Re: [PATCH 8/8] drm/tidss: Enable Dual and Duplicate Modes for OLDI

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Hi,

On 19/07/2022 11:08, Aradhya Bhatia wrote:
The AM625 DSS peripheral supports 2 OLDI TXes which can work to enable 2
duplicated displays of smaller resolutions or enable a single Dual-Link
display with a higher resolution (1920x1200).

Configure the necessary register to enable the different modes.

Signed-off-by: Aradhya Bhatia <a-bhatia1@xxxxxx>
---
  drivers/gpu/drm/tidss/tidss_dispc.c | 44 +++++++++++++++++++++++++++--
  1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index 0b9689453ee8..28cb61259471 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -1021,8 +1021,8 @@ static void dispc_enable_oldi(struct dispc_device *dispc, u32 hw_videoport,
  	int count = 0;
/*
-	 * For the moment DUALMODESYNC, MASTERSLAVE, MODE, and SRC
-	 * bits of DISPC_VP_DSS_OLDI_CFG are set statically to 0.
+	 * For the moment MASTERSLAVE, and SRC bits of DISPC_VP_DSS_OLDI_CFG are
+	 * set statically to 0.
  	 */
if (fmt->data_width == 24)
@@ -1039,7 +1039,45 @@ static void dispc_enable_oldi(struct dispc_device *dispc, u32 hw_videoport,
oldi_cfg |= BIT(0); /* ENABLE */ - dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+	/*
+	 * As per all the current implementations of DSS, the OLDI TXes are present only on
+	 * hw_videoport = 0 (OLDI TX 0). However, the config register for 2nd OLDI TX (OLDI TX 1)
+	 * is present in the address space of hw_videoport = 1. Hence, using "hw_videoport + 1" to
+	 * configure OLDI TX 1.
+	 */
+
+	switch (dispc->oldi_mode) {
+	case OLDI_MODE_OFF:
+		oldi_cfg &= ~BIT(0); /* DISABLE */
+		dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		dispc_vp_write(dispc, hw_videoport + 1, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		break;
+
+	case OLDI_SINGLE_LINK_SINGLE_MODE_0:
+		dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		break;
+
+	case OLDI_SINGLE_LINK_SINGLE_MODE_1:
+		dispc_vp_write(dispc, hw_videoport + 1, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		break;
+
+	case OLDI_SINGLE_LINK_DUPLICATE_MODE:
+		oldi_cfg |= BIT(5); /* DUPLICATE MODE */
+		dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		dispc_vp_write(dispc, hw_videoport + 1, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		break;
+
+	case OLDI_DUAL_LINK:
+		oldi_cfg |= BIT(11); /* DUALMODESYNC */
+		dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		dispc_vp_write(dispc, hw_videoport + 1, DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
+		break;
+
+	default:
+		dev_warn(dispc->dev, "%s: Incorrect oldi mode. Returning.\n",
+			 __func__);
+		return;
+	}
while (!(oldi_reset_bit & dispc_read(dispc, DSS_SYSSTATUS)) &&
  	       count < 10000)

This feels a bit hacky:

- The function is dispc_enable_oldi, but the above code also disables oldi. We have code in dispc_vp_unprepare() which disables OLDI at the moment.

- The function takes hw_videoport as a parameter, and is designed to work on that videoport. The above operates on two videoports. Isn't the function also called for hw_videoport +1, which would result in reg writes to hw_videoport + 2?

- No matching code in dispc_vp_unprepare

Obviously the duplicate mode (I presume that's "cloning") and the dual link complicate things here, and I have to say I haven't worked with such setups. But I think somehow this should be restructured so that common configuration (common to the OLDIs) is done somewhere else.

I would guess that there are other drivers that support cloning and dual mode. Did you have a look how they handle things?

 Tomi



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