From: "Pali Rohár" <pali@kernel.org> To: Geert Uytterhoeven <geert@linux-m68k.org> Cc: "Willy Tarreau" <w@1wt.eu>, "Michael Turquette" <mturquette@baylibre.com>, "Stephen Boyd" <sboyd@kernel.org>, "Rob Herring" <robh+dt@kernel.org>, "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>, "Andrew Lunn" <andrew@lunn.ch>, "Gregory Clement" <gregory.clement@bootlin.com>, "Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>, "Vladimir Vid" <vladimir.vid@sartura.hr>, "Marek Behún" <kabel@kernel.org>, linux-clk <linux-clk@vger.kernel.org>, "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "Linux ARM" <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Date: Fri, 25 Jun 2021 19:44:48 +0200 [thread overview] Message-ID: <20210625174448.kje4pvg5ixpu3vaw@pali> (raw) In-Reply-To: <CAMuHMdWfE7UKkp6=MdAVgHywFjDK3SN4m9+d_6AmJTB=qBEqFw@mail.gmail.com> On Friday 25 June 2021 19:39:10 Geert Uytterhoeven wrote: > Hi Willy, > > On Fri, Jun 25, 2021 at 5:50 PM Willy Tarreau <w@1wt.eu> wrote: > > On Fri, Jun 25, 2021 at 05:38:03PM +0200, Pali Rohár wrote: > > > On Friday 25 June 2021 17:22:31 Geert Uytterhoeven wrote: > > > > > +/* > > > > > + * DIV_U64_ROUND_CLOSEST - unsigned 64bit divide with 32bit divisor rounded to nearest integer > > > > > + * @dividend: unsigned 64bit dividend > > > > > + * @divisor: unsigned 32bit divisor > > > > > + * > > > > > + * Divide unsigned 64bit dividend by unsigned 32bit divisor > > > > > + * and round to closest integer. > > > > > + * > > > > > + * Return: dividend / divisor rounded to nearest integer > > > > > + */ > > > > > +#define DIV_U64_ROUND_CLOSEST(dividend, divisor) \ > > > > > + ({ u32 _tmp = (divisor); div_u64((u64)(dividend) + _tmp / 2, _tmp); }) > > > > > > > > Given "dividend" should already be an unsigned 64-bit value, I don't > > > > think the cast to "u64" is needed. Similar macros in this file also > > > > don't have the cast. > > > > > > It is just to ensure that plus operation between dividend and _tmp is > > > evaluated in 64-bit context to prevent overflow. Just a case when user > > > calls this macro with 32-bit dividend param. As it is a macro (and not > > > inline function) type is not automatically enforced. > > > > I agree, a large u32 argument added to _tmp/2 could overflow and remain > > 32 bits, yielding an incorrect result. The cast is mandatory here (and > > will either emit no code, or be useful). > > Fair enough. > So we want to add a cast to DIV64_U64_ROUND_CLOSEST() above, too? For DIV64_U64_ROUND_CLOSEST() it is not needed. divisor is copied into u64 _tmp variable and therefore "(dividend) + _tmp / 2" is already evaluated in 64-bit context even when dividend is only 32-bit. The only trap is that negative value as written below. > > The only trap I'm seeing is if a negative signed int is passed in dividend, > > it will be sign-extended and will give a large u64 value. A preliminary > > u32 cast could avoid this but would break valid u64 arguments, and I'd > > claim we never know what the user wants if this happens in the first place. > > Yep. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds
WARNING: multiple messages have this Message-ID (diff)
From: "Pali Rohár" <pali@kernel.org> To: Geert Uytterhoeven <geert@linux-m68k.org> Cc: "Willy Tarreau" <w@1wt.eu>, "Michael Turquette" <mturquette@baylibre.com>, "Stephen Boyd" <sboyd@kernel.org>, "Rob Herring" <robh+dt@kernel.org>, "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>, "Andrew Lunn" <andrew@lunn.ch>, "Gregory Clement" <gregory.clement@bootlin.com>, "Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>, "Vladimir Vid" <vladimir.vid@sartura.hr>, "Marek Behún" <kabel@kernel.org>, linux-clk <linux-clk@vger.kernel.org>, "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "Linux ARM" <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Date: Fri, 25 Jun 2021 19:44:48 +0200 [thread overview] Message-ID: <20210625174448.kje4pvg5ixpu3vaw@pali> (raw) In-Reply-To: <CAMuHMdWfE7UKkp6=MdAVgHywFjDK3SN4m9+d_6AmJTB=qBEqFw@mail.gmail.com> On Friday 25 June 2021 19:39:10 Geert Uytterhoeven wrote: > Hi Willy, > > On Fri, Jun 25, 2021 at 5:50 PM Willy Tarreau <w@1wt.eu> wrote: > > On Fri, Jun 25, 2021 at 05:38:03PM +0200, Pali Rohár wrote: > > > On Friday 25 June 2021 17:22:31 Geert Uytterhoeven wrote: > > > > > +/* > > > > > + * DIV_U64_ROUND_CLOSEST - unsigned 64bit divide with 32bit divisor rounded to nearest integer > > > > > + * @dividend: unsigned 64bit dividend > > > > > + * @divisor: unsigned 32bit divisor > > > > > + * > > > > > + * Divide unsigned 64bit dividend by unsigned 32bit divisor > > > > > + * and round to closest integer. > > > > > + * > > > > > + * Return: