Re: [PATCH 3/6] drm: rcar-du: Fix LVDS stop sequence

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On 18/01/2023 23:12, Laurent Pinchart wrote:
Hi Tomi,

Thank you for the patch.

On Tue, Jan 17, 2023 at 03:51:51PM +0200, Tomi Valkeinen wrote:
From: Koji Matsuoka <koji.matsuoka.xm@xxxxxxxxxxx>

According to H/W manual, LVDCR0 register must be cleared bit by bit when

s@H/W@the hardware/

disabling LVDS.

I don't like this much, but I think I'll stop fighting :-)

Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@xxxxxxxxxxx>
Signed-off-by: LUU HOAI <hoai.luu.ub@xxxxxxxxxxx>
[tomi.valkeinen: simplified the code a bit]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@xxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/rcar-du/rcar_lvds.c | 27 ++++++++++++++++++++++++++-
  1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
index 674b727cdaa2..01800cef1c33 100644
--- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
+++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
@@ -87,6 +87,11 @@ static void rcar_lvds_write(struct rcar_lvds *lvds, u32 reg, u32 data)
  	iowrite32(data, lvds->mmio + reg);
  }
+static u32 rcar_lvds_read(struct rcar_lvds *lvds, u32 reg)
+{
+	return ioread32(lvds->mmio + reg);
+}

Could you please move read before write ?

Sure.

+
  /* -----------------------------------------------------------------------------
   * PLL Setup
   */
@@ -549,8 +554,28 @@ static void rcar_lvds_atomic_disable(struct drm_bridge *bridge,
  				     struct drm_bridge_state *old_bridge_state)
  {
  	struct rcar_lvds *lvds = bridge_to_rcar_lvds(bridge);
+	u32 lvdcr0;
+
+	lvdcr0 = rcar_lvds_read(lvds, LVDCR0);
+
+	lvdcr0 &= ~LVDCR0_LVRES;
+	rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+
+	if (lvds->info->quirks & RCAR_LVDS_QUIRK_GEN3_LVEN) {
+		lvdcr0 &= ~LVDCR0_LVEN;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}
+
+	if (lvds->info->quirks & RCAR_LVDS_QUIRK_PWD) {
+		lvdcr0 &= ~LVDCR0_PWD;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}
+
+	if (!(lvds->info->quirks & RCAR_LVDS_QUIRK_EXT_PLL)) {
+		lvdcr0 &= ~LVDCR0_PLLON;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}

This will leave LVDCR0_BEN and LVDCR0_LVEN on Gen2. Is that fine ?

I don't know, I don't have the manuals or HW. But your point is a bit worrying.

I think we can just do a rcar_lvds_write(lvds, LVDCR0, 0) after the above shenanigans, to make sure everything is disabled. The HW manual doesn't tell us to do that, though, on gen3. Do you think that will be a problem?

And I'm not fully serious with the last sentence...

 Tomi




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