drm/i915: Use a macro to express the range of valid gens for reg_read

The reg_read whitelist has a gen bitmask to code the gens we're allowing
the register to be read on. Until now, it was a literal, but we can be
a bit more expressive.

To ease the review, a small test program:

  $ cat bit-range.c
  #include <stdio.h>
  #include <stdint.h>

  #define U32_C(x)		x ## U
  #define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
  #define GEN_RANGE(l, h)	GENMASK(h, l)

  int main(int argc, char **argv)
  {
	printf("0x%08x\n", GEN_RANGE(1, 1));
	printf("0x%08x\n", GEN_RANGE(1, 2));
	printf("0x%08x\n", GEN_RANGE(4, 4));
	printf("0x%08x\n", GEN_RANGE(4, 5));
	printf("0x%08x\n", GEN_RANGE(1, 31));
	printf("0x%08x\n", GEN_RANGE(4, 8));

	return 0;
  }
  $ ./bit-range
  0x00000002
  0x00000006
  0x00000010
  0x00000030
  0xfffffffe
  0x000001f0

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_uncore.c

@@ -861,12 +861,15 @@ void intel_uncore_fini(struct drm_device *dev)
 	intel_uncore_forcewake_reset(dev, false);
 }
 
+#define GEN_RANGE(l, h) GENMASK(h, l)
+
 static const struct register_whitelist {
 	uint64_t offset;
 	uint32_t size;
-	uint32_t gen_bitmask; /* support gens, 0x10 for 4, 0x30 for 4 and 5, etc. */
+	/* supported gens, 0x10 for 4, 0x30 for 4 and 5, etc. */
+	uint32_t gen_bitmask;
 } whitelist[] = {
-	{ RING_TIMESTAMP(RENDER_RING_BASE), 8, 0x1F0 },
+	{ RING_TIMESTAMP(RENDER_RING_BASE), 8, GEN_RANGE(4, 8) },
 };
 
 int i915_reg_read_ioctl(struct drm_device *dev,