Re: [PATCH 2/3] drm: lcdif: Use dedicated set/clr registers for polarity/edge
From: Lucas Stach <l.stach@pengutronix.de>
Date: 2026-03-31 09:09:42
Also in:
dri-devel, imx, lkml
Hi Paul, Am Dienstag, dem 31.03.2026 um 00:46 +0200 schrieb Paul Kocialkowski:
The lcdif v3 hardware comes with dedicated registers to set and clear polarity bits in the CTRL register. It is unclear if there is a difference with writing to the CTRL register directly. Follow the NXP BSP reference by using these registers, in case there is a subtle difference caused by using them.
I don't really like that patch, as it blows up what is currently a single register access to three separate ones. If there is no clear benefit (as in it has been shown to fix any issue), I would prefer this code to stay as-is. Regards, Lucas
quoted hunk ↗ jump to hunk
Signed-off-by: Paul Kocialkowski <paulk@sys-base.io> --- drivers/gpu/drm/mxsfb/lcdif_kms.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c index a00c4f6d63f4..1aac354041c7 100644 --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c@@ -296,18 +296,27 @@ static void lcdif_set_formats(struct lcdif_drm_private *lcdif, static void lcdif_set_mode(struct lcdif_drm_private *lcdif, u32 bus_flags) { struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode; - u32 ctrl = 0; + u32 ctrl; if (m->flags & DRM_MODE_FLAG_NHSYNC) - ctrl |= CTRL_INV_HS; + writel(CTRL_INV_HS, lcdif->base + LCDC_V8_CTRL + REG_SET); + else + writel(CTRL_INV_HS, lcdif->base + LCDC_V8_CTRL + REG_CLR); + if (m->flags & DRM_MODE_FLAG_NVSYNC) - ctrl |= CTRL_INV_VS; + writel(CTRL_INV_VS, lcdif->base + LCDC_V8_CTRL + REG_SET); + else + writel(CTRL_INV_VS, lcdif->base + LCDC_V8_CTRL + REG_CLR); + if (bus_flags & DRM_BUS_FLAG_DE_LOW) - ctrl |= CTRL_INV_DE; - if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE) - ctrl |= CTRL_INV_PXCK; + writel(CTRL_INV_DE, lcdif->base + LCDC_V8_CTRL + REG_SET); + else + writel(CTRL_INV_DE, lcdif->base + LCDC_V8_CTRL + REG_CLR); - writel(ctrl, lcdif->base + LCDC_V8_CTRL); + if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE) + writel(CTRL_INV_PXCK, lcdif->base + LCDC_V8_CTRL + REG_SET); + else + writel(CTRL_INV_PXCK, lcdif->base + LCDC_V8_CTRL + REG_CLR); writel(DISP_SIZE_DELTA_Y(m->vdisplay) | DISP_SIZE_DELTA_X(m->hdisplay),