dividend / divisor rounded to nearest integer > > > > > + */ > > > > > +#define DIV_U64_ROUND_CLOSEST(dividend, divisor) \ > > > > > + ({ u32 _tmp = (divisor); div_u64((u64)(dividend) + _tmp / 2, _tmp); }) > > > > > > > > Given "dividend" should already be an unsigned 64-bit value, I don't > > > > think the cast to "u64" is needed. Similar macros in this file also > > > > don't have the cast. > > > > > > It is just to ensure that plus operation between dividend and _tmp is > > > evaluated in 64-bit context to prevent overflow. Just a case when user > > > calls this macro with 32-bit dividend param. As it is a macro (and not > > > inline function) type is not automatically enforced. > > > > I agree, a large u32 argument added to _tmp/2 could overflow and remain > > 32 bits, yielding an incorrect result. The cast is mandatory here (and > > will either emit no code, or be useful). > > Fair enough. > So we want to add a cast to DIV64_U64_ROUND_CLOSEST() above, too? For DIV64_U64_ROUND_CLOSEST() it is not needed. divisor is copied into u64 _tmp variable and therefore "(dividend) + _tmp / 2" is already evaluated in 64-bit context even when dividend is only 32-bit. The only trap is that negative value as written below. > > The only trap I'm seeing is if a negative signed int is passed in dividend, > > it will be sign-extended and will give a large u64 value. A preliminary > > u32 cast could avoid this but would break valid u64 arguments, and I'd > > claim we never know what the user wants if this happens in the first place. > > Yep. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-06-25 17:44 UTC|newest] Thread overview: 152+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-24 22:48 [PATCH 00/10] serial: mvebu-uart: Fixes and new support for higher baudrates Pali Rohár 2021-06-24 22:48 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 01/10] serial: mvebu-uart: fix calculation of clock divisor Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 02/10] serial: mvebu-uart: do not allow changing baudrate when uartclk is not available Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 03/10] serial: mvebu-uart: correctly calculate minimal possible baudrate Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 04/10] dt-bindings: mvebu-uart: fix documentation Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 05/10] arm64: dts: marvell: armada-37xx: Fix reg for standard variant of UART Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 06/10] serial: mvebu-uart: remove unused member nb from struct mvebu_uart Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 07/10] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-25 5:36 ` kernel test robot 2021-06-25 5:36 ` kernel test robot 2021-06-25 8:15 ` kernel test robot 2021-06-25 8:15 ` kernel test robot 2021-06-25 9:31 ` Pali Rohár 2021-06-25 9:31 ` Pali Rohár 2021-06-25 11:05 ` Geert Uytterhoeven 2021-06-25 11:05 ` Geert Uytterhoeven 2021-06-25 11:29 ` Pali Rohár 2021-06-25 11:29 ` Pali Rohár 2021-06-25 12:44 ` Geert Uytterhoeven 2021-06-25 12:44 ` Geert Uytterhoeven 2021-06-25 13:22 ` Pali Rohár 2021-06-25 13:22 ` Pali Rohár 2021-06-25 13:35 ` Geert Uytterhoeven 2021-06-25 13:35 ` Geert Uytterhoeven 2021-06-25 14:09 ` Pali Rohár 2021-06-25 14:09 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 08/10] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-06-24 22:49 ` [PATCH 08/10] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Pali Rohár 2021-06-24 22:49 ` [PATCH 09/10] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-24 22:49 ` [PATCH 10/10] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár 2021-06-24 22:49 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 00/11] serial: mvebu-uart: Fixes and new support for higher baudrates Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 01/11] serial: mvebu-uart: fix calculation of clock divisor Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 02/11] serial: mvebu-uart: do not allow changing baudrate when uartclk is not available Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 03/11] serial: mvebu-uart: correctly calculate minimal possible baudrate Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 04/11] dt-bindings: mvebu-uart: fix documentation Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 05/11] arm64: dts: marvell: armada-37xx: Fix reg for standard variant of UART Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 06/11] serial: mvebu-uart: remove unused member nb from struct mvebu_uart Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 15:22 ` Geert Uytterhoeven 2021-06-25 15:22 ` Geert Uytterhoeven 2021-06-25 15:38 ` Pali Rohár 2021-06-25 