On Wed, Aug 12, 2026 at 03:29:50PM +0200, Francesco Dolcini wrote: > From: Francesco Dolcini <[email protected]> > > LCDIF programs LCD_DATABUS_WIDTH from the selected media bus format. The > format reported by the downstream panel or bridge describes the display > input, but it does not describe how the LCDIF data pins are physically > wired on the board. > > These can differ. For example, a 16-bit LCDIF bus can be connected to a > 24-bit display by wiring the available color bits to the corresponding > display inputs. In that case, using the display's 24-bit format to > configure LCDIF selects the wrong data-bus mode and changes the assignment > of color bits on the LCD_DATA pins. > > Read the optional bus-width endpoint property from the LCDIF output port > and use it to select the media bus format used to configure LCDIF. This > allows the LCDIF bus mode to describe the physical interface > independently of the downstream display format. > > When the optional property is absent, or it has an invalid value, continue > using the format reported by the downstream display device, preserving > the existing behavior. The code is not validating the DT for > correctness and just fall back to the previous behavior in case of > errors. > > Signed-off-by: Francesco Dolcini <[email protected]> > ---
Reviewed-by: Frank Li <[email protected]> > v3: improve commit message and make it clear that the code assumes that > the DT is correct, when the DT contains an invalid property value, > the code safely fall-back to the previous behavior > v2: use the common bus-width property instead of the legacy interface-pix-fmt > --- > drivers/gpu/drm/mxsfb/mxsfb_drv.c | 24 ++++++++++++++++++++++++ > drivers/gpu/drm/mxsfb/mxsfb_drv.h | 2 ++ > drivers/gpu/drm/mxsfb/mxsfb_kms.c | 12 ++++++++++++ > 3 files changed, 38 insertions(+) > > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c > b/drivers/gpu/drm/mxsfb/mxsfb_drv.c > index 8b4a500347fb..f8ecc8bbd63c 100644 > --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c > +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c > @@ -12,7 +12,10 @@ > #include <linux/clk.h> > #include <linux/dma-mapping.h> > #include <linux/io.h> > +#include <linux/media-bus-format.h> > #include <linux/module.h> > +#include <linux/of.h> > +#include <linux/of_graph.h> > #include <linux/platform_device.h> > #include <linux/property.h> > #include <linux/pm_runtime.h> > @@ -211,7 +214,10 @@ static int mxsfb_load(struct drm_device *drm, > const struct mxsfb_devdata *devdata) > { > struct platform_device *pdev = to_platform_device(drm->dev); > + struct device_node *np = pdev->dev.of_node; > struct mxsfb_drm_private *mxsfb; > + struct device_node *ep; > + u32 bus_width = 0; > int ret; > > mxsfb = devm_kzalloc(&pdev->dev, sizeof(*mxsfb), GFP_KERNEL); > @@ -238,6 +244,24 @@ static int mxsfb_load(struct drm_device *drm, > if (IS_ERR(mxsfb->clk_disp_axi)) > mxsfb->clk_disp_axi = NULL; > > + ep = of_graph_get_next_endpoint(np, NULL); > + if (ep) { > + of_property_read_u32(ep, "bus-width", &bus_width); > + of_node_put(ep); > + } > + > + switch (bus_width) { > + case 16: > + mxsfb->bus_format = MEDIA_BUS_FMT_RGB565_1X16; > + break; > + case 18: > + mxsfb->bus_format = MEDIA_BUS_FMT_RGB666_1X18; > + break; > + case 24: > + mxsfb->bus_format = MEDIA_BUS_FMT_RGB888_1X24; > + break; > + } > + > ret = dma_set_mask_and_coherent(drm->dev, DMA_BIT_MASK(32)); > if (ret) > return ret; > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.h > b/drivers/gpu/drm/mxsfb/mxsfb_drv.h > index d160d921b25f..bdc47ce5be79 100644 > --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.h > +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.h > @@ -46,6 +46,8 @@ struct mxsfb_drm_private { > struct drm_connector *connector; > struct drm_bridge *bridge; > > + u32 bus_format; > + > bool crc_active; > }; > > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c > b/drivers/gpu/drm/mxsfb/mxsfb_kms.c > index d8ebebc5314b..1d78c486d147 100644 > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c > @@ -386,6 +386,18 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc > *crtc, > if (!bus_format) > bus_format = MEDIA_BUS_FMT_RGB888_1X24; > > + /* > + * Prefer the bus format derived from the OF graph endpoint "bus-width" > + * property when available. Otherwise, use the bus format reported by > + * the downstream bridge or panel. > + * > + * This supports mismatched display and interface bus widths, such as > + * a 24-bit panel connected through an 18-bit interface or an 18-bit > + * panel connected through a 24-bit interface. > + */ > + if (mxsfb->bus_format) > + bus_format = mxsfb->bus_format; > + > mxsfb_crtc_mode_set_nofb(mxsfb, bridge_state, bus_format); > > /* Write cur_buf as well to avoid an initial corrupt frame */ > -- > 2.47.3 > >
