Evergreen and NI blit copy was broken if the buffer maps to a rectangle
whose one dimension is 16384 (max dimension allowed by these chips).
In the mainline kernel, the problem is exposed only when buffers are
very large (1G), but it's still a problem. The problem could be exposed
for smaller buffers if anyone modifies the algorithm for rectangle
construction in r600_blit_create_rect() (the reason why someone would
modify that algorithm is to tune the performance of buffer moves).
The root cause was in i2f() function which only operated on range between
0 and 16383. Fix this by extending the range of i2f() function to 0 to
32767.
While at it improve the function so that the range can be easily
extended in the future (if it becomes necessary), cleanup lines
over 80 characters, and replace in-line comments with one strategic
comment that explains the crux of the function.
Credits to michel@xxxxxxxxxxx for pointing out the root cause of
the bug.
Signed-off-by: Ilija Hadzic <ihadzic@xxxxxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/radeon/r600_blit_kms.c | 35 ++++++++++++++++++++++---------
1 files changed, 25 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/radeon/r600_blit_kms.c b/drivers/gpu/drm/radeon/r600_blit_kms.c
index d996f43..32dcc95 100644
--- a/drivers/gpu/drm/radeon/r600_blit_kms.c
+++ b/drivers/gpu/drm/radeon/r600_blit_kms.c
@@ -468,27 +468,42 @@ set_default_state(struct radeon_device *rdev)
radeon_ring_write(ring, sq_stack_resource_mgmt_2);
}
+#define I2F_MAX_BITS 15
+#define I2F_MAX_INPUT ((2 << I2F_MAX_BITS) - 1)
+#define I2F_SHIFT (24 - I2F_MAX_BITS)
+
+/*
+ * converts unsigned integer into 32-bit IEEE floating point representation;
+ * conversion is not universal and only works for the range from 0
+ * to 2^^I2F_MAX_BITS-1; currently we only use it with inputs between
+ * 0 and 16384 (inclusive), so I2F_MAX_BITS=15 is enough; if necessary
+ * I2F_MAX_BITS can be increased, but that will add to loop iterations
+ * and slow us down; conversion is done by shifting the input and counting
+ * down until the first 1 reaches bit position 23; the resulting counter
+ * and the shifted input are the exponent and the fraction; the sign is
+ * always zero
+ */
static uint32_t i2f(uint32_t input)
{
u32 result, i, exponent, fraction;
- if ((input & 0x3fff) == 0)
- result = 0; /* 0 is a special case */
+ WARN_ON(input > I2F_MAX_INPUT);
+
+ if ((input & I2F_MAX_INPUT) == 0)
+ result = 0;
else {
- exponent = 140; /* exponent biased by 127; */
- fraction = (input & 0x3fff) << 10; /* cheat and only
- handle numbers below 2^^15 */
- for (i = 0; i < 14; i++) {
+ exponent = 126 + I2F_MAX_BITS;
+ fraction = (input & I2F_MAX_INPUT) << I2F_SHIFT;
+
+ for (i = 0; i < I2F_MAX_BITS; i++) {
if (fraction & 0x800000)
break;
else {
- fraction = fraction << 1; /* keep
- shifting left until top bit = 1 */
+ fraction = fraction << 1;
exponent = exponent - 1;
}
}
- result = exponent << 23 | (fraction & 0x7fffff); /* mask
- off top bit; assumed 1 */
+ result = exponent << 23 | (fraction & 0x7fffff);
}
return result;
}
--
1.7.7
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