On Tue, 25 Aug 2020, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> 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...
Won't that be unreachable as well?
Maybe just add the default label to switch (bpc)?
BR,
Jani.
>
> 496 default:
> 497 return 0;
> 498 }
> 499 }
>
> regards,
> dan carpenter
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--
Jani Nikula, Intel Open Source Graphics Center
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