[PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Cristian Marussi]

Support also atomic enable/disable clk_ops beside the bare non-atomic one
(prepare/unprepare) when the underlying SCMI transport is configured to
support atomic transactions for synchronous commands.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-clk@vger.kernel.org
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
V5 --> V6
- add concurrent availability of atomic and non atomic reqs
---
 drivers/clk/clk-scmi.c | 56 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 47 insertions(+), 9 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index 1e357d364ca2..50033d873dde 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c
@@ -88,21 +88,53 @@ static void scmi_clk_disable(struct clk_hw *hw)
 	scmi_proto_clk_ops->disable(clk->ph, clk->id);
 }
 
+static int scmi_clk_atomic_enable(struct clk_hw *hw)
+{
+	struct scmi_clk *clk = to_scmi_clk(hw);
+
+	return scmi_proto_clk_ops->enable_atomic(clk->ph, clk->id);
+}
+
+static void scmi_clk_atomic_disable(struct clk_hw *hw)
+{
+	struct scmi_clk *clk = to_scmi_clk(hw);
+
+	scmi_proto_clk_ops->disable_atomic(clk->ph, clk->id);
+}
+
+/*
+ * We can provide enable/disable atomic callbacks only if the underlying SCMI
+ * transport for an SCMI instance is configured to handle SCMI commands in an
+ * atomic manner.
+ *
+ * When no SCMI atomic transport support is available we instead provide only
+ * the prepare/unprepare API, as allowed by the clock framework when atomic
+ * calls are not available.
+ *
+ * Two distinct sets of clk_ops are provided since we could have multiple SCMI
+ * instances with different underlying transport quality, so they cannot be
+ * shared.
+ */
 static const struct clk_ops scmi_clk_ops = {
 	.recalc_rate = scmi_clk_recalc_rate,
 	.round_rate = scmi_clk_round_rate,
 	.set_rate = scmi_clk_set_rate,
-	/*
-	 * We can't provide enable/disable callback as we can't perform the same
-	 * in atomic context. Since the clock framework provides standard API
-	 * clk_prepare_enable that helps cases using clk_enable in non-atomic
-	 * context, it should be fine providing prepare/unprepare.
-	 */
 	.prepare = scmi_clk_enable,
 	.unprepare = scmi_clk_disable,
 };
 
-static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
+static const struct clk_ops scmi_atomic_clk_ops = {
+	.recalc_rate = scmi_clk_recalc_rate,
+	.round_rate = scmi_clk_round_rate,
+	.set_rate = scmi_clk_set_rate,
+	.prepare = scmi_clk_enable,
+	.unprepare = scmi_clk_disable,
+	.enable = scmi_clk_atomic_enable,
+	.disable = scmi_clk_atomic_disable,
+};
+
+static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk,
+			     const struct clk_ops *scmi_ops)
 {
 	int ret;
 	unsigned long min_rate, max_rate;
@@ -110,7 +142,7 @@ static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
 	struct clk_init_data init = {
 		.flags = CLK_GET_RATE_NOCACHE,
 		.num_parents = 0,
-		.ops = &scmi_clk_ops,
+		.ops = scmi_ops,
 		.name = sclk->info->name,
 	};
 
@@ -145,6 +177,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 	struct device_node *np = dev->of_node;
 	const struct scmi_handle *handle = sdev->handle;
 	struct scmi_protocol_handle *ph;
+	const struct clk_ops *scmi_ops;
 
 	if (!handle)
 		return -ENODEV;
@@ -168,6 +201,11 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 	clk_data->num = count;
 	hws = clk_data->hws;
 
+	if (handle->is_transport_atomic(handle))
+		scmi_ops = &scmi_atomic_clk_ops;
+	else
+		scmi_ops = &scmi_clk_ops;
+
 	for (idx = 0; idx < count; idx++) {
 		struct scmi_clk *sclk;
 
@@ -184,7 +222,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 		sclk->id = idx;
 		sclk->ph = ph;
 
-		err = scmi_clk_ops_init(dev, sclk);
+		err = scmi_clk_ops_init(dev, sclk, scmi_ops);
 		if (err) {
 			dev_err(dev, "failed to register clock %d\n", idx);
 			devm_kfree(dev, sclk);
-- 
2.17.1

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Stephen Boyd]

