dm/amdgpu: fix malformed link_settings debugfs output

[Why]
dp_link_settings_read() passed strlen() of each format string as the size
argument to snprintf() and then advanced rd_buf_ptr by that same fixed amount.
The format-string length has no relation to the formatted output length, so
snprintf() truncated each field at a NUL it wrote inside the buffer while the
pointer was advanced past it. The result is a buffer peppered with embedded NUL
bytes and fields that are silently cut short, so the data read back from the
debugfs node does not reflect the actual link settings.

[How]
Use scnprintf() with the real remaining buffer size
(rd_buf_size - (rd_buf_ptr - rd_buf)) and advance rd_buf_ptr by its return
value, which is the number of characters actually written. This both bounds
each write to the space left in rd_buf and keeps the output a single,
properly terminated string. The now-unused str_len local is removed.

Fixes: 41db5f1931ec ("drm/amd/display: set-read link rate and lane count through debugfs")
Assisted-by: Copilot:claude-opus-4.8
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 43b9f0f18693c7f7b75613f3aeae25fa2b4e2f76)
Cc: stable@vger.kernel.org

0 files changed, 0 insertions, 0 deletions