[PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK_REG

[Roman Beranek]

In the case of DSI output, the value of SUN4I_TCON0_DCLK_DIV (4) does
not represent the actual dotclock divider, PLL_MIPI instead runs at
(bpp / lanes )-multiple [1] of the dotclock. [2] Setting 4 as dotclock
divder thus leads to reduced frame rate, specifically by 1/3 on 4-lane
panels, and by 2/3 on 2-lane panels respectively.

As sun4i_dotclock driver stores its calculated divider directly in
the register, conditional handling of the DSI output scenario is needed.
Instead of reading the divider from SUN4I_TCON0_DCLK_REG, retrieve
the value from tcon->dclk_min_div.

[1] bits per pixel / number of DSI lanes
[2] https://github.com/BPI-SINOVOIP/BPI-M64-bsp-4.4/blob/66bef0f2f30b367eb93b1cbad21ce85e0361f7ae/linux-sunxi/drivers/video/fbdev/sunxi/disp2/disp/de/lowlevel_sun50iw1/disp_al.c#L322

Signed-off-by: Roman Beranek <romanberanek@xxxxxxxxxx>
---
 drivers/gpu/drm/sun4i/sun4i_dotclock.c | 6 +++++-
 drivers/gpu/drm/sun4i/sun4i_tcon.c     | 5 +++--
 drivers/gpu/drm/sun4i/sun4i_tcon.h     | 1 +
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
index 417ade3d2565..26fa99aff590 100644
--- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c
+++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
@@ -11,6 +11,7 @@
 
 #include "sun4i_tcon.h"
 #include "sun4i_dotclock.h"
+#include "sun6i_mipi_dsi.h"
 
 struct sun4i_dclk {
 	struct clk_hw		hw;
@@ -56,6 +57,9 @@ static unsigned long sun4i_dclk_recalc_rate(struct clk_hw *hw,
 	struct sun4i_dclk *dclk = hw_to_dclk(hw);
 	u32 val;
 
+	if (dclk->tcon->is_dsi)
+		return parent_rate / dclk->tcon->dclk_min_div;
+
 	regmap_read(dclk->regmap, SUN4I_TCON0_DCLK_REG, &val);
 
 	val >>= SUN4I_TCON0_DCLK_DIV_SHIFT;
@@ -116,7 +120,7 @@ static int sun4i_dclk_set_rate(struct clk_hw *hw, unsigned long rate,
 			       unsigned long parent_rate)
 {
 	struct sun4i_dclk *dclk = hw_to_dclk(hw);
-	u8 div = parent_rate / rate;
+	u8 div = dclk->tcon->is_dsi ? SUN6I_DSI_TCON_DIV : parent_rate / rate;
 
 	return regmap_update_bits(dclk->regmap, SUN4I_TCON0_DCLK_REG,
 				  GENMASK(6, 0), div);
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 523a6d787921..7f5d3c135058 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -367,8 +367,9 @@ static void sun4i_tcon0_mode_set_cpu(struct sun4i_tcon *tcon,
 	u32 block_space, start_delay;
 	u32 tcon_div;
 
-	tcon->dclk_min_div = SUN6I_DSI_TCON_DIV;
-	tcon->dclk_max_div = SUN6I_DSI_TCON_DIV;
+	tcon->is_dsi = true;
+	tcon->dclk_min_div = bpp / lanes;
+	tcon->dclk_max_div = bpp / lanes;
 
 	sun4i_tcon0_mode_set_common(tcon, mode);
 
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index fa23aa23fe4a..d8150ba2f319 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -271,6 +271,7 @@ struct sun4i_tcon {
 	struct clk			*dclk;
 	u8				dclk_max_div;
 	u8				dclk_min_div;
+	bool				is_dsi;
 
 	/* Reset control */
 	struct reset_control		*lcd_rst;
-- 
2.32.0 (Apple Git-132)