Coverity: intel_hti_uses_phy(): Integer handling issues

Hello!

This is an experimental semi-automated report about issues detected by Coverity from a scan of next-20221118 as part of the linux-next scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified lines of code (noted below) that were touched by commits:

Thu Nov 17 16:12:56 2022 +0200

    62749912540b ("drm/i915/display: move hti under display sub-struct")

Coverity reported the following:

*** CID 1527374: Integer handling issues (BAD_SHIFT) drivers/gpu/drm/i915/display/intel_hti.c:24 in intel_hti_uses_phy()

18     	if (INTEL_INFO(i915)->display.has_hti)
19     		i915->display.hti.state = intel_de_read(i915, HDPORT_STATE);
20     }

21
22 bool intel_hti_uses_phy(struct drm_i915_private *i915, enum phy phy)
23 {
vvv CID 1527374: Integer handling issues (BAD_SHIFT)
vvv In expression "1UL << 2 * phy + 1", shifting by a negative amount has undefined behavior. The shift amount, "2 * phy + 1", is as little as -1.

24     	return i915->display.hti.state & HDPORT_ENABLED &&
25     		i915->display.hti.state & HDPORT_DDI_USED(phy);
26     }

27
28 u32 intel_hti_dpll_mask(struct drm_i915_private *i915)
29 {

If this is a false positive, please let us know so we can mark it as such, or teach the Coverity rules to be smarter. If not, please make sure fixes get into linux-next. :) For patches fixing this, please include these lines (but double-check the "Fixes" first):

Addresses-Coverity-ID: 1527374 ("Integer handling issues")

This code appears to be safe currently (intel_hti_uses_phy() is never called with PHY_NONE), but perhaps add an explicit check?

	if (WARN_ON(phy == PHY_NONE))
		return false;

Thanks for your attention!

Coverity-bot

Thanks for the report, fix at [1].

I realize I didn't use the suggested tags above. For one thing, we've never really logged any proprietary tools used. Looks like "Addresses-Coverity-ID:" is growing in popularity though.

The Fixes: tag points at code refactoring, it was a pre-existing condition.

BR,
Jani.

[1] https://patchwork.freedesktop.org/patch/msgid/[email protected]

Jani Nikula, Intel Open Source Graphics Center