linux-kernel - Re: [Intel-gfx] [PATCH v2] drm/i915/tv: avoid possible division by zero

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Message-ID: <5d096bcf-c394-4dad-b307-3d7e33ab6e6f@kadam.mountain>
Date:   Tue, 25 Jul 2023 08:51:50 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Su Hui <suhui@...china.com>
Cc:     Andi Shyti <andi.shyti@...ux.intel.com>,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        airlied@...il.com, daniel@...ll.ch, nathan@...nel.org,
        ndesaulniers@...gle.com, trix@...hat.com, andrzej.hajda@...el.com,
        intel-gfx@...ts.freedesktop.org, llvm@...ts.linux.dev,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, mripard@...nel.org
Subject: Re: [Intel-gfx] [PATCH v2] drm/i915/tv: avoid possible division by
 zero

The reason why the first five attempts had bugs is because we are
trying to write it in the most complicated way possible, shifting by
logical not what?

regards,
dan carpenter

diff --git a/drivers/gpu/drm/i915/display/intel_tv.c b/drivers/gpu/drm/i915/display/intel_tv.c
index 36b479b46b60..6997b6cb1df2 100644
--- a/drivers/gpu/drm/i915/display/intel_tv.c
+++ b/drivers/gpu/drm/i915/display/intel_tv.c
@@ -988,7 +988,13 @@ intel_tv_mode_to_mode(struct drm_display_mode *mode,
 		      const struct tv_mode *tv_mode,
 		      int clock)
 {
-	mode->clock = clock / (tv_mode->oversample >> !tv_mode->progressive);
+	int div = tv_mode->oversample;
+
+	if (!tv_mode->progressive)
+		div >>= 1;
+	if (div == 0)
+		div = 1;
+	mode->clock = clock / div;
 
 	/*
 	 * tv_mode horizontal timings:
@@ -1135,6 +1141,8 @@ intel_tv_get_config(struct intel_encoder *encoder,
 		break;
 	default:
 		tv_mode.oversample = 1;
+		WARN_ON_ONCE(!tv_mode.progressive);
+		tv_mode.progressive = true;
 		break;
 	}