Quoting Cristian Marussi (2021-11-29 11:11:56)
> Support also atomic enable/disable clk_ops beside the bare non-atomic one
> (prepare/unprepare) when the underlying SCMI transport is configured to
> support atomic transactions for synchronous commands.
> 
> Cc: Michael Turquette <mturquette@baylibre.com>
> Cc: Stephen Boyd <sboyd@kernel.org>
> Cc: linux-clk@vger.kernel.org
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---

Acked-by: Stephen Boyd <sboyd@kernel.org>

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Florian Fainelli]

On 11/29/21 11:11 AM, Cristian Marussi wrote:
> Support also atomic enable/disable clk_ops beside the bare non-atomic one
> (prepare/unprepare) when the underlying SCMI transport is configured to
> support atomic transactions for synchronous commands.
> 
> Cc: Michael Turquette <mturquette@baylibre.com>
> Cc: Stephen Boyd <sboyd@kernel.org>
> Cc: linux-clk@vger.kernel.org
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Vincent Guittot]

Hi Cristian,

On Mon, 29 Nov 2021 at 20:13, Cristian Marussi <cristian.marussi@arm.com> wrote:
>
> Support also atomic enable/disable clk_ops beside the bare non-atomic one
> (prepare/unprepare) when the underlying SCMI transport is configured to
> support atomic transactions for synchronous commands.
>
> Cc: Michael Turquette <mturquette@baylibre.com>
> Cc: Stephen Boyd <sboyd@kernel.org>
> Cc: linux-clk@vger.kernel.org
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
> V5 --> V6
> - add concurrent availability of atomic and non atomic reqs
> ---
>  drivers/clk/clk-scmi.c | 56 +++++++++++++++++++++++++++++++++++-------
>  1 file changed, 47 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
> index 1e357d364ca2..50033d873dde 100644
> --- a/drivers/clk/clk-scmi.c
> +++ b/drivers/clk/clk-scmi.c
> @@ -88,21 +88,53 @@ static void scmi_clk_disable(struct clk_hw *hw)
>         scmi_proto_clk_ops->disable(clk->ph, clk->id);
>  }
>
> +static int scmi_clk_atomic_enable(struct clk_hw *hw)
> +{
> +       struct scmi_clk *clk = to_scmi_clk(hw);
> +
> +       return scmi_proto_clk_ops->enable_atomic(clk->ph, clk->id);
> +}
> +
> +static void scmi_clk_atomic_disable(struct clk_hw *hw)
> +{
> +       struct scmi_clk *clk = to_scmi_clk(hw);
> +
> +       scmi_proto_clk_ops->disable_atomic(clk->ph, clk->id);
> +}
> +
> +/*
> + * We can provide enable/disable atomic callbacks only if the underlying SCMI
> + * transport for an SCMI instance is configured to handle SCMI commands in an
> + * atomic manner.
> + *
> + * When no SCMI atomic transport support is available we instead provide only
> + * the prepare/unprepare API, as allowed by the clock framework when atomic
> + * calls are not available.
> + *
> + * Two distinct sets of clk_ops are provided since we could have multiple SCMI
> + * instances with different underlying transport quality, so they cannot be
> + * shared.
> + */
>  static const struct clk_ops scmi_clk_ops = {
>         .recalc_rate = scmi_clk_recalc_rate,
>         .round_rate = scmi_clk_round_rate,
>         .set_rate = scmi_clk_set_rate,
> -       /*
> -        * We can't provide enable/disable callback as we can't perform the same
> -        * in atomic context. Since the clock framework provides standard API
> -        * clk_prepare_enable that helps cases using clk_enable in non-atomic
> -        * context, it should be fine providing prepare/unprepare.
> -        */
>         .prepare = scmi_clk_enable,
>         .unprepare = scmi_clk_disable,
>  };
>
> -static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
> +static const struct clk_ops scmi_atomic_clk_ops = {
> +       .recalc_rate = scmi_clk_recalc_rate,
> +       .round_rate = scmi_clk_round_rate,
> +       .set_rate = scmi_clk_set_rate,
> +       .prepare = scmi_clk_enable,
> +       .unprepare = scmi_clk_disable,
> +       .enable = scmi_clk_atomic_enable,

For  each clock, we have to start with  clk_prepare and then clk_enable
this means that for scmi clk we will do
scmi_clk_enable
then
scmi_clk_atomic_enable

scmi_clk_enable and scmi_clk_atomic_enable ends up doing the same
thing: scmi_clock_config_set but the atomic version doesn't sleep

So you will set enable twice the clock.

