Re: [PATCH v1 1/2] pinctrl: mediatek: support access registers without race-condition

From: Sean Wang
Date: Wed Aug 19 2020 - 19:11:53 EST

Hi Light,

On Tue, Aug 18, 2020 at 1:36 AM <light.hsieh@xxxxxxxxxxxx> wrote:
>
> From: Light Hsieh <light.hsieh@xxxxxxxxxxxx>
>
> Some MediaTek SOC provide more control registers other than value register.

s/MT6765/Some MediaTek SoC/

> Generanll, a value register need read-modify-write is at offset 0xXXXXXXXX0.

s/Generally/Generanll/

> A corresponding SET register is at offset 0xXXXXXXX4. Write 1s' to some bits
> of SET register will set same bits in value register.
> A corresponding CLR register is at offset 0xXXXXXXX8. Write 1s' to some bits
> of CLR register will clear same bits in value register.
> For GPIO mode selection, MWR register is provided at offset 0xXXXXXXXC.
> With MWR, the MSBit of GPIO mode selection field is for modification-enable,
> not for GPIO mode selection, and the remaining LSBits are for mode
> selection.
> Take mode selection field with 4-bits as example, to select mode 0~7 via
> MWR register, 8~15 (instead of 0~7) shall be written to corresponding mode
> selection field.
> When using SET/CLR/MWR registers, read-modify-write of value register is not
> necessary. This can prevent from race condition when multiple bus masters
> concurrently read-modify-write the same value register for setting different
> fields of the same value register.
>
> Signed-off-by: Light Hsieh <light.hsieh@xxxxxxxxxxxx>
> ---
> drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c | 69 ++++++++++++++++++++++--
> drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.h | 2 +
> 2 files changed, 67 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c b/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c
> index b77b18f..51f0b53 100644
> --- a/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c
> +++ b/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.c
> @@ -18,6 +18,29 @@
> #include "mtk-eint.h"
> #include "pinctrl-mtk-common-v2.h"
>
> +/* Some MediaTek SOC provide more control registers other than value register.

s/MT6765/Some MediaTek SoC/

> + * Generanll, a value register need read-modify-write is at offset 0xXXXXXXXX0.

s/Generally/Generanll/

> + * A corresponding SET register is at offset 0xXXXXXXX4. Write 1s' to some bits
> + * of SET register will set same bits in value register.
> + * A corresponding CLR register is at offset 0xXXXXXXX8. Write 1s' to some bits
> + * of CLR register will clear same bits in value register.
> + * For GPIO mode selection, MWR register is provided at offset 0xXXXXXXXC.
> + * With MWR, the MSBit of GPIO mode selection field is for modification-enable,
> + * not for GPIO mode selection, and the remaining LSBits are for mode
> + * selection.
> + * Take mode selection field with 4-bits as example, to select mode 0~7 via
> + * MWR register, 8~15 (instead of 0~7) shall be written to corresponding mode
> + * selection field.
> + * When using SET/CLR/MWR registers, read-modify-write of value register is not
> + * necessary. This can prevent from race condition when multiple bus masters
> + * concurrently read-modify-write the same value register for setting different
> + * fields of the same value register.
> + */
> +
> +#define SET_OFFSET 0x4
> +#define CLR_OFFSET 0x8

can set/clr offset work for mode register?

> +#define MWR_OFFSET 0xC
> +
> /**
> * struct mtk_drive_desc - the structure that holds the information
> * of the driving current
> @@ -64,6 +87,38 @@ void mtk_rmw(struct mtk_pinctrl *pctl, u8 i, u32 reg, u32 mask, u32 set)
> mtk_w32(pctl, i, reg, val);
> }
>
> +
> +static void mtk_hw_set_value_race_free(struct mtk_pinctrl *pctl,
> + struct mtk_pin_field *pf, u32 value)

s/mtk_hw_set_value_race_free/mtk_hw_w1sc/ to explictly indicate
write-one ethier set or clear operation supported by hw

> +{
> + unsigned int set, clr;
> +
> + set = value & pf->mask;
> + clr = (~set) & pf->mask;
> +
> + if (set)
> + mtk_w32(pctl, pf->index, pf->offset + SET_OFFSET,
> + set << pf->bitpos);
> + if (clr)
> + mtk_w32(pctl, pf->index, pf->offset + CLR_OFFSET,
> + clr << pf->bitpos);
> +}
> +
> +static void mtk_hw_set_mode_race_free(struct mtk_pinctrl *pctl,
> + struct mtk_pin_field *pf, u32 value)

s/mtk_hw_set_mode_race_free/mtk_hw_mwr/

> +{
> + unsigned int value_new;
> +
> + /* MSB of mask is modification-enable bit, set this bit */
> + value_new = (1 << (pctl->soc->mwr_field_width - 1)) | value;

it seems to be we can use fls(pf->mask) to replace ctl->soc->mwr_field_width

> + if (value_new == value)
> + dev_notice(pctl->dev,
> + "invalid mode 0x%x, use it by ignoring MSBit!\n",
> + value);
> + mtk_w32(pctl, pf->index, pf->offset + MWR_OFFSET,
> + value_new << pf->bitpos);
> +}
> +
> static int mtk_hw_pin_field_lookup(struct mtk_pinctrl *hw,
> const struct mtk_pin_desc *desc,
> int field, struct mtk_pin_field *pfd)
> @@ -197,10 +252,16 @@ int mtk_hw_set_value(struct mtk_pinctrl *hw, const struct mtk_pin_desc *desc,
> if (value < 0 || value > pf.mask)
> return -EINVAL;
>
> - if (!pf.next)
> - mtk_rmw(hw, pf.index, pf.offset, pf.mask << pf.bitpos,
> - (value & pf.mask) << pf.bitpos);
> - else
> + if (!pf.next) {
> + if (hw->soc->race_free_access) {

let's create an extra flags caps under hw->soc and the SoC capability
check, something like hw->soc->caps & MTK_HW_CAPS_RMW_ATOMIC to easily
extend various things for future SoC

> + if (field == PINCTRL_PIN_REG_MODE)
> + mtk_hw_set_mode_race_free(hw, &pf, value);
> + else
> + mtk_hw_set_value_race_free(hw, &pf, value);
> + }

let's create a function holding that specific hardware stuff (at least
currently it look like), something like

static void mtk_hw_rmw(struct mtk_pinctrl *pctl, struct mtk_pin_field *pf)
{
if (pf->field == PINCTRL_PIN_REG_MODE) /* create a member field for pf */
mtk_hw_mwr(...);
else
mtk_hw_w1sc(...);
}

> + mtk_rmw(hw, pf.index, pf.offset, pf.mask << pf.bitpos,
> + (value & pf.mask) << pf.bitpos);
> + } else
> mtk_hw_write_cross_field(hw, &pf, value);
>
> return 0;
> diff --git a/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.h b/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.h
> index 27df087..95fb329 100644
> --- a/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.h
> +++ b/drivers/pinctrl/mediatek/pinctrl-mtk-common-v2.h
> @@ -203,6 +203,8 @@ struct mtk_pin_soc {
> /* Specific parameters per SoC */
> u8 gpio_m;
> bool ies_present;
> + bool race_free_access;
> + unsigned int mwr_field_width;
> const char * const *base_names;
> unsigned int nbase_names;
>
> --
> 1.8.1.1.dirty