linux-kernel - Re: [RFT PATCH 5/7] gpio: exar: unduplicate address and offset computation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 26 Oct 2020 16:52:01 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [RFT PATCH 5/7] gpio: exar: unduplicate address and offset computation

On Mon, Oct 26, 2020 at 4:23 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> Provide and use helpers for calculating the register address and bit
> offset instead of hand coding it in every function.

Can you check code generation on x86, for example?

Sometimes compilers are eager to use idiv assembly instruction which
does simultaneously / and %.
I dunno if a) it's used for / 8 and % 8 since 8 is 2^3, b) splitting
to functions makes the above optimisation impossible.

> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>  drivers/gpio/gpio-exar.c | 40 ++++++++++++++++++++++++++++------------
>  1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpio/gpio-exar.c b/drivers/gpio/gpio-exar.c
> index db366d85b6b4..629f4dad6919 100644
> --- a/drivers/gpio/gpio-exar.c
> +++ b/drivers/gpio/gpio-exar.c
> @@ -33,6 +33,26 @@ struct exar_gpio_chip {
>         unsigned int first_pin;
>  };
>
> +static unsigned int
> +exar_offset_to_sel_addr(struct exar_gpio_chip *exar_gpio, unsigned int offset)
> +{
> +       return (offset + exar_gpio->first_pin) / 8 ? EXAR_OFFSET_MPIOSEL_HI
> +                                                  : EXAR_OFFSET_MPIOSEL_LO;
> +}
> +
> +static unsigned int
> +exar_offset_to_lvl_addr(struct exar_gpio_chip *exar_gpio, unsigned int offset)
> +{
> +       return (offset + exar_gpio->first_pin) / 8 ? EXAR_OFFSET_MPIOLVL_HI
> +                                                  : EXAR_OFFSET_MPIOLVL_LO;
> +}
> +
> +static unsigned int
> +exar_offset_to_bit(struct exar_gpio_chip *exar_gpio, unsigned int offset)
> +{
> +       return (offset + exar_gpio->first_pin) % 8;
> +}
> +
>  static void exar_update(struct gpio_chip *chip, unsigned int reg, int val,
>                         unsigned int offset)
>  {
> @@ -52,9 +72,8 @@ static int exar_set_direction(struct gpio_chip *chip, int direction,
>                               unsigned int offset)
>  {
>         struct exar_gpio_chip *exar_gpio = gpiochip_get_data(chip);
> -       unsigned int addr = (offset + exar_gpio->first_pin) / 8 ?
> -               EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
> -       unsigned int bit  = (offset + exar_gpio->first_pin) % 8;
> +       unsigned int addr = exar_offset_to_sel_addr(exar_gpio, offset);
> +       unsigned int bit = exar_offset_to_bit(exar_gpio, offset);
>
>         exar_update(chip, addr, direction, bit);
>         return 0;
> @@ -75,9 +94,8 @@ static int exar_get(struct gpio_chip *chip, unsigned int reg)
>  static int exar_get_direction(struct gpio_chip *chip, unsigned int offset)
>  {
>         struct exar_gpio_chip *exar_gpio = gpiochip_get_data(chip);
> -       unsigned int addr = (offset + exar_gpio->first_pin) / 8 ?
> -               EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
> -       unsigned int bit  = (offset + exar_gpio->first_pin) % 8;
> +       unsigned int addr = exar_offset_to_sel_addr(exar_gpio, offset);
> +       unsigned int bit = exar_offset_to_bit(exar_gpio, offset);
>
>         if (exar_get(chip, addr) & BIT(bit))
>                 return GPIO_LINE_DIRECTION_IN;
> @@ -88,9 +106,8 @@ static int exar_get_direction(struct gpio_chip *chip, unsigned int offset)
>  static int exar_get_value(struct gpio_chip *chip, unsigned int offset)
>  {
>         struct exar_gpio_chip *exar_gpio = gpiochip_get_data(chip);
> -       unsigned int addr = (offset + exar_gpio->first_pin) / 8 ?
> -               EXAR_OFFSET_MPIOLVL_HI : EXAR_OFFSET_MPIOLVL_LO;
> -       unsigned int bit  = (offset + exar_gpio->first_pin) % 8;
> +       unsigned int addr = exar_offset_to_lvl_addr(exar_gpio, offset);
> +       unsigned int bit = exar_offset_to_bit(exar_gpio, offset);
>
>         return !!(exar_get(chip, addr) & BIT(bit));
>  }
> @@ -99,9 +116,8 @@ static void exar_set_value(struct gpio_chip *chip, unsigned int offset,
>                            int value)
>  {
>         struct exar_gpio_chip *exar_gpio = gpiochip_get_data(chip);
> -       unsigned int addr = (offset + exar_gpio->first_pin) / 8 ?
> -               EXAR_OFFSET_MPIOLVL_HI : EXAR_OFFSET_MPIOLVL_LO;
> -       unsigned int bit  = (offset + exar_gpio->first_pin) % 8;
> +       unsigned int addr = exar_offset_to_sel_addr(exar_gpio, offset);
> +       unsigned int bit = exar_offset_to_bit(exar_gpio, offset);
>
>         exar_update(chip, addr, value, bit);
>  }
> --
> 2.29.1
>


-- 
With Best Regards,
Andy Shevchenko