Re: [PATCH RESEND 3/7] clk: spacemit: add reset controller support

[Alex Elder]

On 3/24/25 7:20 AM, Haylen Chu wrote:
> On Fri, Mar 21, 2025 at 10:18:26AM -0500, Alex Elder wrote:
> > Define ccu_reset_data as a structure that contains the constant
> > register offset and bitmasks used to assert and deassert a reset
> > control on a SpacemiT K1 CCU. Define ccu_reset_controller_data as
> > a structure that contains the address of an array of those structures
> > and a count of the number of elements in the array.
> >
> > Add a pointer to a ccu_reset_controller_data structure to the
> > k1_ccu_data structure.  Reset support is optional for SpacemiT CCUs;
> > the new pointer field will be null for CCUs without any resets.
> >
> > Finally, define a new ccu_reset_controller structure, which (for
> > a CCU with resets) contains a pointer to the constant reset data,
> > the regmap to be used for the controller, and an embedded a reset
> > controller structure.
> >
> > Each reset control is asserted or deasserted by updating bits in
> > a register.  The bits used are defined by an assert mask and a
> > deassert mask.  In some cases, one (non-zero) mask asserts reset
> > and a different (non-zero) mask deasserts it.  Otherwise one mask
> > is nonzero, and the other is zero.  Either way, the bits in
> > both masks are cleared, then either the assert mask or the deassert
> > mask is set in a register to affect the state of a reset control.
> >
> > Signed-off-by: Alex Elder <elder@xxxxxxxxxxxx>
> > ---
> >   drivers/clk/spacemit/ccu-k1.c | 93 +++++++++++++++++++++++++++++++++++
> >   1 file changed, 93 insertions(+)
> >
> > diff --git a/drivers/clk/spacemit/ccu-k1.c b/drivers/clk/spacemit/ccu-k1.c
> > index f7367271396a0..6d879411c6c05 100644
> > --- a/drivers/clk/spacemit/ccu-k1.c
> > +++ b/drivers/clk/spacemit/ccu-k1.c
>
> ...
>
> > +static int
> > +k1_rst_update(struct reset_controller_dev *rcdev, unsigned long id, bool assert)
> > +{
> > +	struct ccu_reset_controller *controller = rcdev_to_controller(rcdev);
> > +	struct regmap *regmap = controller->regmap;
> > +	const struct ccu_reset_data *data;
> > +	u32 val;
> > +	int ret;
> > +
> > +	data = &controller->data->data[id];
> > +
> > +	ret = regmap_read(regmap, data->offset, &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	val &= ~(data->assert_mask | data->deassert_mask);
> > +	val |= assert ? data->assert_mask : data->deassert_mask;
> > +
> > +	return regmap_write(regmap, data->offset, val);
> > +}
>
> I don't think it's safe to write the regmap based on a value read
> earlier without the regmap's inner lock held: it's totally fine for the
> clock part to issue an update of the register at the same time. Without
> knowledge on it, reset code may rollback the clock bits written by clock
> code earlier to the original value. That's why I keep using ccu_update()
> everywhere and dropped ccu_write().

That's a great point, thank you.  I'll modify it to use
regmap_update_bits(), which is better anyway.

					-Alex

> Thanks,
> Haylen Chu