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drm/radeon/kms/blit: fix blit copy for very large buffers 

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@daenzer.net for pointing out the root cause of
the bug.

v2: Fix I2F_MAX_INPUT constant definition goof and warn only once
    if input argument is out of range. Edit the comment a little
    bit to avoid some linguistic confusion and make it look better
    in general.

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Ilija Hadzic 2012-02-02 10:26:24 -05:00 committed by Dave Airlie
parent 304a48400d
commit 52b53a0bf8
1 changed files with 25 additions and 10 deletions
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35
drivers/gpu/drm/radeon/r600_blit_kms.c
View File

@ -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 ((1 << 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 the 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, respectively, 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_ONCE(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;
}