[U-Boot] [PATCH 04/11] video: Implement continuous screen refresh for SmartLCD into mxsfb

Marek Vasut
2013-07-30T21:37:54Z

The LCDIF interface doesn't give us any means to do continuous refresh
when driving a SmartLCD. To work this around, we produce a special
circular DMA descriptor, which only writes the HW_LCDIF_CTRL0 register
and sets the RUN bit.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>
---
drivers/video/mxsfb.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/drivers/video/mxsfb.c b/drivers/video/mxsfb.c
index 78709dd..98d5264 100644
--- a/drivers/video/mxsfb.c
+++ b/drivers/video/mxsfb.c
@@ -28,11 +28,14 @@
#include <asm/errno.h>
#include <asm/io.h>

+#include <asm/imx-common/dma.h>
+
#include "videomodes.h"

#define PS2KHZ(ps) (1000000000UL / (ps))

static GraphicDevice panel;
+struct mxs_dma_desc desc;

/**
* mxsfb_system_setup() - Fine-tune LCDIF configuration
@@ -207,5 +210,28 @@ void *video_hw_init(void)
/* Start framebuffer */
mxs_lcd_init(&panel, &mode, bpp);

+#ifdef CONFIG_VIDEO_MXS_MODE_SYSTEM
+ /*
+ * If the LCD runs in system mode, the LCD refresh has to be triggered
+ * manually by setting the RUN bit in HW_LCDIF_CTRL register. To avoid
+ * having to set this bit manually after every single change in the
+ * framebuffer memory, we set up specially crafted circular DMA, which
+ * sets the RUN bit, then waits until it gets cleared and repeats this
+ * infinitelly. This way, we get smooth continuous updates of the LCD.
+ */
+ struct mxs_lcdif_regs *regs = (struct mxs_lcdif_regs *)MXS_LCDIF_BASE;
+
+ memset(&desc, 0, sizeof(struct mxs_dma_desc));
+ desc.address = (dma_addr_t)&desc;
+ desc.cmd.data = MXS_DMA_DESC_COMMAND_NO_DMAXFER | MXS_DMA_DESC_CHAIN |
+ MXS_DMA_DESC_WAIT4END |
+ (1 << MXS_DMA_DESC_PIO_WORDS_OFFSET);
+ desc.cmd.pio_words[0] = readl(&regs->hw_lcdif_ctrl) | LCDIF_CTRL_RUN;
+ desc.cmd.next = (uint32_t)&desc.cmd;
+
+ /* Execute the DMA chain. */
+ mxs_dma_circ_start(MXS_DMA_CHANNEL_AHB_APBH_LCDIF, &desc);
+#endif
+
return (void *)&panel;
}
--
1.7.10.4