8
> +}};
>  
>  int i915_reg_read_ioctl(struct drm_device *dev,
>                         void *data, struct drm_file *file)
>  {
>         struct drm_i915_private *dev_priv = to_i915(dev);
>         struct drm_i915_reg_read *reg = data;
> -       struct register_whitelist const *entry = whitelist;
> -       unsigned size;
> -       i915_reg_t offset_ldw, offset_udw;
> -       int i, ret = 0;
> -
> -       for (i = 0; i < ARRAY_SIZE(whitelist); i++, entry++) {
> -               if (i915_mmio_reg_offset(entry->offset_ldw) == (reg->offset & -entry->size) &&
> -                   (INTEL_INFO(dev_priv)->gen_mask & entry->gen_bitmask))
> +       struct reg_whitelist const *entry;
> +       unsigned flags;
> +       int remain;
> +       int ret = 0;
> +
> +       entry = reg_read_whitelist;
> +       remain = ARRAY_SIZE(reg_read_whitelist);
> +       while (remain) {
> +               u32 entry_offset = i915_mmio_reg_offset(entry->offset_ldw);
> +
> +               GEM_BUG_ON(!is_power_of_2(entry->size));
> +               GEM_BUG_ON(entry->size > 8);
> +               GEM_BUG_ON(entry_offset & (entry->size - 1));
> +
> +               if (INTEL_INFO(dev_priv)->gen_mask & entry->gen_mask &&
> +                   entry_offset == (reg->offset & -entry->size))
>                         break;
> +               entry++;
> +               remain--;
>         }
>  
> -       if (i == ARRAY_SIZE(whitelist))
> +       if (!remain)
>                 return -EINVAL;

Thinking about the abi this would be nicer if it was ENOENT (continuing
our abuse) show that the caller can distinguish between a register not
existing. Bonus marks for -ENODEV.

e.g.:

ret = -ENOENT;
while (remain) {
	if (entry_offset != (reg->offset & -entry->size))
		continue;
	
	if (!INTEL_INFO(dev_priv)->gen_mask & entry->gem_mask) {
		ret = -ENODEV; /* known register, but bad gen */
		continue;
	}

	ret = 0;
	break;
}
if (ret)
	return ret;

Just thinking how to write an agnostic igt, you would start with

	igt_require(read_timestamp(fd) != -ENODEV);

so the test would naturally only run on the right hw. But there may be
some subtlety if registers are reassigned between gen...
-Chris