On Thu, Sep 27, 2018 at 10:28 PM Maxime Ripard
[off-list ref] wrote:

On Thu, Sep 27, 2018 at 05:18:45PM +0530, Jagan Teki wrote:

quoted

TCON DRQ set bits for non-burst DSI mode can computed via
horizontal front porch instead of front porch + sync timings.

Since there no documentation for TCON_DRQ_REG(0x7c) register
this change is taken as reference from BPI-M64-bsp.

Detailing more what the issue is would be great.

quoted

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 599284971ab6..9918fdb990ff 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

@@ -367,9 +367,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
      struct mipi_dsi_device *device = dsi->device;
      u32 val = 0;

The computation here is in the A64 driver:

if ((panel->lcd_ht - panel->lcd_x - panel->lcd_hbp) < 21) {
        dsi_dev[sel]->dsi_tcon_drq.bits.drq_mode = 0;
} else {
        dsi_dev[sel]->dsi_tcon_drq.bits.drq_set =
                (panel->lcd_ht-panel->lcd_x-panel->lcd_hbp-20) *
                dsi_pixel_bits[panel->lcd_dsi_format]/(8*4);
}

It is testing that the sync + front porch is smaller than 21, and
otherwise sets the drq.

quoted

-     if ((mode->hsync_end - mode->hdisplay) > 20) {

My code here is testing that the difference between hsync_end and
hdisplay is superior to 20, and sets the DRQ if true. The condition is
reversed, but otherwise, that difference is the front porch plus the
sync length.

True, I understand this, but does drq setting here is specific to SoC?
I thought of finding DRQ in A31 BSP but I couldn't find the code. do
you have bsp somewhere in github?

quoted

+     if ((mode->hsync_start - mode->hdisplay) > 20) {

However, you are testing for just the front porch, unlike what your
commit log is saying, and unlike what allwinner's code is saying. So
this deserves some explanation.

but A64 is doing this, do you think it's completely A64 specific or
testing panel with front porch drq?