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[84.238.221.22]) by smtp.googlemail.com with ESMTPSA id u15sm2537567eds.6.2021.03.25.03.55.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Mar 2021 03:55:48 -0700 (PDT) Subject: Re: [PATCH] v4l: Cast timestamp tv_usec to singned To: Arnd Bergmann Cc: Linux Media Mailing List , Mauro Carvalho Chehab , Hans Verkuil References: <20210325102952.1126952-1-stanimir.varbanov@linaro.org> From: Stanimir Varbanov Message-ID: <29b4179f-b3d2-8c7e-eed6-af5aed80d430@linaro.org> Date: Thu, 25 Mar 2021 12:55:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On 3/25/21 12:51 PM, Arnd Bergmann wrote: > On Thu, Mar 25, 2021 at 11:29 AM Stanimir Varbanov > wrote: >> >> Some of the MPEG4 standards allows negative timestamps. Correct >> tv_usec cast to s32. >> >> Signed-off-by: Stanimir Varbanov > > Can you clarify what exactly is allowed in MPEG4? Normally we require > a normalized timestamp to come from user space in other kernel interfaces, > i.e. an arbitrary .tv_sec value that may or may not be negative, plus > a sub-second .tv_usec between 0 and 999999, or a .tv_nsect between 0 > and 999999999 to indicate the time after the last full second. > > E.g. a negative timestamp of -1.0001 seconds would be represented as > .tv_sec = -2, .tv_usec = 999900. Sure, I will try to collect some more info. Thanks! > > What is the range defined in MPEG4? It might be necessary to check > for the specific range and reject anything outside of that, in particular > if MPEG4 also allows positive microsecond values larger than 999999. > > Arnd > >> include/media/v4l2-common.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h >> index 3eb202259e8c..1ed61416003a 100644 >> --- a/include/media/v4l2-common.h >> +++ b/include/media/v4l2-common.h >> @@ -544,11 +544,11 @@ static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf) >> { >> /* >> * When the timestamp comes from 32-bit user space, there may be >> - * uninitialized data in tv_usec, so cast it to u32. >> + * uninitialized data in tv_usec, so cast it to s32. >> * Otherwise allow invalid input for backwards compatibility. >> */ >> return buf->timestamp.tv_sec * NSEC_PER_SEC + >> - (u32)buf->timestamp.tv_usec * NSEC_PER_USEC; >> + (s32)buf->timestamp.tv_usec * NSEC_PER_USEC; >> } >> -- regards, Stan