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

[Marek Vasut]

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 <ma...@denx.de>
Cc: Anatolij Gustschin <ag...@denx.de>
Cc: Fabio Estevam <fabio.este...@freescale.com>
Cc: Otavio Salvador <ota...@ossystems.com.br>
Cc: Stefano Babic <sba...@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

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