[PATCH v2 04/20] drm/tilcdc: Add support for DRM bus flags and simplify panel config

Kory Maincent (TI.com)
2025-12-11T16:39:54Z

Migrate CRTC mode configuration to use standard DRM bus flags in
preparation for removing the tilcdc_panel driver and its custom
tilcdc_panel_info structure.

Add support for DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE and
DRM_BUS_FLAG_SYNC_DRIVE_NEGEDGE flags to control pixel clock and sync
signal edge polarity, while maintaining backward compatibility with the
existing tilcdc panel info structure.

Simplify several hardware parameters by setting them to fixed defaults
based on common usage across existing device trees:
- DMA burst size: 16 (previously configurable via switch statement)
- AC bias frequency: 255 (previously panel-specific)
- FIFO DMA request delay: 128 (previously panel-specific)

These parameters show no variation in real-world usage, so hardcoding
them simplifies the driver without losing functionality.

Preserve FIFO threshold configurability by detecting the SoC type, as
this parameter varies between AM33xx (8) and DA850 (16) platforms.

Signed-off-by: Kory Maincent (TI.com) <kory.maincent@bootlin.com>
---

Change in v2:
- Use SoC type instead of devicetree parameter to set FIFO threshold
value.
---
drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 47 +++++++++++++-----------------------
drivers/gpu/drm/tilcdc/tilcdc_drv.c | 29 ++++++++++++++++------
drivers/gpu/drm/tilcdc/tilcdc_drv.h | 2 ++
3 files changed, 41 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index b06b1453db2dd..2309a9a0c925d 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -285,27 +285,15 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)

/* Configure the Burst Size and fifo threshold of DMA: */
reg = tilcdc_read(dev, LCDC_DMA_CTRL_REG) & ~0x00000770;
- switch (info->dma_burst_sz) {
- case 1:
- reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_1);
- break;
- case 2:
- reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_2);
- break;
- case 4:
- reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_4);
- break;
- case 8:
- reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_8);
- break;
- case 16:
- reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_16);
- break;
- default:
- dev_err(dev->dev, "invalid burst size\n");
- return;
+ /* Use 16 bit DMA burst size by default */
+ reg |= LCDC_DMA_BURST_SIZE(LCDC_DMA_BURST_16);
+ if (priv->fifo_th) {
+ int fifo_th_val = ilog2(priv->fifo_th) - 3;
+
+ reg |= (fifo_th_val << 8);
+ } else {
+ reg |= (info->fifo_th << 8);
}
- reg |= (info->fifo_th << 8);
tilcdc_write(dev, LCDC_DMA_CTRL_REG, reg);

/* Configure timings: */
@@ -321,8 +309,8 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)

/* Set AC Bias Period and Number of Transitions per Interrupt: */
reg = tilcdc_read(dev, LCDC_RASTER_TIMING_2_REG) & ~0x000fff00;
- reg |= LCDC_AC_BIAS_FREQUENCY(info->ac_bias) |
- LCDC_AC_BIAS_TRANSITIONS_PER_INT(info->ac_bias_intrpt);
+ /* Use 255 AC Bias Pin Frequency by default */
+ reg |= LCDC_AC_BIAS_FREQUENCY(255);

/*
* subtract one from hfp, hbp, hsw because the hardware uses
@@ -392,20 +380,19 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)
return;
}
}
- reg |= info->fdd << 12;
+ /* Use 128 FIFO DMA Request Delay by default */
+ reg |= 128 << 12;
tilcdc_write(dev, LCDC_RASTER_CTRL_REG, reg);

- if (info->invert_pxl_clk)
+ if (info->invert_pxl_clk ||
+ mode->flags == DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
tilcdc_set(dev, LCDC_RASTER_TIMING_2_REG, LCDC_INVERT_PIXEL_CLOCK);
else
tilcdc_clear(dev, LCDC_RASTER_TIMING_2_REG, LCDC_INVERT_PIXEL_CLOCK);

- if (info->sync_ctrl)
- tilcdc_set(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_CTRL);
- else
- tilcdc_clear(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_CTRL);
-
- if (info->sync_edge)
+ tilcdc_set(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_CTRL);
+ if (info->sync_edge ||
+ mode->flags == DRM_BUS_FLAG_SYNC_DRIVE_NEGEDGE)
tilcdc_set(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_EDGE);
else
tilcdc_clear(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_EDGE);
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
index 3dcbec312bacb..60230fa9cec95 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
@@ -31,6 +31,11 @@
#include "tilcdc_panel.h"
#include "tilcdc_regs.h"

+enum {
+ AM33XX_TILCDC,
+ DA850_TILCDC,
+};
+
static LIST_HEAD(module_list);

static const u32 tilcdc_rev1_formats[] = { DRM_FORMAT_RGB565 };
@@ -192,11 +197,19 @@ static void tilcdc_fini(struct drm_device *dev)
drm_dev_put(dev);
}

+static const struct of_device_id tilcdc_of_match[] = {
+ { .compatible = "ti,am33xx-tilcdc", .data = (void *)AM33XX_TILCDC},
+ { .compatible = "ti,da850-tilcdc", .data = (void *)DA850_TILCDC},
+ { },
+};
+MODULE_DEVICE_TABLE(of, tilcdc_of_match);
+
static int tilcdc_init(const struct drm_driver *ddrv, struct device *dev)
{
struct drm_device *ddev;
struct platform_device *pdev = to_platform_device(dev);
struct device_node *node = dev->of_node;
+ const struct of_device_id *of_id;
struct tilcdc_drm_private *priv;
u32 bpp = 0;
int ret;
@@ -209,6 +222,10 @@ static int tilcdc_init(const struct drm_driver *ddrv, struct device *dev)
if (IS_ERR(ddev))
return PTR_ERR(ddev);

+ of_id = of_match_node(tilcdc_of_match, node);
+ if (!of_id)
+ return -ENODEV;
+
ddev->dev_private = priv;
platform_set_drvdata(pdev, ddev);
drm_mode_config_init(ddev);
@@ -309,6 +326,11 @@ static int tilcdc_init(const struct drm_driver *ddrv, struct device *dev)

DBG("Maximum Pixel Clock Value %dKHz", priv->max_pixelclock);

+ if ((unsigned int)of_id->data == DA850_TILCDC)
+ priv->fifo_th = 16;
+ else
+ priv->fifo_th = 8;
+
ret = tilcdc_crtc_create(ddev);
if (ret < 0) {
dev_err(dev, "failed to create crtc\n");
@@ -597,13 +619,6 @@ static void tilcdc_pdev_shutdown(struct platform_device *pdev)
drm_atomic_helper_shutdown(platform_get_drvdata(pdev));
}

-static const struct of_device_id tilcdc_of_match[] = {
- { .compatible = "ti,am33xx-tilcdc", },
- { .compatible = "ti,da850-tilcdc", },
- { },
-};
-MODULE_DEVICE_TABLE(of, tilcdc_of_match);
-
static struct platform_driver tilcdc_platform_driver = {
.probe = tilcdc_pdev_probe,
.remove = tilcdc_pdev_remove,
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.h b/drivers/gpu/drm/tilcdc/tilcdc_drv.h
index 3aba3a1155ba0..79078b4ae7393 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.h
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.h
@@ -61,6 +61,8 @@ struct tilcdc_drm_private {
*/
uint32_t max_width;

+ u32 fifo_th;
+
/* Supported pixel formats */
const uint32_t *pixelformats;
uint32_t num_pixelformats;

--
2.43.0