[Mesa-dev] [PATCH] i965: Extend the negative 32-bit deltas to 64-bits

[Sergii Romantsov]

Negative deltas are used to fake a range in a large buffer.
See 900a5c91eeb3
"i965: Use negative relocation deltas to minimise vertex uploads"

Gen8+ use 48-bit address relocations so need to extend the sign
to 64-bit return value. Without it we have higher bits zeroed
and missing the negavive values.
Haswell and older use 32-bit deltas so are unaffected by this issue.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101408
Signed-off-by: Sergii Romantsov <sergii.romantsov at globallogic.com>
Tested-by: Andriy Khulap <andriy.khulap at globallogic.com>
---
 src/mesa/drivers/dri/i965/intel_batchbuffer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.c b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
index d824ff2..128da77 100644
--- a/src/mesa/drivers/dri/i965/intel_batchbuffer.c
+++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
@@ -1124,8 +1124,10 @@ emit_reloc(struct intel_batchbuffer *batch,
    /* Using the old buffer offset, write in what the right data would be, in
     * case the buffer doesn't move and we can short-circuit the relocation
     * processing in the kernel
+    *
+    * Some target_offsets may be negative, so extend the sign to 64 bits.
     */
-   return entry->offset + target_offset;
+   return entry->offset + (int64_t)((int32_t)target_offset);
 }
 
 uint64_t
-- 
2.7.4