linux-kernel - Re: [PATCH] pinctrl: meson: fix drive strength register and bit calculation

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Message-ID: <1jo8prnk2x.fsf@starbuckisacylon.baylibre.com>
Date:   Wed, 10 Jun 2020 15:09:42 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     hhk7734@...il.com, linus.walleij@...aro.org, khilman@...libre.com
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH] pinctrl: meson: fix drive strength register and bit calculation


On Wed 10 Jun 2020 at 06:13, hhk7734@...il.com wrote:

> From: Hyeonki Hong <hhk7734@...il.com>
>
> If a GPIO bank has greater than 16 pins, PAD_DS_REG is split into two
> registers. However, when register and bit were calculated, the first
> register defined in the bank was used, and the bit was calculated based
> on the first pin. This causes problems in setting the driving strength.
>
> Solved the problem by changing the bit using a mask and selecting the
> next register when the bit exceeds 15.

This fixes the case of GPIOX on g12 which goes up to 18 yes but the same
problem will happen again a if bank ever goes past 31 pins. In such case
the problem would apply to all reg types.

I would prefer if it was solved in a more generic fashion, like defining
a "stride" table with the values of each reg type. This table can common
to all aml SoCs for now but eventually it probably need to be SoC
specific.

This would allow to :
A) handle the case you are reporting in a generic (future proof) way
B) remove the weird "bit = bit << 1;" calc in place in the get/set of
the drive strengh pinconf

>
> Signed-off-by: Hyeonki Hong <hhk7734@...il.com>
> ---
>  drivers/pinctrl/meson/pinctrl-meson.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/pinctrl/meson/pinctrl-meson.c b/drivers/pinctrl/meson/pinctrl-meson.c
> index bbc919bef2bf..ef66239b7df5 100644
> --- a/drivers/pinctrl/meson/pinctrl-meson.c
> +++ b/drivers/pinctrl/meson/pinctrl-meson.c
> @@ -98,6 +98,13 @@ static void meson_calc_reg_and_bit(struct meson_bank *bank, unsigned int pin,
>
>  	*reg = desc->reg * 4;
>  	*bit = desc->bit + pin - bank->first;
> +
> +	if (reg_type == REG_DS) {
> +		if (*bit > 15) {
> +			*bit &= 0xf;
> +			*reg += 4;
> +		}
> +	}
>  }
>
>  static int meson_get_groups_count(struct pinctrl_dev *pcdev)