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

Light Hsieh
2020-08-21T10:51:01Z

On Fri, 2020-08-21 at 02:59 -0700, Sean Wang wrote:
> Hi Light,
>
> On Thu, Aug 20, 2020 at 9:47 PM Light Hsieh <light.hsieh@mediatek.com> wrote:
> >
> > On Wed, 2020-08-19 at 16:11 -0700, Sean Wang wrote:
> > > Hi Light,
> > >
> > > On Tue, Aug 18, 2020 at 1:36 AM <light.hsieh@mediatek.com> wrote:
> > > >
> > > > From: Light Hsieh <light.hsieh@mediatek.com>
> > > >
> > > > 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@mediatek.com>
> > > > ---
> > > > 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/
> >
> > Not only MT6765 provides such control registers.
> > Actually, many (but not all) MediaTek SoC support.
> > Other MediaTek SoC can enable such control according to its HW support.
> >
> > >
> > > > + * 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?
> >
> > Yes. However, use set/clr to change mode require 2 register access when
> > target mode is not all 0's or all 1's.
>
> DRV/TDSEL and RDSEL register might have value not all 0's or all 1's.
> That seems to be we still require two steps register access for such
> fields, right?

Yes.

>
> > The mwr HW support is not available on mode register.
>
> if I understand correctly, that seems to be a typo, MWR should be only
> available on mode register
>

Sorry, it's my typo.

> >
> > >
> > > > +#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
> > >
> >
> > pf->mask cannot be used direct. It needs conversion.For example:
> > pf->mask: 0x1f -> value_new = (1 << 4) | value;
> > pf->mask: 0xf -> value_new = (1 << 3) | value;
> > pf->mask: 0x7 -> value_new = (1 << 2) | value;
> >
> > The code size of perform conversion is greater than using a direct
> > mwr_field_width field.
> >
>
> using pf->mask can allow MWR supports any field that can support MWR
> to be generic.
>
> that would be a mess when there are more fields relying on MWR on
> certain SoC someday.
>
The most important reason for MWR on mode register is that:
2 access will create an un-wanted temp mode in that GPIO pin and
un-expected signal may be produced.

Currently, we don't see the need to support MWR on other field since MWR
support is added for mode register at 2014. Therefore, the future usage
consideration may be never used.

> >
> > > > + 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(...);
> > > }
> > >
> >
> > Sine there is no member 'field' in struct mtk_pin_field, pf->field
> > cannot be used.
> > Therefore an extra function parameter is required if you want to use a
> > standalone function mtk_hw_rmw. Like this:
> >
> > void mtk_hw_rmw(struct mtk_pinctrl *pctl, struct mtk_pin_field *pf,
> > int field, u32 value)
> > {
> > 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);
> > }
> >
> > I wonder the necessity/efficiency of such extra intermediate function
> > with many function parameters.
>
> holding it in a separate function is for that operation is not generic
> enough for the moment.
>
> >
> >
> > > > + 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