Hello Mathieu Malaterre,
The patch e9c0c874711b: "drm/dp: annotate implicit fall throughs" from Jan 14, 2019, leads to the following static checker warning:
drivers/gpu/drm/drm_dp_helper.c:495 drm_dp_downstream_max_bpc() warn: ignoring unreachable code.
drivers/gpu/drm/drm_dp_helper.c 467 int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE], 468 const u8 port_cap[4]) 469 { 470 int type = port_cap[0] & DP_DS_PORT_TYPE_MASK; 471 bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] & 472 DP_DETAILED_CAP_INFO_AVAILABLE; 473 int bpc; 474 475 if (!detailed_cap_info) 476 return 0; 477 478 switch (type) { 479 case DP_DS_PORT_TYPE_VGA: 480 case DP_DS_PORT_TYPE_DVI: 481 case DP_DS_PORT_TYPE_HDMI: 482 case DP_DS_PORT_TYPE_DP_DUALMODE: 483 bpc = port_cap[2] & DP_DS_MAX_BPC_MASK; ^^^^^^^^^^^^^^^^^^ This is 0x3.
484 485 switch (bpc) { 486 case DP_DS_8BPC: 487 return 8; 488 case DP_DS_10BPC: 489 return 10; 490 case DP_DS_12BPC: 491 return 12; 492 case DP_DS_16BPC: 493 return 16; 494 } 495 fallthrough;
This fallthrough is impossible. Probably the way to work around the bogus warning is the change the fallthough to "return 0; /* impossible */" otherwise the fallthrough is sort of misleading...
496 default: 497 return 0; 498 } 499 }
regards, dan carpenter