[bug report] drm/i915: Make sure we have enough memory bandwidth on ICL

Dan Carpenter
2019-05-29T10:05:45Z

Hi Syrjälä,

I had a question about commit c457d9cf256e: ("drm/i915: Make sure we have
enough memory bandwidth on ICL").

drivers/gpu/drm/i915/intel_bw.c
64 static int icl_pcode_read_qgv_point_info(struct drm_i915_private *dev_priv,
65 struct intel_qgv_point *sp,
66 int point)
67 {
68 u32 val = 0, val2;
^^^^
"val2" is uninitialized.

69 int ret;
70
71 ret = sandybridge_pcode_read(dev_priv,
72 ICL_PCODE_MEM_SUBSYSYSTEM_INFO |
73 ICL_PCODE_MEM_SS_READ_QGV_POINT_INFO(point),
74 &val, &val2);
75 if (ret)
76 return ret;
77
78 sp->dclk = val & 0xffff;
79 sp->t_rp = (val & 0xff0000) >> 16;
80 sp->t_rcd = (val & 0xff000000) >> 24;
81
82 sp->t_rdpre = val2 & 0xff;
83 sp->t_ras = (val2 & 0xff00) >> 8;
84
85 sp->t_rc = sp->t_rp + sp->t_ras;
86
87 return 0;
88 }

drivers/gpu/drm/i915/intel_sideband.c
376 static int __sandybridge_pcode_rw(struct drm_i915_private *i915,
377 u32 mbox, u32 *val, u32 *val1,
378 int fast_timeout_us,
379 int slow_timeout_ms,
380 bool is_read)
381 {
382 struct intel_uncore *uncore = &i915->uncore;
383
384 lockdep_assert_held(&i915->sb_lock);
385
386 /*
387 * GEN6_PCODE_* are outside of the forcewake domain, we can
388 * use te fw I915_READ variants to reduce the amount of work
389 * required when reading/writing.
390 */
391
392 if (intel_uncore_read_fw(uncore, GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY)
393 return -EAGAIN;
394
395 intel_uncore_write_fw(uncore, GEN6_PCODE_DATA, *val);
396 intel_uncore_write_fw(uncore, GEN6_PCODE_DATA1, val1 ? *val1 : 0);
^^^^^
We write uninitialized value out here. I'm sort of surprised that
UBSan doesn't complain. I don't know the code well enough to say if
this is a problem.

397 intel_uncore_write_fw(uncore,
398 GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
399
400 if (__intel_wait_for_register_fw(uncore,
401 GEN6_PCODE_MAILBOX,
402 GEN6_PCODE_READY, 0,
403 fast_timeout_us,
404 slow_timeout_ms,
405 &mbox))
406 return -ETIMEDOUT;

regards,
dan carpenter
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