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Subject[PATCH 6/6] [RFC] clk: scmi: Support atomic clock enable/disable API
Date
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.

Compare the SCMI system-wide configured atomic threshold latency time and
the per-clock advertised enable latency (if any) to choose whether to
provide sleeping prepare/unprepare vs atomic enable/disable.

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>
---
Tagged as RFC since dependent on a previous RFC patch
---
drivers/clk/clk-scmi.c | 71 +++++++++++++++++++++++++++++++++++-------
1 file changed, 60 insertions(+), 11 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index 1e357d364ca2..2c7a830ce308 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c
@@ -2,7 +2,7 @@
/*
* System Control and Power Interface (SCMI) Protocol based clock driver
*
- * Copyright (C) 2018-2021 ARM Ltd.
+ * Copyright (C) 2018-2022 ARM Ltd.
*/

#include <linux/clk-provider.h>
@@ -88,21 +88,51 @@ 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,
+ .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 +140,7 @@ 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,
};

@@ -139,6 +169,8 @@ static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk)
static int scmi_clocks_probe(struct scmi_device *sdev)
{
int idx, count, err;
+ unsigned int atomic_threshold;
+ bool is_atomic;
struct clk_hw **hws;
struct clk_hw_onecell_data *clk_data;
struct device *dev = &sdev->dev;
@@ -168,8 +200,11 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
clk_data->num = count;
hws = clk_data->hws;

+ is_atomic = handle->is_transport_atomic(handle, &atomic_threshold);
+
for (idx = 0; idx < count; idx++) {
struct scmi_clk *sclk;
+ const struct clk_ops *scmi_ops;

sclk = devm_kzalloc(dev, sizeof(*sclk), GFP_KERNEL);
if (!sclk)
@@ -184,13 +219,27 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
sclk->id = idx;
sclk->ph = ph;

- err = scmi_clk_ops_init(dev, sclk);
+ /*
+ * Note that when transport is atomic but SCMI protocol did not
+ * specify (or support) an enable_latency associated with a
+ * clock, we default to use atomic operations mode.
+ */
+ if (is_atomic &&
+ sclk->info->enable_latency <= atomic_threshold)
+ scmi_ops = &scmi_atomic_clk_ops;
+ else
+ scmi_ops = &scmi_clk_ops;
+
+ 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);
hws[idx] = NULL;
} else {
- dev_dbg(dev, "Registered clock:%s\n", sclk->info->name);
+ dev_dbg(dev, "Registered clock:%s%s\n",
+ sclk->info->name,
+ scmi_ops == &scmi_atomic_clk_ops ?
+ " (atomic ops)" : "");
hws[idx] = &sclk->hw;
}
}
--
2.17.1
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