linux-kernel - Re: [PATCH v7 3/3] gpio: pca953x: fix address calculation for pcal6524

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Date:   Wed, 23 May 2018 16:06:36 +0200
From:   Pavel Machek <pavel@....cz>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     galak@...eaurora.org, andy.shevchenko@...il.com,
        Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com
Subject: Re: [PATCH v7 3/3] gpio: pca953x: fix address calculation for
 pcal6524

On Thu 2018-05-17 06:59:49, H. Nikolaus Schaller wrote:
> The register constants are so far defined in a way that they fit
> for the pcal9555a when shifted by the number of banks, i.e. are
> multiplied by 2 in the accessor function.
> 
> Now, the pcal6524 has 3 banks which means the relative offset
> is multiplied by 4 for the standard registers.
> 
> Simply applying the bit shift to the extended registers gives
> a wrong result, since the base offset is already included in
> the offset.
> 
> Therefore, we have to add code to the 24 bit accessor functions
> that adjusts the register number for these exended registers.
> 
> The formula finally used was developed and proposed by
> Andy Shevchenko <andy.shevchenko@...il.com>.
> 
> Suggested-by: Andy Shevchenko <andy.shevchenko@...il.com>
> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
> ---
>  drivers/gpio/gpio-pca953x.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
> index c682921d7019..4ad553f4e41f 100644
> --- a/drivers/gpio/gpio-pca953x.c
> +++ b/drivers/gpio/gpio-pca953x.c
> @@ -222,9 +222,11 @@ static int pca957x_write_regs_16(struct pca953x_chip *chip, int reg, u8 *val)
>  static int pca953x_write_regs_24(struct pca953x_chip *chip, int reg, u8 *val)
>  {
>  	int bank_shift = fls((chip->gpio_chip.ngpio - 1) / BANK_SZ);
> +	int addr = (reg & PCAL_GPIO_MASK) << bank_shift;
> +	int pinctrl = (reg & PCAL_PINCTRL_MASK) << 1;

Is this reasonable to do on each register access? Compiler will not be
able to optimize out fls and shifts, right?

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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