This is confirmed when testing your series with virtio scmi backend as
I can see to consecutive scmi clk set enable request for the same
clock

In case of atomic mode, the clk_prepare should  be a nop

> +       .disable = scmi_clk_atomic_disable,
> +};
> +
> +static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk,
> +                            const struct clk_ops *scmi_ops)
>  {
>         int ret;
>         unsigned long min_rate, max_rate;
> @@ -110,7 +142,7 @@ static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
>         struct clk_init_data init = {
>                 .flags = CLK_GET_RATE_NOCACHE,
>                 .num_parents = 0,
> -               .ops = &scmi_clk_ops,
> +               .ops = scmi_ops,
>                 .name = sclk->info->name,
>         };
>
> @@ -145,6 +177,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
>         struct device_node *np = dev->of_node;
>         const struct scmi_handle *handle = sdev->handle;
>         struct scmi_protocol_handle *ph;
> +       const struct clk_ops *scmi_ops;
>
>         if (!handle)
>                 return -ENODEV;
> @@ -168,6 +201,11 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
>         clk_data->num = count;
>         hws = clk_data->hws;
>
> +       if (handle->is_transport_atomic(handle))
> +               scmi_ops = &scmi_atomic_clk_ops;
> +       else
> +               scmi_ops = &scmi_clk_ops;
> +
>         for (idx = 0; idx < count; idx++) {
>                 struct scmi_clk *sclk;
>
> @@ -184,7 +222,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
>                 sclk->id = idx;
>                 sclk->ph = ph;
>
> -               err = scmi_clk_ops_init(dev, sclk);
> +               err = scmi_clk_ops_init(dev, sclk, scmi_ops);
>                 if (err) {
>                         dev_err(dev, "failed to register clock %d\n", idx);
>                         devm_kfree(dev, sclk);
> --
> 2.17.1
>

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Cristian Marussi]

On Fri, Dec 10, 2021 at 11:52:39AM +0100, Vincent Guittot wrote:
> Hi Cristian,
> 

Hi Vincent,

thanks for the feedback, my replies below.

> On Mon, 29 Nov 2021 at 20:13, Cristian Marussi <cristian.marussi@arm.com> wrote:
> >
> > Support also atomic enable/disable clk_ops beside the bare non-atomic one
> > (prepare/unprepare) when the underlying SCMI transport is configured to
> > support atomic transactions for synchronous commands.
> >
> > Cc: Michael Turquette <mturquette@baylibre.com>
> > Cc: Stephen Boyd <sboyd@kernel.org>
> > Cc: linux-clk@vger.kernel.org
> > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> > ---
> > V5 --> V6
> > - add concurrent availability of atomic and non atomic reqs
> > ---
> >  drivers/clk/clk-scmi.c | 56 +++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 47 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
> > index 1e357d364ca2..50033d873dde 100644
> > --- a/drivers/clk/clk-scmi.c
> > +++ b/drivers/clk/clk-scmi.c
> > @@ -88,21 +88,53 @@ static void scmi_clk_disable(struct clk_hw *hw)
> >         scmi_proto_clk_ops->disable(clk->ph, clk->id);
> >  }
> >
> > +static int scmi_clk_atomic_enable(struct clk_hw *hw)
> > +{
> > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > +
> > +       return scmi_proto_clk_ops->enable_atomic(clk->ph, clk->id);
> > +}
> > +
> > +static void scmi_clk_atomic_disable(struct clk_hw *hw)
> > +{
> > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > +
> > +       scmi_proto_clk_ops->disable_atomic(clk->ph, clk->id);
> > +}
> > +
> > +/*
> > + * We can provide enable/disable atomic callbacks only if the underlying SCMI
> > + * transport for an SCMI instance is configured to handle SCMI commands in an
> > + * atomic manner.
> > + *
> > + * When no SCMI atomic transport support is available we instead provide only
> > + * the prepare/unprepare API, as allowed by the clock framework when atomic
> > + * calls are not available.
> > + *
> > + * Two distinct sets of clk_ops are provided since we could have multiple SCMI
> > + * instances with different underlying transport quality, so they cannot be
> > + * shared.
> > + */
> >  static const struct clk_ops scmi_clk_ops = {
> >         .recalc_rate = scmi_clk_recalc_rate,
> >         .round_rate = scmi_clk_round_rate,
> >         .set_rate = scmi_clk_set_rate,
> > -       /*
> > -        * We can't provide enable/disable callback as we can't perform the same
> > -        * in atomic context. Since the clock framework provides standard API
> > -        * clk_prepare_enable that helps cases using clk_enable in non-atomic
> > -        * context, it should be fine providing prepare/unprepare.
> > -        */
> >         .prepare = scmi_clk_enable,
> >         .unprepare = scmi_clk_disable,
> >  };
> >
> > -static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
> > +static const struct clk_ops scmi_atomic_clk_ops = {
> > +       .recalc_rate = scmi_clk_recalc_rate,
> > +       .round_rate = scmi_clk_round_rate,
> > +       .set_rate = scmi_clk_set_rate,
> > +       .prepare = scmi_clk_enable,
> > +       .unprepare = scmi_clk_disable,
> > +       .enable = scmi_clk_atomic_enable,
> 
> For  each clock, we have to start with  clk_prepare and then clk_enable
> this means that for scmi clk we will do
> scmi_clk_enable
> then
> scmi_clk_atomic_enable
> 
> scmi_clk_enable and scmi_clk_atomic_enable ends up doing the same
> thing: scmi_clock_config_set but the atomic version doesn't sleep
> 
> So you will set enable twice the clock.
> 
> This is confirmed when testing your series with virtio scmi backend as
> I can see to consecutive scmi clk set enable request for the same
> clock
> 

