From 52b53a0bf8026a322cfa6cfec6a10dd31fef8752 Mon Sep 17 00:00:00 2001 From: Ilija Hadzic Date: Thu, 2 Feb 2012 10:26:24 -0500 Subject: [PATCH] drm/radeon/kms/blit: fix blit copy for very large buffers MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Alex Deucher Reviewed-by: Michel Dänzer Signed-off-by: Dave Airlie --- drivers/gpu/drm/radeon/r600_blit_kms.c | 35 ++++++++++++++++++++++++---------- 1 file 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..accc032 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 ((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; } -- 2.7.4