From: Patrice Chotard <patrice.chot...@st.com>

Implement set_rate() for LTDC clock only, set_rate for other
clocks will be added if needed. This is needed by future LTDC driver
improvements.

Signed-off-by: Patrice Chotard <patrice.chot...@st.com>
---
 drivers/clk/clk_stm32f.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/drivers/clk/clk_stm32f.c b/drivers/clk/clk_stm32f.c
index a11d6dc242ba..a683911ebf00 100644
--- a/drivers/clk/clk_stm32f.c
+++ b/drivers/clk/clk_stm32f.c
@@ -136,6 +136,9 @@ struct stm32_clk {
        unsigned long hse_rate;
 };
 
+#ifdef CONFIG_VIDEO_STM32
+static const u8 plldivr_table[] = { 0, 0, 2, 3, 4, 5, 6, 7 };
+#endif
 static const u8 pllsaidivr_table[] = { 2, 4, 8, 16 };
 
 static int configure_clocks(struct udevice *dev)
@@ -484,7 +487,104 @@ static ulong stm32_clk_get_rate(struct clk *clk)
 
 static ulong stm32_set_rate(struct clk *clk, ulong rate)
 {
+#ifdef CONFIG_VIDEO_STM32
+       struct stm32_clk *priv = dev_get_priv(clk->dev);
+       struct stm32_rcc_regs *regs = priv->base;
+       u32 pllsair_rate, pllsai_vco_rate, current_rate;
+       u32 best_div, best_diff, diff;
+       u16 div;
+       u8 best_plldivr, best_pllsaidivr;
+       u8 i, j;
+       bool found = false;
+
+       /* Only set_rate for LTDC clock is implemented */
+       if (clk->id != STM32F7_APB2_CLOCK(LTDC)) {
+               pr_err("set_rate not implemented for clock index %ld\n",
+                      clk->id);
+               return 0;
+       }
+
+       if (rate == stm32_clk_get_rate(clk))
+               /* already set to requested rate */
+               return rate;
+
+       /* get the current PLLSAIR output freq */
+       pllsair_rate = stm32_clk_get_pllsai_rate(priv, PLLSAIR);
+       best_div = pllsair_rate / rate;
+
+       /* look into pllsaidivr_table if this divider is available*/
+       for (i = 0 ; i < sizeof(pllsaidivr_table); i++)
+               if (best_div == pllsaidivr_table[i]) {
+                       /* set pll_saidivr with found value */
+                       clrsetbits_le32(&regs->dckcfgr,
+                                       RCC_DCKCFGR_PLLSAIDIVR_MASK,
+                                       pllsaidivr_table[i]);
+                       return rate;
+               }
+
+       /*
+        * As no pllsaidivr value is suitable to obtain requested freq,
+        * test all combination of pllsaidivr * pllsair and find the one
+        * which give freq closest to requested rate.
+        */
+
+       pllsai_vco_rate = stm32_clk_get_pllsai_vco_rate(priv);
+       best_diff = ULONG_MAX;
+       best_pllsaidivr = 0;
+       best_plldivr = 0;
+       /*
+        * start at index 2 of plldivr_table as divider value at index 0
+        * and 1 are 0)
+        */
+       for (i = 2; i < sizeof(plldivr_table); i++) {
+               for (j = 0; j < sizeof(pllsaidivr_table); j++) {
+                       div = plldivr_table[i] * pllsaidivr_table[j];
+                       current_rate = pllsai_vco_rate / div;
+                       /* perfect combination is found ? */
+                       if (current_rate == rate) {
+                               best_pllsaidivr = j;
+                               best_plldivr = i;
+                               found = true;
+                               break;
+                       }
+
+                       diff = (current_rate > rate) ?
+                              current_rate - rate : rate - current_rate;
+
+                       /* found a better combination ? */
+                       if (diff < best_diff) {
+                               best_diff = diff;
+                               best_pllsaidivr = j;
+                               best_plldivr = i;
+                       }
+               }
+
+               if (found)
+                       break;
+       }
+
+       /* Disable the SAI PLL */
+       clrbits_le32(&regs->cr, RCC_CR_PLLSAION);
+
+       /* set pll_saidivr with found value */
+       clrsetbits_le32(&regs->dckcfgr, RCC_DCKCFGR_PLLSAIDIVR_MASK,
+                       best_pllsaidivr << RCC_DCKCFGR_PLLSAIDIVR_SHIFT);
+
+       /* set pllsair with found value */
+       clrsetbits_le32(&regs->pllsaicfgr, RCC_PLLSAICFGR_PLLSAIR_MASK,
+                       plldivr_table[best_plldivr]
+                       << RCC_PLLSAICFGR_PLLSAIR_SHIFT);
+
+       /* Enable the SAI PLL */
+       setbits_le32(&regs->cr, RCC_CR_PLLSAION);
+       while (!(readl(&regs->cr) & RCC_CR_PLLSAIRDY))
+               ;
+
+       div = plldivr_table[best_plldivr] * pllsaidivr_table[best_pllsaidivr];
+       return pllsai_vco_rate / div;
+#else
        return 0;
+#endif
 }
 
 static int stm32_clk_enable(struct clk *clk)
-- 
1.9.1

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