Yes, I saw that double enable while testing with CLK debugfs entry BUT I
thought that was due to the design of the debugfs entries (that calls
prepare_enable and so prepare and enable in sequence) also becauase, a few
versions ago, this series WAS indeed providing (beside bugs :P) the
sleeping prepare XOR the atomic enable depending on the SCMI atomic support
state (as you are suggesting now), BUT, after a few offline chats with you,
my (probably faulty) understanding was that some partners, even on a system
supporting atomic SCMI transfers, would have liked to be able to call the
atomic .enable selectively only on some (tipically quickly to setup) clocks
while keep calling the sleeping .prepare on some other (slower ones to
settle). (while keeping all the other slower clk_rate setup ops non-atomic)

So in v6/v7 I changed the API to provide both sleepable and atomic clk APIs
when the underlying SCMI stack support atomic mode: this way, though, it is
clearly up to the caller to decide what to do and if, generally, the
clock framework just calls everytime both, it will result in a double
enable.

Was my understanding of the reqs about being able to selectively choose
the sleep_vs_atomic mode in this way wrong ?

> In case of atomic mode, the clk_prepare should  be a nop
> 

I can certainly revert to use the old exclusive approach, not providing
a .prepare when atomic is supported, but then all clock enable ops on any
clock defined on the system will be operated atomically withot any choice
when atomic SCMI transactions are available.

Ideally, we could like, on a SCMI system supporting atomic, to be able to
'tag' a specific clock something like 'prefer-non-atomic' and so selectively
'noppify' the .prepare or the .enable at the SCMI clk-driver level depending
on such tag, but I cannot see any way to expose this from the CLK framework
API or DT, nor it seems suitable for a per-clock DT config option AND it
would break the current logic of clk_is_enabled_when_prepared().

Indeed clk_is_enabled_when_prepared() logic is ALREADY broken also by this V7
since when providing also .enable/.disable on atomic transports, the core CLK
framework would return clk_is_enabled_when_prepared() --> False which does
NOT fit reality since our SCMI prepare/unprepare DO enable/disable clks even
if .disable/.enable are provided too.

Probably this last observation on clk_is_enabled_when_prepared() is enough
to revert to the exclusive atomic/non-atomic approach and just ignore the
customer wish to be able to selectively choose which clock to operate in
atomic mode.

Any thoughs before a V8 ?

