[v3 1/2] clk: qcom: clk-rcg2: Update logic to calculate D value for RCG

[Taniya Das <tdas@codeaurora.org>]

The display pixel clock has a requirement on certain newer platforms to
support M/N as (2/3) and the final D value calculated results in
underflow errors.
As the current implementation does not check for D value is within
the accepted range for a given M & N value. Update the logic to
calculate the final D value based on the range.

Fixes: 99cbd064b059f ("clk: qcom: Support display RCG clocks")
Signed-off-by: Taniya Das <tdas@codeaurora.org>
---
[v3]
  * Use clamp_t() instead of clamp().
  * Update the commit message for the display use case.

 drivers/clk/qcom/clk-rcg2.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index e1b1b426fae4..b831975a9606 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -264,7 +264,7 @@ static int clk_rcg2_determine_floor_rate(struct clk_hw *hw,

 static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
 {
-	u32 cfg, mask;
+	u32 cfg, mask, d_val, not2d_val, n_minus_m;
 	struct clk_hw *hw = &rcg->clkr.hw;
 	int ret, index = qcom_find_src_index(hw, rcg->parent_map, f->src);

@@ -283,8 +283,17 @@ static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
 		if (ret)
 			return ret;

+		/* Calculate 2d value */
+		d_val = f->n;
+
+		n_minus_m = f->n - f->m;
+		n_minus_m *= 2;
+
+		d_val = clamp_t(u32, d_val, f->m, n_minus_m);
+		not2d_val = ~d_val & mask;
+
 		ret = regmap_update_bits(rcg->clkr.regmap,
-				RCG_D_OFFSET(rcg), mask, ~f->n);
+				RCG_D_OFFSET(rcg), mask, not2d_val);
 		if (ret)
 			return ret;
 	}
--
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