15:38 ` Pali Rohár 2021-06-25 15:50 ` Willy Tarreau 2021-06-25 15:50 ` Willy Tarreau 2021-06-25 17:39 ` Geert Uytterhoeven 2021-06-25 17:39 ` Geert Uytterhoeven 2021-06-25 17:44 ` Pali Rohár [this message] 2021-06-25 17:44 ` Pali Rohár 2021-06-25 18:11 ` Geert Uytterhoeven 2021-06-25 18:11 ` Geert Uytterhoeven 2021-07-19 12:45 ` Andy Shevchenko 2021-07-19 12:45 ` Andy Shevchenko 2021-06-25 14:36 ` [PATCH v2 08/11] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 09/11] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-06-25 14:36 ` [PATCH v2 09/11] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Pali Rohár 2021-06-25 14:36 ` [PATCH v2 10/11] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-06-25 14:36 ` [PATCH v2 11/11] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár 2021-06-25 14:36 ` Pali Rohár 2021-07-17 12:38 ` [PATCH v3 0/5] serial: mvebu-uart: Support for higher baudrates Pali Rohár 2021-07-17 12:38 ` Pali Rohár 2021-07-17 12:38 ` [PATCH v3 1/5] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár 2021-07-17 12:38 ` Pali Rohár 2021-07-19 12:47 ` Andy Shevchenko 2021-07-19 12:47 ` Andy Shevchenko 2021-07-22 21:57 ` Pali Rohár 2021-07-22 21:57 ` Pali Rohár 2021-07-24 11:38 ` David Laight 2021-07-24 11:38 ` David Laight 2021-07-17 12:38 ` [PATCH v3 2/5] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár 2021-07-17 12:38 ` Pali Rohár 2021-07-17 17:26 ` Andrew Lunn 2021-07-17 17:26 ` Andrew Lunn 2021-07-17 18:05 ` Pali Rohár 2021-07-17 18:05 ` Pali Rohár 2021-07-24 9:48 ` Pali Rohár 2021-07-24 9:48 ` Pali Rohár 2021-07-24 16:33 ` Andrew Lunn 2021-07-24 16:33 ` Andrew Lunn 2021-07-25 12:14 ` Pali Rohár 2021-07-25 12:14 ` Pali Rohár 2021-07-17 12:38 ` [PATCH v3 3/5] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-07-17 12:38 ` [PATCH v3 3/5] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Pali Rohár 2021-07-17 17:30 ` Andrew Lunn 2021-07-17 17:30 ` Andrew Lunn 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-07-17 12:38 ` [PATCH v3 4/5] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár 2021-07-17 12:38 ` Pali Rohár 2021-07-17 12:38 ` [PATCH v3 5/5] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár 2021-07-17 12:38 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 1/6] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 2/6] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-08-02 14:45 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Pali Rohár 2021-08-06 0:30 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Stephen Boyd 2021-08-06 0:30 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Stephen Boyd 2021-08-06 8:28 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-08-06 8:28 ` Pali Rohár 2021-08-12 19:33 ` Stephen Boyd 2021-08-12 19:33 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Stephen Boyd 2021-08-12 20:08 ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-08-12 20:08 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 4/6] dt-bindings: mvebu-uart: update information about UART clock Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 5/6] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-02 14:45 ` [PATCH v4 6/6] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár 2021-08-02 14:45 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 1/6] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 2/6] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár 2021-08-09 14:53 ` [PATCH v5 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Pali Rohár 2021-08-09 14:53 ` [PATCH v5 4/6] dt-bindings: mvebu-uart: update information about UART clock Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 5/6] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-09 14:53 ` [PATCH v5 6/6] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár 2021-08-09 14:53 ` Pali Rohár 2021-08-20 17:22 ` [PATCH v5 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár 2021-08-20 17:22 ` Pali Rohár 2021-08-31 8:35 ` Pali Rohár 2021-08-31 8:35 ` Pali Rohár 2021-09-21 7:41 ` Greg Kroah-Hartman 2021-09-21 7:41 ` Greg Kroah-Hartman
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20210625174448.kje4pvg5ixpu3vaw@pali \ --to=pali@kernel.org \ --cc=andrew@lunn.ch \ --cc=geert@linux-m68k.org \ --cc=gregkh@linuxfoundation.org \ --cc=gregory.clement@bootlin.com \ --cc=kabel@kernel.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-clk@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-serial@vger.kernel.org \ --cc=mturquette@baylibre.com \ --cc=robh+dt@kernel.org \ --cc=sboyd@kernel.org \ --cc=sebastian.hesselbarth@gmail.com \ --cc=vladimir.vid@sartura.hr \ --cc=w@1wt.eu \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.