[PATCH] drm/stm: ltdc: use crtc_mode_fixup to update adjusted_mode clock

[Philippe Cornu]

There is a difference between the panel/bridge requested pixel clock
value and the real one due to the hw platform clock preciseness (pll,
dividers...). This patch updates the adjusted_mode clock value with
the real hw clock value so then attached encoder & connector can use
it for precise timing computations.

Signed-off-by: Philippe Cornu <philippe.co...@st.com>
---
 drivers/gpu/drm/stm/ltdc.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index b48589343ae1..90b3de516c91 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -428,12 +428,35 @@ static void ltdc_crtc_atomic_disable(struct drm_crtc 
*crtc,
        reg_set(ldev->regs, LTDC_SRCR, SRCR_IMR);
 }
 
+static bool ltdc_crtc_mode_fixup(struct drm_crtc *crtc,
+                                const struct drm_display_mode *mode,
+                                struct drm_display_mode *adjusted_mode)
+{
+       struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+       int rate = mode->clock * 1000;
+
+       /*
+        * TODO clk_round_rate() does not work yet. When ready, it can
+        * be used instead of clk_set_rate() then clk_get_rate().
+        */
+
+       clk_disable(ldev->pixel_clk);
+       if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
+               DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
+               return false;
+       }
+       clk_enable(ldev->pixel_clk);
+
+       adjusted_mode->clock = clk_get_rate(ldev->pixel_clk) / 1000;
+
+       return true;
+}
+
 static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 {
        struct ltdc_device *ldev = crtc_to_ltdc(crtc);
        struct drm_display_mode *mode = &crtc->state->adjusted_mode;
        struct videomode vm;
-       int rate = mode->clock * 1000;
        u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
        u32 total_width, total_height;
        u32 val;
@@ -456,15 +479,6 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
        total_width = accum_act_w + vm.hfront_porch;
        total_height = accum_act_h + vm.vfront_porch;
 
-       clk_disable(ldev->pixel_clk);
-
-       if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
-               DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
-               return;
-       }
-
-       clk_enable(ldev->pixel_clk);
-
        /* Configures the HS, VS, DE and PC polarities. Default Active Low */
        val = 0;
 
@@ -528,6 +542,7 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc *crtc,
 }
 
 static const struct drm_crtc_helper_funcs ltdc_crtc_helper_funcs = {
+       .mode_fixup = ltdc_crtc_mode_fixup,
        .mode_set_nofb = ltdc_crtc_mode_set_nofb,
        .atomic_flush = ltdc_crtc_atomic_flush,
        .atomic_enable = ltdc_crtc_atomic_enable,
-- 
2.15.1

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