Thanks,
Cristian
 

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Vincent Guittot]

On Fri, 10 Dec 2021 at 14:30, Cristian Marussi <cristian.marussi@arm.com> wrote:
>
> On Fri, Dec 10, 2021 at 11:52:39AM +0100, Vincent Guittot wrote:
> > Hi Cristian,
> >
>
> Hi Vincent,
>
> thanks for the feedback, my replies below.
>
> > On Mon, 29 Nov 2021 at 20:13, Cristian Marussi <cristian.marussi@arm.com> wrote:
> > >
> > > Support also atomic enable/disable clk_ops beside the bare non-atomic one
> > > (prepare/unprepare) when the underlying SCMI transport is configured to
> > > support atomic transactions for synchronous commands.
> > >
> > > Cc: Michael Turquette <mturquette@baylibre.com>
> > > Cc: Stephen Boyd <sboyd@kernel.org>
> > > Cc: linux-clk@vger.kernel.org
> > > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> > > ---
> > > V5 --> V6
> > > - add concurrent availability of atomic and non atomic reqs
> > > ---
> > >  drivers/clk/clk-scmi.c | 56 +++++++++++++++++++++++++++++++++++-------
> > >  1 file changed, 47 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
> > > index 1e357d364ca2..50033d873dde 100644
> > > --- a/drivers/clk/clk-scmi.c
> > > +++ b/drivers/clk/clk-scmi.c
> > > @@ -88,21 +88,53 @@ static void scmi_clk_disable(struct clk_hw *hw)
> > >         scmi_proto_clk_ops->disable(clk->ph, clk->id);
> > >  }
> > >
> > > +static int scmi_clk_atomic_enable(struct clk_hw *hw)
> > > +{
> > > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > > +
> > > +       return scmi_proto_clk_ops->enable_atomic(clk->ph, clk->id);
> > > +}
> > > +
> > > +static void scmi_clk_atomic_disable(struct clk_hw *hw)
> > > +{
> > > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > > +
> > > +       scmi_proto_clk_ops->disable_atomic(clk->ph, clk->id);
> > > +}
> > > +
> > > +/*
> > > + * We can provide enable/disable atomic callbacks only if the underlying SCMI
> > > + * transport for an SCMI instance is configured to handle SCMI commands in an
> > > + * atomic manner.
> > > + *
> > > + * When no SCMI atomic transport support is available we instead provide only
> > > + * the prepare/unprepare API, as allowed by the clock framework when atomic
> > > + * calls are not available.
> > > + *
> > > + * Two distinct sets of clk_ops are provided since we could have multiple SCMI
> > > + * instances with different underlying transport quality, so they cannot be
> > > + * shared.
> > > + */
> > >  static const struct clk_ops scmi_clk_ops = {
> > >         .recalc_rate = scmi_clk_recalc_rate,
> > >         .round_rate = scmi_clk_round_rate,
> > >         .set_rate = scmi_clk_set_rate,
> > > -       /*
> > > -        * We can't provide enable/disable callback as we can't perform the same
> > > -        * in atomic context. Since the clock framework provides standard API
> > > -        * clk_prepare_enable that helps cases using clk_enable in non-atomic
> > > -        * context, it should be fine providing prepare/unprepare.
> > > -        */
> > >         .prepare = scmi_clk_enable,
> > >         .unprepare = scmi_clk_disable,
> > >  };
> > >
> > > -static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
> > > +static const struct clk_ops scmi_atomic_clk_ops = {
> > > +       .recalc_rate = scmi_clk_recalc_rate,
> > > +       .round_rate = scmi_clk_round_rate,
> > > +       .set_rate = scmi_clk_set_rate,
> > > +       .prepare = scmi_clk_enable,
> > > +       .unprepare = scmi_clk_disable,
> > > +       .enable = scmi_clk_atomic_enable,
> >
> > For  each clock, we have to start with  clk_prepare and then clk_enable
> > this means that for scmi clk we will do
> > scmi_clk_enable
> > then
> > scmi_clk_atomic_enable
> >
> > scmi_clk_enable and scmi_clk_atomic_enable ends up doing the same
> > thing: scmi_clock_config_set but the atomic version doesn't sleep
> >
> > So you will set enable twice the clock.
> >
> > This is confirmed when testing your series with virtio scmi backend as
> > I can see to consecutive scmi clk set enable request for the same
> > clock
> >
>
> Yes, I saw that double enable while testing with CLK debugfs entry BUT I
> thought that was due to the design of the debugfs entries (that calls
> prepare_enable and so prepare and enable in sequence) also becauase, a few
> versions ago, this series WAS indeed providing (beside bugs :P) the
> sleeping prepare XOR the atomic enable depending on the SCMI atomic support
> state (as you are suggesting now), BUT, after a few offline chats with you,
> my (probably faulty) understanding was that some partners, even on a system
> supporting atomic SCMI transfers, would have liked to be able to call the
> atomic .enable selectively only on some (tipically quickly to setup) clocks
> while keep calling the sleeping .prepare on some other (slower ones to
> settle). (while keeping all the other slower clk_rate setup ops non-atomic)
>
> So in v6/v7 I changed the API to provide both sleepable and atomic clk APIs
> when the underlying SCMI stack support atomic mode: this way, though, it is
> clearly up to the caller to decide what to do and if, generally, the
> clock framework just calls everytime both, it will result in a double
> enable.
>
> Was my understanding of the reqs about being able to selectively choose
> the sleep_vs_atomic mode in this way wrong ?

