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Message-ID: <8e3e945b-9cae-71e9-fc68-dc1c64e5ea86@nfschina.com>
Date: Tue, 18 Jul 2023 18:10:44 +0800
From: Su Hui <suhui@...china.com>
To: Dan Carpenter <dan.carpenter@...aro.org>,
Andrzej Hajda <andrzej.hajda@...el.com>
Cc: 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,
ville.syrjala@...ux.intel.com, mripard@...nel.org,
ankit.k.nautiyal@...el.com, intel-gfx@...ts.freedesktop.org,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drm/i915/tv: avoid possible division by zero
On 2023/7/18 13:39, Dan Carpenter wrote:
> On Mon, Jul 17, 2023 at 04:52:51PM +0200, Andrzej Hajda wrote:
>>
>> On 17.07.2023 08:22, Su Hui wrote:
>>> Clang warning: drivers/gpu/drm/i915/display/intel_tv.c:
>>> line 991, column 22 Division by zero.
>>> Assuming tv_mode->oversample=1 and (!tv_mode->progressive)=1,
>>> then division by zero will happen.
>>>
>>> Fixes: 1bba5543e4fe ("drm/i915: Fix TV encoder clock computation")
>>> Signed-off-by: Su Hui <suhui@...china.com>
>>> ---
>>> drivers/gpu/drm/i915/display/intel_tv.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/display/intel_tv.c b/drivers/gpu/drm/i915/display/intel_tv.c
>>> index 36b479b46b60..82b54af51f23 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_tv.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_tv.c
>>> @@ -988,7 +988,8 @@ 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);
>>> + mode->clock = clock / (tv_mode->oversample != 1 ?
>>> + tv_mode->oversample >> !tv_mode->progressive : 1);
>> Seems too smart to me, why not just:
>> mode->clock = clock / tv_mode->oversample;
>> if (!tv_mode->progressive)
>> mode->clock <<= 1;
> This is nice.
mode->clock = clock / tv_mode->oversample << !tv_mode->progressive;
But I think this one is much better, it has less code and run faster.
Should I resend v3 to add some explanation or follow Dan's advice?
Su Hui
> regards,
> dan carpenter
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