Re: [PATCH v4 2/5] clk: qcom: regmap: add pipe clk implementation

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Sun, May 01, 2022 at 10:21:46PM +0300, Dmitry Baryshkov wrote:
> On recent Qualcomm platforms the QMP PIPE clocks feed into a set of
> muxes which must be parked to the "safe" source (bi_tcxo) when
> corresponding GDSC is turned off and on again. Currently this is
> handcoded in the PCIe driver by reparenting the gcc_pipe_N_clk_src
> clock. However the same code sequence should be applied in the
> pcie-qcom endpoint, USB3 and UFS drivers.
> 
> Rather than copying this sequence over and over again, follow the
> example of clk_rcg2_shared_ops and implement this parking in the
> enable() and disable() clock operations. Suppliement the regmap-mux with
> the new regmap-pipe implementation, which hides multiplexer behind
> simple branch-like clock. This is possible since each of this
> multiplexers has just two clock sources: working (pipe) and safe
> (bi_tcxo) clock sources. If the clock is running off the external pipe
> source, report it as enable and report it as disabled otherwise.
> 

Sorry for chiming in late and providing comments that might have been addressed
before. But I have few questions below:

> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
>  drivers/clk/qcom/Makefile          |  1 +
>  drivers/clk/qcom/clk-regmap-pipe.c | 62 ++++++++++++++++++++++++++++++
>  drivers/clk/qcom/clk-regmap-pipe.h | 24 ++++++++++++
>  3 files changed, 87 insertions(+)
>  create mode 100644 drivers/clk/qcom/clk-regmap-pipe.c
>  create mode 100644 drivers/clk/qcom/clk-regmap-pipe.h
> 
> diff --git a/drivers/clk/qcom/Makefile b/drivers/clk/qcom/Makefile
> index 671cf5821af1..882c8ecc2e93 100644
> --- a/drivers/clk/qcom/Makefile
> +++ b/drivers/clk/qcom/Makefile
> @@ -11,6 +11,7 @@ clk-qcom-y += clk-branch.o
>  clk-qcom-y += clk-regmap-divider.o
>  clk-qcom-y += clk-regmap-mux.o
>  clk-qcom-y += clk-regmap-mux-div.o
> +clk-qcom-y += clk-regmap-pipe.o
>  clk-qcom-$(CONFIG_KRAIT_CLOCKS) += clk-krait.o
>  clk-qcom-y += clk-hfpll.o
>  clk-qcom-y += reset.o
> diff --git a/drivers/clk/qcom/clk-regmap-pipe.c b/drivers/clk/qcom/clk-regmap-pipe.c
> new file mode 100644
> index 000000000000..9a7c27cc644b
> --- /dev/null
> +++ b/drivers/clk/qcom/clk-regmap-pipe.c
> @@ -0,0 +1,62 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022, Linaro Ltd.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/bitops.h>
> +#include <linux/regmap.h>
> +#include <linux/export.h>
> +
> +#include "clk-regmap-pipe.h"
> +
> +static inline struct clk_regmap_pipe *to_clk_regmap_pipe(struct clk_hw *hw)
> +{
> +	return container_of(to_clk_regmap(hw), struct clk_regmap_pipe, clkr);
> +}
> +
> +static int pipe_is_enabled(struct clk_hw *hw)
> +{
> +	struct clk_regmap_pipe *pipe = to_clk_regmap_pipe(hw);
> +	struct clk_regmap *clkr = to_clk_regmap(hw);
> +	unsigned int mask = GENMASK(pipe->width + pipe->shift - 1, pipe->shift);
> +	unsigned int val;
> +
> +	regmap_read(clkr->regmap, pipe->reg, &val);
> +	val = (val & mask) >> pipe->shift;
> +
> +	WARN_ON(unlikely(val != pipe->enable_val && val != pipe->disable_val));
> +
> +	return val == pipe->enable_val;

Selecting the clk parents in the enable/disable callback seems fine to me but
the way it is implemented doesn't look right.

First this "pipe_clksrc" is a mux clk by design, since we can only select the
parent. But you are converting it to a gate clk now.

Instead of that, my proposal would be to make this clk a composite one i.e,.
gate clk + mux clk. So even though the gate clk here would be a hack, we are
not changing the definition of mux clk.

So you can introduce a new ops like "clk_regmap_mux_gate_ops" and implement the
parent switching logic in the enable/disable callbacks. Additional benefit of
this ops is, in the future we can also support "gate + mux" clks easily.

Also, please don't use the "enable_val/disable_val" members. It should be
something like "mux_sel_pre/mux_sel_post".

> +}
> +
> +static int pipe_enable(struct clk_hw *hw)
> +{
> +	struct clk_regmap_pipe *pipe = to_clk_regmap_pipe(hw);
> +	struct clk_regmap *clkr = to_clk_regmap(hw);
> +	unsigned int mask = GENMASK(pipe->width + pipe->shift - 1, pipe->shift);
> +	unsigned int val;
> +
> +	val = pipe->enable_val << pipe->shift;
> +
> +	return regmap_update_bits(clkr->regmap, pipe->reg, mask, val);
> +}
> +
> +static void pipe_disable(struct clk_hw *hw)
> +{
> +	struct clk_regmap_pipe *pipe = to_clk_regmap_pipe(hw);
> +	struct clk_regmap *clkr = to_clk_regmap(hw);
> +	unsigned int mask = GENMASK(pipe->width + pipe->shift - 1, pipe->shift);
> +	unsigned int val;
> +
> +	val = pipe->disable_val << pipe->shift;
> +
> +	regmap_update_bits(clkr->regmap, pipe->reg, mask, val);
> +}
> +
> +const struct clk_ops clk_regmap_pipe_ops = {
> +	.enable = pipe_enable,
> +	.disable = pipe_disable,
> +	.is_enabled = pipe_is_enabled,
> +};
> +EXPORT_SYMBOL_GPL(clk_regmap_pipe_ops);
> diff --git a/drivers/clk/qcom/clk-regmap-pipe.h b/drivers/clk/qcom/clk-regmap-pipe.h
> new file mode 100644
> index 000000000000..cfaa792a029b
> --- /dev/null
> +++ b/drivers/clk/qcom/clk-regmap-pipe.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2022, Linaru Ltd.

Linaro

> + * Author: Dmitry Baryshkov

No email?

Thanks,
Mani

> + */
> +
> +#ifndef __QCOM_CLK_REGMAP_PIPE_H__
> +#define __QCOM_CLK_REGMAP_PIPE_H__
> +
> +#include <linux/clk-provider.h>
> +#include "clk-regmap.h"
> +
> +struct clk_regmap_pipe {
> +	u32			reg;
> +	u32			shift;
> +	u32			width;
> +	u32			enable_val;
> +	u32			disable_val;
> +	struct clk_regmap	clkr;
> +};
> +
> +extern const struct clk_ops clk_regmap_pipe_ops;
> +
> +#endif
> -- 
> 2.35.1
>