At clk framework level, a user must always call clk_prepare then
clk_enable. Usually clk_prepare is used to do action that can take
time like locking a pll and clk_prepare do the short and atomic action
like gating the clk.

Then, clk_prepare can be a nop if a clk is only doing clk gating as an
example. The same can happen for clk_enable when a pll can't be gated
as an example

What I wanted to say when we discussed offline is that scmi can
provide some PLL and some simple IP clock gating. The PLL would want
to be enabled during the clk_prepare because it's take time and you
can even sleep whereas IP clock gating want to be atomic
So scmi clock 0 might be a PLL with clk_prepare == scmi_clock_enable
and clk_enable == nop
but scmi clock 1 could the clock gating of a HW ip and want
clk_prepare == nop and clk_enable == scmi_clock_atomic_enable

>
> > In case of atomic mode, the clk_prepare should  be a nop
> >
>
> I can certainly revert to use the old exclusive approach, not providing
> a .prepare when atomic is supported, but then all clock enable ops on any
> clock defined on the system will be operated atomically withot any choice
> when atomic SCMI transactions are available.
>
> Ideally, we could like, on a SCMI system supporting atomic, to be able to
> 'tag' a specific clock something like 'prefer-non-atomic' and so selectively
> 'noppify' the .prepare or the .enable at the SCMI clk-driver level depending
> on such tag, but I cannot see any way to expose this from the CLK framework

Yes that would be the right behaviour IMHO

> API or DT, nor it seems suitable for a per-clock DT config option AND it
> would break the current logic of clk_is_enabled_when_prepared().
>
> Indeed clk_is_enabled_when_prepared() logic is ALREADY broken also by this V7
> since when providing also .enable/.disable on atomic transports, the core CLK
> framework would return clk_is_enabled_when_prepared() --> False which does
> NOT fit reality since our SCMI prepare/unprepare DO enable/disable clks even
> if .disable/.enable are provided too.
>
> Probably this last observation on clk_is_enabled_when_prepared() is enough
> to revert to the exclusive atomic/non-atomic approach and just ignore the
> customer wish to be able to selectively choose which clock to operate in
> atomic mode.

Another thing to keep in mind is the use of clk_prepare and clk_enable

clk_prepare/unprepare is usually called when you open/close a driver
whereas clk_enable/disable is called close to the use of the HW ip for
power consumption consideration. If you only use clk_prepare, the IP
will be clocked much more than needed. But if you alwayse use
clk_enable with atomic transfer, you end up taking lot of time to
enable your IP because the parent PLL will be locked at that time in
addition to miss some timing requirement

>
> Any thoughs before a V8 ?
>
> Thanks,
> Cristian
>

Re: [PATCH v7 16/16] clk: scmi: Support atomic clock enable/disable API

[Cristian Marussi]

On Fri, Dec 10, 2021 at 03:27:02PM +0100, Vincent Guittot wrote:
> On Fri, 10 Dec 2021 at 14:30, Cristian Marussi <cristian.marussi@arm.com> wrote:
> >
> > On Fri, Dec 10, 2021 at 11:52:39AM +0100, Vincent Guittot wrote:
> > > Hi Cristian,
> > >

