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.

Signed-off-by: Ilija Hadzic ihadzic@research.bell-labs.com --- 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; }