[PATCH AUTOSEL 6.17-6.12] clk: scmi: migrate round_rate() to determine_rate()

[Sasha Levin]

From: Brian Masney <bmasney at redhat.com>

[ Upstream commit 80cb2b6edd8368f7e1e8bf2f66aabf57aa7de4b7 ]

This driver implements both the determine_rate() and round_rate() clk
ops, and the round_rate() clk ops is deprecated. When both are defined,
clk_core_determine_round_nolock() from the clk core will only use the
determine_rate() clk ops.

The existing scmi_clk_determine_rate() is a noop implementation that
lets the firmware round the rate as appropriate. Drop the existing
determine_rate implementation and convert the existing round_rate()
implementation over to determine_rate().

scmi_clk_determine_rate() was added recently when the clock parent
support was added, so it's not expected that this change will regress
anything.

Reviewed-by: Sudeep Holla <sudeep.holla at arm.com>
Reviewed-by: Peng Fan <peng.fan at nxp.com>
Tested-by: Peng Fan <peng.fan at nxp.com> #i.MX95-19x19-EVK
Signed-off-by: Brian Masney <bmasney at redhat.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES The patch restores the SCMI clock driver's ability to return a valid
rounded rate when the framework asks for it.

- With the regression-introducing stub in `scmi_clk_determine_rate()`
  every request fell through without touching `req->rate`, so
  `clk_core_determine_round_nolock()` would return the caller’s original
  value whenever both ops were present (`drivers/clk/clk.c:1596-1613`),
  making `clk_round_rate()` lie about the hardware outcome on platforms
  that advertise min/max/step limits.
- The new implementation in `drivers/clk/clk-scmi.c:57-90` moves the
  logic that used to live in `.round_rate()` into `.determine_rate()`,
  clamping to `min_rate`/`max_rate` and quantising by `step_size`,
  exactly reproducing the behaviour that worked before the noop
  `determine_rate()` was introduced.
- Discrete-rate clocks remain unchanged—the function still bails out
  early (`drivers/clk/clk-scmi.c:63-71`), matching the old behaviour—and
  the ops table simply stops advertising the deprecated `.round_rate()`
  callback (`drivers/clk/clk-scmi.c:299-304`), so risk is minimal and
  confined to SCMI clocks.
- The bug has shipped since the recent parent-support work (first seen
  in v6.10), so stable kernels carrying that change are returning
  incorrect values to consumers today.

Because this is a regression fix with low risk and no architectural
churn, it is a good candidate for backporting to every stable series
that contains the broken noop `determine_rate()`.

 drivers/clk/clk-scmi.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index d2408403283fc..78dd2d9c7cabd 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c
@@ -54,8 +54,8 @@ static unsigned long scmi_clk_recalc_rate(struct clk_hw *hw,
 	return rate;
 }
 
-static long scmi_clk_round_rate(struct clk_hw *hw, unsigned long rate,
-				unsigned long *parent_rate)
+static int scmi_clk_determine_rate(struct clk_hw *hw,
+				   struct clk_rate_request *req)
 {
 	u64 fmin, fmax, ftmp;
 	struct scmi_clk *clk = to_scmi_clk(hw);
@@ -67,20 +67,27 @@ static long scmi_clk_round_rate(struct clk_hw *hw, unsigned long rate,
 	 * running at then.
 	 */
 	if (clk->info->rate_discrete)
-		return rate;
+		return 0;
 
 	fmin = clk->info->range.min_rate;
 	fmax = clk->info->range.max_rate;
-	if (rate <= fmin)
-		return fmin;
-	else if (rate >= fmax)
-		return fmax;
+	if (req->rate <= fmin) {
+		req->rate = fmin;
+
+		return 0;
+	} else if (req->rate >= fmax) {
+		req->rate = fmax;
 
-	ftmp = rate - fmin;
+		return 0;
+	}
+
+	ftmp = req->rate - fmin;
 	ftmp += clk->info->range.step_size - 1; /* to round up */
 	do_div(ftmp, clk->info->range.step_size);
 
-	return ftmp * clk->info->range.step_size + fmin;
+	req->rate = ftmp * clk->info->range.step_size + fmin;
+
+	return 0;
 }
 
 static int scmi_clk_set_rate(struct clk_hw *hw, unsigned long rate,
@@ -119,15 +126,6 @@ static u8 scmi_clk_get_parent(struct clk_hw *hw)
 	return p_idx;
 }
 
-static int scmi_clk_determine_rate(struct clk_hw *hw, struct clk_rate_request *req)
-{
-	/*
-	 * Suppose all the requested rates are supported, and let firmware
-	 * to handle the left work.
-	 */
-	return 0;
-}
-
 static int scmi_clk_enable(struct clk_hw *hw)
 {
 	struct scmi_clk *clk = to_scmi_clk(hw);
@@ -300,7 +298,6 @@ scmi_clk_ops_alloc(struct device *dev, unsigned long feats_key)
 
 	/* Rate ops */
 	ops->recalc_rate = scmi_clk_recalc_rate;
-	ops->round_rate = scmi_clk_round_rate;
 	ops->determine_rate = scmi_clk_determine_rate;
 	if (feats_key & BIT(SCMI_CLK_RATE_CTRL_SUPPORTED))
 		ops->set_rate = scmi_clk_set_rate;
-- 
2.51.0