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SubjectRe: [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@gmail.com>.
>
> Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.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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