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Message-ID: <f9fb8050-89f9-4449-bc2c-ff284873be79@ti.com>
Date: Tue, 6 Jan 2026 13:30:40 -0600
From: Andrew Davis <afd@...com>
To: "Kory Maincent (TI.com)" <kory.maincent@...tlin.com>, Jyri Sarha
<jyri.sarha@....fi>, Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
<mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
<airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring
<robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
<conor+dt@...nel.org>, Russell King <linux@...linux.org.uk>, "Bartosz
Golaszewski" <brgl@...ev.pl>, Tony Lindgren <tony@...mide.com>, Andrzej Hajda
<andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>,
"Robert Foss" <rfoss@...nel.org>, Laurent Pinchart
<Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, "Jernej
Skrabec" <jernej.skrabec@...il.com>
CC: Markus Schneider-Pargmann <msp@...libre.com>, Bajjuri Praneeth
<praneeth@...com>, Luca Ceresoli <luca.ceresoli@...tlin.com>, Louis Chauvet
<louis.chauvet@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Miguel Gazquez <miguel.gazquez@...tlin.com>, Herve Codina
<herve.codina@...tlin.com>, <dri-devel@...ts.freedesktop.org>,
<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v3 04/22] drm/tilcdc: Add support for DRM bus flags and
simplify panel config
On 1/6/26 11:42 AM, Kory Maincent (TI.com) wrote:
> 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.
>
> Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> Signed-off-by: Kory Maincent (TI.com) <kory.maincent@...tlin.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);
You should be able to use `device_get_match_data()` here, then you would
also be able to keep the tilcdc_of_match table down were it was before.
Andrew
> + 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;
>
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