Hi,

> >
> > Hi Vincent,
> >
> > thanks for the feedback, my replies below.
> >
> > > On Mon, 29 Nov 2021 at 20:13, Cristian Marussi <cristian.marussi@arm.com> wrote:
> > > >
> > > > Support also atomic enable/disable clk_ops beside the bare non-atomic one
> > > > (prepare/unprepare) when the underlying SCMI transport is configured to
> > > > support atomic transactions for synchronous commands.
> > > >
> > > > Cc: Michael Turquette <mturquette@baylibre.com>
> > > > Cc: Stephen Boyd <sboyd@kernel.org>
> > > > Cc: linux-clk@vger.kernel.org
> > > > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> > > > ---
> > > > V5 --> V6
> > > > - add concurrent availability of atomic and non atomic reqs
> > > > ---
> > > >  drivers/clk/clk-scmi.c | 56 +++++++++++++++++++++++++++++++++++-------
> > > >  1 file changed, 47 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
> > > > index 1e357d364ca2..50033d873dde 100644
> > > > --- a/drivers/clk/clk-scmi.c
> > > > +++ b/drivers/clk/clk-scmi.c
> > > > @@ -88,21 +88,53 @@ static void scmi_clk_disable(struct clk_hw *hw)
> > > >         scmi_proto_clk_ops->disable(clk->ph, clk->id);
> > > >  }
> > > >
> > > > +static int scmi_clk_atomic_enable(struct clk_hw *hw)
> > > > +{
> > > > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > > > +
> > > > +       return scmi_proto_clk_ops->enable_atomic(clk->ph, clk->id);
> > > > +}
> > > > +
> > > > +static void scmi_clk_atomic_disable(struct clk_hw *hw)
> > > > +{
> > > > +       struct scmi_clk *clk = to_scmi_clk(hw);
> > > > +
> > > > +       scmi_proto_clk_ops->disable_atomic(clk->ph, clk->id);
> > > > +}
> > > > +
> > > > +/*
> > > > + * We can provide enable/disable atomic callbacks only if the underlying SCMI
> > > > + * transport for an SCMI instance is configured to handle SCMI commands in an
> > > > + * atomic manner.
> > > > + *
> > > > + * When no SCMI atomic transport support is available we instead provide only
> > > > + * the prepare/unprepare API, as allowed by the clock framework when atomic
> > > > + * calls are not available.
> > > > + *
> > > > + * Two distinct sets of clk_ops are provided since we could have multiple SCMI
> > > > + * instances with different underlying transport quality, so they cannot be
> > > > + * shared.
> > > > + */
> > > >  static const struct clk_ops scmi_clk_ops = {
> > > >         .recalc_rate = scmi_clk_recalc_rate,
> > > >         .round_rate = scmi_clk_round_rate,
> > > >         .set_rate = scmi_clk_set_rate,
> > > > -       /*
> > > > -        * We can't provide enable/disable callback as we can't perform the same
> > > > -        * in atomic context. Since the clock framework provides standard API
> > > > -        * clk_prepare_enable that helps cases using clk_enable in non-atomic
> > > > -        * context, it should be fine providing prepare/unprepare.
> > > > -        */
> > > >         .prepare = scmi_clk_enable,
> > > >         .unprepare = scmi_clk_disable,
> > > >  };
> > > >
> > > > -static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
> > > > +static const struct clk_ops scmi_atomic_clk_ops = {
> > > > +       .recalc_rate = scmi_clk_recalc_rate,
> > > > +       .round_rate = scmi_clk_round_rate,
> > > > +       .set_rate = scmi_clk_set_rate,
> > > > +       .prepare = scmi_clk_enable,
> > > > +       .unprepare = scmi_clk_disable,
> > > > +       .enable = scmi_clk_atomic_enable,
> > >
> > > For  each clock, we have to start with  clk_prepare and then clk_enable
> > > this means that for scmi clk we will do
> > > scmi_clk_enable
> > > then
> > > scmi_clk_atomic_enable
> > >
> > > scmi_clk_enable and scmi_clk_atomic_enable ends up doing the same
> > > thing: scmi_clock_config_set but the atomic version doesn't sleep
> > >
> > > So you will set enable twice the clock.
> > >
> > > This is confirmed when testing your series with virtio scmi backend as
> > > I can see to consecutive scmi clk set enable request for the same
> > > clock
> > >
> >
> > Yes, I saw that double enable while testing with CLK debugfs entry BUT I
> > thought that was due to the design of the debugfs entries (that calls
> > prepare_enable and so prepare and enable in sequence) also becauase, a few
> > versions ago, this series WAS indeed providing (beside bugs :P) the
> > sleeping prepare XOR the atomic enable depending on the SCMI atomic support
> > state (as you are suggesting now), BUT, after a few offline chats with you,
> > my (probably faulty) understanding was that some partners, even on a system
> > supporting atomic SCMI transfers, would have liked to be able to call the
> > atomic .enable selectively only on some (tipically quickly to setup) clocks
> > while keep calling the sleeping .prepare on some other (slower ones to
> > settle). (while keeping all the other slower clk_rate setup ops non-atomic)
> >
> > So in v6/v7 I changed the API to provide both sleepable and atomic clk APIs
> > when the underlying SCMI stack support atomic mode: this way, though, it is
> > clearly up to the caller to decide what to do and if, generally, the
> > clock framework just calls everytime both, it will result in a double
> > enable.
> >
> > Was my understanding of the reqs about being able to selectively choose
> > the sleep_vs_atomic mode in this way wrong ?
> 
> At clk framework level, a user must always call clk_prepare then
> clk_enable. Usually clk_prepare is used to do action that can take
> time like locking a pll and clk_prepare do the short and atomic action
> like gating the clk.
>

