linux-kernel - re: drm/amd/display: make PSR static screen entry within 30 ms

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Date:   Fri, 17 Jan 2020 13:17:33 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Anthony Koo <Anthony.Koo@....com>,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        amd-gfx@...ts.freedesktop.org,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: drm/amd/display: make PSR static screen entry within 30 ms

Hi,

Static analysis with Coverity has detected a division by zero in the
following commit:

commit 5b5abe9526073ccbf3032d27b5864520829cdd9c
Author: Anthony Koo <Anthony.Koo@....com>
Date:   Mon Dec 9 17:26:34 2019 -0500

    drm/amd/display: make PSR static screen entry within 30 ms

Specifically:

       unsigned int vsync_rate_hz = 0;
       struct dc_static_screen_params params = {0};
       /* Calculate number of static frames before generating interrupt to
        * enter PSR.
        */
       unsigned int frame_time_microsec = 1000000 / vsync_rate_hz;

vsync_rate_hz is zero, and frame_time_microsec is being assigned a value
that is being divided by zero.  I'm not sure why this is coded this way
and not sure what the fix is, hence I'm reporting the issue.

Colin