[PATCH master] video: IPUv3-LDB: fix LVDS serial clock configuration

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

The precision improvement in Commit af3d99396a8b ("clk: imx: improve
precision of AV PLL to 1 Hz") broke the LVDS boot splash on the
imx6q-skov-reve-mi1010ait-1cp1 board, because recalculating the clock
rates broke the 7-fold relation between 7MHz pixel clock and the serial
clock.

Before:

pll5_video (rate 980041992
    pll5_post_div (rate 490020996
        pll5_video_div (rate 490020996
            ldb_di0_sel (rate 490020996		   <-- 49MHz / 7 = 7 MHz
                ldb_di0_div_3_5 (rate 140005998                        |
                    ldb_di0_podf (rate 70002999                        ≈
                        ipu1_di0_sel (rate 70002999                    |
                            ipu1_di0 (rate 70002999                    v
                                2400000.ipu@2400000.of_di0_pixel (rate 70002992

After:

pll5_video (rate 980042001
    pll5_post_div (rate 980042001
        pll5_video_div (rate 980042001
            ldb_di0_sel (rate 980042001		  <-- 98MHz / 7 = 14 MHz
                ldb_di0_div_3_5 (rate 280012000                        |
                    ldb_di0_podf (rate 140006000                       ≉
                        ipu1_di0_sel (rate 140006000                   |
                            ipu1_di0 (rate 140006000                   v
                                2400000.ipu@2400000.of_di0_pixel (rate 70002992

By adding an explicit clk_set_rate to the 7-fold frequency before
setting the pixel clock, we restore the ratio again:

pll5_video (rate 980042000
        pll5_post_div (rate 980042000
            pll5_video_div (rate 490021000
                ldb_di0_sel (rate 490021000              <-- 49MHz / 7 = 7 MHz
                    ldb_di0_div_3_5 (rate 140006000                      |
                        ldb_di0_podf (rate 70003000                      ≈
                            ipu1_di0_sel (rate 70003000                  |
                                ipu1_di0 (rate 70003000                  v
                                    2400000.ipu@2400000.of_di0_pixel (rate 70002992

Fixes: af3d99396a8b ("clk: imx: improve precision of AV PLL to 1 Hz")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
Cc: Philipp Zabel <p.zabel@pengutronix.de>

Philipp, I wasn't completely sure about whether the dual frequency
calculation is correct, can you take a look?
---
 drivers/video/imx-ipu-v3/imx-ldb.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/video/imx-ipu-v3/imx-ldb.c b/drivers/video/imx-ipu-v3/imx-ldb.c
index ae7d3548267a..8b9f6d00f6cb 100644
--- a/drivers/video/imx-ipu-v3/imx-ldb.c
+++ b/drivers/video/imx-ipu-v3/imx-ldb.c
@@ -138,9 +138,10 @@ static int imx_ldb_prepare(struct imx_ldb_channel *imx_ldb_ch, struct fb_videomo
 	return 0;
 }
 
-static int imx6q_set_clock(struct imx_ldb *ldb, int ipuno, int dino, int chno, unsigned long pixclk)
+static int imx6q_set_clock(struct imx_ldb *ldb, int ipuno, int dino, int chno,
+			   unsigned long serial_clk, unsigned long di_clk)
 {
-	struct clk *diclk, *ldbclk;
+	struct clk *diclk, *ldbclk, *ldbdiclk;
 	char *clkname;
 	int ret;
 
@@ -160,14 +161,24 @@ static int imx6q_set_clock(struct imx_ldb *ldb, int ipuno, int dino, int chno, u
 		return PTR_ERR(ldbclk);
 	}
 
+	clkname = basprintf("ldb_di%d_sel", chno);
+	ldbdiclk = clk_lookup(clkname);
+	free(clkname);
+	if (IS_ERR(ldbdiclk)) {
+		dev_err(ldb->dev, "failed to get ldb di clk: %pe\n", ldbdiclk);
+		return PTR_ERR(ldbdiclk);
+	}
+
 	ret = clk_set_parent(diclk, ldbclk);
 	if (ret) {
 		dev_err(ldb->dev, "failed to set display clock parent: %pe\n", ERR_PTR(ret));
 		return ret;
 	}
 
-	clk_set_rate(clk_get_parent(ldbclk), pixclk);
-	clk_set_rate(ldbclk, pixclk);
+	clk_set_rate(ldbdiclk, serial_clk);
+
+	clk_set_rate(clk_get_parent(ldbclk), di_clk);
+	clk_set_rate(ldbclk, di_clk);
 
 	return 0;
 }
@@ -189,10 +200,10 @@ static int imx6q_ldb_prepare(struct imx_ldb_channel *imx_ldb_ch, int di,
 		pixclk *= 2;
 
 	if (dual) {
-		imx6q_set_clock(ldb, ipuno, dino, 0, pixclk);
-		imx6q_set_clock(ldb, ipuno, dino, 1, pixclk);
+		imx6q_set_clock(ldb, ipuno, dino, 0, pixclk * 7, pixclk);
+		imx6q_set_clock(ldb, ipuno, dino, 1, pixclk * 7, pixclk);
 	} else {
-		imx6q_set_clock(ldb, ipuno, dino, imx_ldb_ch->chno, pixclk);
+		imx6q_set_clock(ldb, ipuno, dino, imx_ldb_ch->chno, pixclk * 7, pixclk);
 	}
 
 	val = readl(gpr3);
-- 
2.39.5