Ok, I was missing this, I supposed was up to the caller decide when to
use what and if to use both or no.

> Then, clk_prepare can be a nop if a clk is only doing clk gating as an
> example. The same can happen for clk_enable when a pll can't be gated
> as an example
> 
> What I wanted to say when we discussed offline is that scmi can
> provide some PLL and some simple IP clock gating. The PLL would want
> to be enabled during the clk_prepare because it's take time and you
> can even sleep whereas IP clock gating want to be atomic
> So scmi clock 0 might be a PLL with clk_prepare == scmi_clock_enable
> and clk_enable == nop
> but scmi clock 1 could the clock gating of a HW ip and want
> clk_prepare == nop and clk_enable == scmi_clock_atomic_enable
> 

Yes that difference in 'enabling-time' was clear, but I was assuming that
the caller was in charge to decide which primitive to use based on the
specific clock characteristics so that custom ops per-clock would have
not be needed.

Because in this scenario instead I will certainly need some descriptor
somewhere to discriminate one 'slow' clock having only .prepare sleep
method from a 'fast' one that will be served by atomic .enable instead...
...and I can already sense the next diatribe about matching the clock
by-clock-id vs by-clock-name ... :P

I'll take this offline with Sudeep, to explore also the possibility to
delegate instead such a descriptor to the SCMI protocol itself.

Thanks for your explanation.

> >
> > > In case of atomic mode, the clk_prepare should  be a nop
> > >
> >
> > I can certainly revert to use the old exclusive approach, not providing
> > a .prepare when atomic is supported, but then all clock enable ops on any
> > clock defined on the system will be operated atomically withot any choice
> > when atomic SCMI transactions are available.
> >
> > Ideally, we could like, on a SCMI system supporting atomic, to be able to
> > 'tag' a specific clock something like 'prefer-non-atomic' and so selectively
> > 'noppify' the .prepare or the .enable at the SCMI clk-driver level depending
> > on such tag, but I cannot see any way to expose this from the CLK framework
> 
> Yes that would be the right behaviour IMHO
> 

As said above the remaining thing to determine is where to get from this
information about the nature of the clock at hand...

> > API or DT, nor it seems suitable for a per-clock DT config option AND it
> > would break the current logic of clk_is_enabled_when_prepared().
> >
> > Indeed clk_is_enabled_when_prepared() logic is ALREADY broken also by this V7
> > since when providing also .enable/.disable on atomic transports, the core CLK
> > framework would return clk_is_enabled_when_prepared() --> False which does
> > NOT fit reality since our SCMI prepare/unprepare DO enable/disable clks even
> > if .disable/.enable are provided too.
> >
> > Probably this last observation on clk_is_enabled_when_prepared() is enough
> > to revert to the exclusive atomic/non-atomic approach and just ignore the
> > customer wish to be able to selectively choose which clock to operate in
> > atomic mode.
> 
> Another thing to keep in mind is the use of clk_prepare and clk_enable
> 
> clk_prepare/unprepare is usually called when you open/close a driver
> whereas clk_enable/disable is called close to the use of the HW ip for
> power consumption consideration. If you only use clk_prepare, the IP
> will be clocked much more than needed. But if you alwayse use
> clk_enable with atomic transfer, you end up taking lot of time to
> enable your IP because the parent PLL will be locked at that time in
> addition to miss some timing requirement
> 

So this is another reason to use the above schema of per-clock custom
enable operation based on the nature of the clock, so that at least the
polling behavior is not used in case of slow PLL-like clocks that long
to acquire.

Thanks,
Cristian