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SubjectRe: [PATCH v2 9/9] drm/bridge: ti-sn65dsi86: Avoid invalid rates
Hi Douglas,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v5.5-rc2 next-20191220]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url: https://github.com/0day-ci/linux/commits/Douglas-Anderson/drm-bridge-ti-sn65dsi86-Improve-support-for-AUO-B116XAK01-other-DP/20191221-083448
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 7e0165b2f1a912a06e381e91f0f4e495f4ac3736
config: sh-allmodconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 7.5.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
GCC_VERSION=7.5.0 make.cross ARCH=sh

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

drivers/gpu/drm/bridge/ti-sn65dsi86.c: In function 'ti_sn_bridge_enable':
>> drivers/gpu/drm/bridge/ti-sn65dsi86.c:543:18: warning: 'rate_valid' may be used uninitialized in this function [-Wmaybe-uninitialized]
if (rate_valid[i])
~~~~~~~~~~^~~

vim +/rate_valid +543 drivers/gpu/drm/bridge/ti-sn65dsi86.c

477
478 static void ti_sn_bridge_read_valid_rates(struct ti_sn_bridge *pdata,
479 bool rate_valid[])
480 {
481 u8 dpcd_val;
482 int rate_times_200khz;
483 int ret;
484 int i;
485
486 ret = drm_dp_dpcd_readb(&pdata->aux, DP_EDP_DPCD_REV, &dpcd_val);
487 if (ret != 1) {
488 DRM_DEV_ERROR(pdata->dev,
489 "Can't read eDP rev (%d), assuming 1.1\n", ret);
490 dpcd_val = DP_EDP_11;
491 }
492
493 if (dpcd_val >= DP_EDP_14) {
494 /* eDP 1.4 devices must provide a custom table */
495 __le16 sink_rates[DP_MAX_SUPPORTED_RATES];
496
497 ret = drm_dp_dpcd_read(&pdata->aux, DP_SUPPORTED_LINK_RATES,
498 sink_rates, sizeof(sink_rates));
499
500 if (ret != sizeof(sink_rates)) {
501 DRM_DEV_ERROR(pdata->dev,
502 "Can't read supported rate table (%d)\n", ret);
503
504 /* By zeroing we'll fall back to DP_MAX_LINK_RATE. */
505 memset(sink_rates, 0, sizeof(sink_rates));
506 }
507
508 for (i = 0; i < ARRAY_SIZE(sink_rates); i++) {
509 rate_times_200khz = le16_to_cpu(sink_rates[i]);
510
511 if (!rate_times_200khz)
512 break;
513
514 switch (rate_times_200khz) {
515 case 27000:
516 rate_valid[7] = 1;
517 break;
518 case 21600:
519 rate_valid[6] = 1;
520 break;
521 case 16200:
522 rate_valid[5] = 1;
523 break;
524 case 13500:
525 rate_valid[4] = 1;
526 break;
527 case 12150:
528 rate_valid[3] = 1;
529 break;
530 case 10800:
531 rate_valid[2] = 1;
532 break;
533 case 8100:
534 rate_valid[1] = 1;
535 break;
536 default:
537 /* unsupported */
538 break;
539 }
540 }
541
542 for (i = 0; i < ARRAY_SIZE(ti_sn_bridge_dp_rate_lut); i++) {
> 543 if (rate_valid[i])
544 return;
545 }
546 DRM_DEV_ERROR(pdata->dev,
547 "No matching eDP rates in table; falling back\n");
548 }
549
550 /* On older versions best we can do is use DP_MAX_LINK_RATE */
551 ret = drm_dp_dpcd_readb(&pdata->aux, DP_MAX_LINK_RATE, &dpcd_val);
552 if (ret != 1) {
553 DRM_DEV_ERROR(pdata->dev,
554 "Can't read max rate (%d); assuming 5.4 GHz\n",
555 ret);
556 dpcd_val = DP_LINK_BW_5_4;
557 }
558
559 switch (dpcd_val) {
560 default:
561 DRM_DEV_ERROR(pdata->dev,
562 "Unexpected max rate (%#x); assuming 5.4 GHz\n",
563 (int)dpcd_val);
564 /* fall through */
565 case DP_LINK_BW_5_4:
566 rate_valid[7] = 1;
567 /* fall through */
568 case DP_LINK_BW_2_7:
569 rate_valid[4] = 1;
570 /* fall through */
571 case DP_LINK_BW_1_62:
572 rate_valid[1] = 1;
573 break;
574 }
575 }
576

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation
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