drm/i915/gmbus: fix spurious timeout on 512-byte burst reads

When reading exactly 512 bytes with burst read enabled, the
extra_byte_added path breaks out of the inner do-while without
decrementing len. The outer while(len) then re-enters and gmbus_wait()
times out since all data has been delivered. Decrement len before the
break so the outer loop terminates correctly.

Fixes: d5dc0f43f268 ("drm/i915/gmbus: Enable burst read")
Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patch.msgid.link/20260316231920.135438-2-samasth.norway.ananda@oracle.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 4ab0f09ee73fc853d00466682635f67c531f909c)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c b/drivers/gpu/drm/i915/display/intel_gmbus.c
index a7bce0c6a17e1348800798fc4cebbb8e3fa17345..264e6843bff1cf04fcaff74f580460dc3f9cbc8c 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_gmbus.c
+++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
@@ -496,8 +496,10 @@ gmbus_xfer_read_chunk(struct intel_display *display,
 
                val = intel_de_read_fw(display, GMBUS3(display));
                do {
-                       if (extra_byte_added && len == 1)
+                       if (extra_byte_added && len == 1) {
+                               len--;
                                break;
+                       }
 
                        *buf++ = val & 0xff;
                        val >>= 8;