linux-kernel - [PATCH 3/3] Revert "drm/sun4i: dsi: Rework a bit the hblk calculation"

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Date:   Tue,  1 Oct 2019 16:02:53 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com, Icenowy Zheng <icenowy@...c.io>
Subject: [PATCH 3/3] Revert "drm/sun4i: dsi: Rework a bit the hblk calculation"

This reverts commit 62e7511a4f4dcf07f753893d3424decd9466c98b.

This commit, although claimed as a refactor, in fact changed the
formula.

By expanding the original formula, we can find that the const 10 is not
substracted, instead it's added to the value (because 10 is negative
when calculating hsa, and hsa itself is negative when calculating hblk).
This breaks the similar pattern to other formulas, so restoring the
original formula is more proper.

Signed-off-by: Icenowy Zheng <icenowy@...c.io>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index 2d3e822a7739..cb5fd19c0d0d 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -577,14 +577,9 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
 			  (mode->hsync_start - mode->hdisplay) * Bpp - HFP_PACKET_OVERHEAD);
 
 		/*
-		 * The blanking is set using a sync event (4 bytes)
-		 * and a blanking packet (4 bytes + payload + 2
-		 * bytes). Its minimal size is therefore 10 bytes.
+		 * hblk seems to be the line + porches length.
 		 */
-#define HBLK_PACKET_OVERHEAD	10
-		hblk = max((unsigned int)HBLK_PACKET_OVERHEAD,
-			   (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp -
-			   HBLK_PACKET_OVERHEAD);
+		hblk = mode->htotal * Bpp - hsa;
 
 		/*
 		 * And I'm not entirely sure what vblk is about. The driver in
-- 
2.21.0