[PATCH 06/12] drm/sun4i: sun6i_mipi_dsi: Fix VBP size calculation

On Thu, Sep 27, 2018 at 09:50:34PM +0530, Jagan Teki wrote:

On Thu, Sep 27, 2018 at 8:51 PM Maxime Ripard [off-list ref] wrote:

quoted

On Thu, Sep 27, 2018 at 05:18:44PM +0530, Jagan Teki wrote:

quoted

According to horizontal and vertical timings are defined
per the diagram from include/drm/drm_modes.h

Back porch = [hv]total - [hv]sync_end

So, update SUN6I_DSI_BASIC_SIZE0_VBP calculation as
mode->vtotal - mode->vsync_end

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index 1c7e42015645..599284971ab6 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

@@ -526,8 +526,8 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
      regmap_write(dsi->regs, SUN6I_DSI_BASIC_SIZE0_REG,
                   SUN6I_DSI_BASIC_SIZE0_VSA(mode->vsync_end -
                                             mode->vsync_start) |
-                  SUN6I_DSI_BASIC_SIZE0_VBP(mode->vsync_start -
-                                            mode->vdisplay));
+                  SUN6I_DSI_BASIC_SIZE0_VBP(mode->vtotal -
+                                            mode->vsync_end));

Is it purely theoretical, or did you find some source that back that?

VSA is done as per that, sync_end - sync start would give sync time.

That's a different register though.

VBP also done in BPI-M64-bsp[1] which results back porch existing code
results fron porch.

[1] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L955

That code does back porch - sync length. Such a calculation doesn't
make much sense as is, but you're saying that it results in the front
porch. Again, what makes you say that?

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com