fbdev: da8xx/omap-l1xx: implement double buffering

This work includes the following:

- Implement handler for FBIO_WAITFORVSYNC ioctl.

- Allocate the data and palette buffers separately. A consequence of
this is that the palette and data loading is now done in different
phases. And that the LCD must be disabled temporarily after the palette
is loaded but this will only happen once after init and each time the
palette is changed. I think this is OK.

- Allocate two (ping and pong) framebuffers from memory.

- Add pan_display handler which toggles the LCDC DMA registers between
the ping and pong buffers.

Signed-off-by: Martin Ambrose <[e-mail]>
Cc: Chaithrika U S <[e-mail]>
Cc: Sudhakar Rajashekhara <[e-mail]>
Cc: Krzysztof Helt <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/video/da8xx-fb.c

···
 #define DRIVER_NAME "da8xx_lcdc"
 
 /* LCD Status Register */
+#define LCD_END_OF_FRAME1		BIT(9)
 #define LCD_END_OF_FRAME0		BIT(8)
+#define LCD_PL_LOAD_DONE		BIT(6)
 #define LCD_FIFO_UNDERFLOW		BIT(5)
 #define LCD_SYNC_LOST			BIT(2)
 
···
 #define LCD_PALETTE_LOAD_MODE(x)	((x) << 20)
 #define PALETTE_AND_DATA		0x00
 #define PALETTE_ONLY			0x01
+#define DATA_ONLY			0x02
 
 #define LCD_MONO_8BIT_MODE		BIT(9)
 #define LCD_RASTER_ORDER		BIT(8)
 #define LCD_TFT_MODE			BIT(7)
 #define LCD_UNDERFLOW_INT_ENA		BIT(6)
+#define LCD_PL_ENABLE			BIT(4)
 #define LCD_MONOCHROME_MODE		BIT(1)
 #define LCD_RASTER_ENABLE		BIT(0)
 #define LCD_TFT_ALT_ENABLE		BIT(23)
···
 #define  LCD_DMA_CTRL_REG			0x40
 #define  LCD_DMA_FRM_BUF_BASE_ADDR_0_REG	0x44
 #define  LCD_DMA_FRM_BUF_CEILING_ADDR_0_REG	0x48
+#define  LCD_DMA_FRM_BUF_BASE_ADDR_1_REG	0x4C
+#define  LCD_DMA_FRM_BUF_CEILING_ADDR_1_REG	0x50
+
+#define LCD_NUM_BUFFERS	2
 
 #define WSI_TIMEOUT	50
 #define PALETTE_SIZE	256
···
 struct da8xx_fb_par {
 	resource_size_t p_palette_base;
 	unsigned char *v_palette_base;
+	dma_addr_t		vram_phys;
+	unsigned long		vram_size;
+	void			*vram_virt;
+	unsigned int		dma_start;
+	unsigned int		dma_end;
 	struct clk *lcdc_clk;
 	int irq;
 	unsigned short pseudo_palette[16];
-	unsigned int databuf_sz;
 	unsigned int palette_sz;
 	unsigned int pxl_clk;
 	int blank;
+	wait_queue_head_t	vsync_wait;
+	int			vsync_flag;
+	int			vsync_timeout;
 #ifdef CONFIG_CPU_FREQ
 	struct notifier_block	freq_transition;
 #endif
···
 	.type = FB_TYPE_PACKED_PIXELS,
 	.type_aux = 0,
 	.visual = FB_VISUAL_PSEUDOCOLOR,
-	.xpanstep = 1,
+	.xpanstep = 0,
 	.ypanstep = 1,
-	.ywrapstep = 1,
+	.ywrapstep = 0,
 	.accel = FB_ACCEL_NONE
 };
 
···
 
 static void lcd_blit(int load_mode, struct da8xx_fb_par *par)
 {
-	u32 tmp = par->p_palette_base + par->databuf_sz - 4;
-	u32 reg;
+	u32 start;
+	u32 end;
+	u32 reg_ras;
+	u32 reg_dma;
 
-	/* Update the databuf in the hw. */
-	lcdc_write(par->p_palette_base, LCD_DMA_FRM_BUF_BASE_ADDR_0_REG);
-	lcdc_write(tmp, LCD_DMA_FRM_BUF_CEILING_ADDR_0_REG);
+	/* init reg to clear PLM (loading mode) fields */
+	reg_ras = lcdc_read(LCD_RASTER_CTRL_REG);
+	reg_ras &= ~(3 << 20);
 
-	/* Start the DMA. */
-	reg = lcdc_read(LCD_RASTER_CTRL_REG);
-	reg &= ~(3 << 20);
-	if (load_mode == LOAD_DATA)
-		reg |= LCD_PALETTE_LOAD_MODE(PALETTE_AND_DATA);
-	else if (load_mode == LOAD_PALETTE)
-		reg |= LCD_PALETTE_LOAD_MODE(PALETTE_ONLY);
+	reg_dma  = lcdc_read(LCD_DMA_CTRL_REG);
 
-	lcdc_write(reg, LCD_RASTER_CTRL_REG);
+	if (load_mode == LOAD_DATA) {
+		start    = par->dma_start;
+		end      = par->dma_end;
+
+		reg_ras |= LCD_PALETTE_LOAD_MODE(DATA_ONLY);
+		reg_dma |= LCD_END_OF_FRAME_INT_ENA;
+		reg_dma |= LCD_DUAL_FRAME_BUFFER_ENABLE;
+
+		lcdc_write(start, LCD_DMA_FRM_BUF_BASE_ADDR_0_REG);
+		lcdc_write(end, LCD_DMA_FRM_BUF_CEILING_ADDR_0_REG);
+		lcdc_write(start, LCD_DMA_FRM_BUF_BASE_ADDR_1_REG);
+		lcdc_write(end, LCD_DMA_FRM_BUF_CEILING_ADDR_1_REG);
+	} else if (load_mode == LOAD_PALETTE) {
+		start    = par->p_palette_base;
+		end      = start + par->palette_sz - 1;
+
+		reg_ras |= LCD_PALETTE_LOAD_MODE(PALETTE_ONLY);
+		reg_ras |= LCD_PL_ENABLE;
+
+		lcdc_write(start, LCD_DMA_FRM_BUF_BASE_ADDR_0_REG);
+		lcdc_write(end, LCD_DMA_FRM_BUF_CEILING_ADDR_0_REG);
+	}
+
+	lcdc_write(reg_dma, LCD_DMA_CTRL_REG);
+	lcdc_write(reg_ras, LCD_RASTER_CTRL_REG);
+
+	/*
+	 * The Raster enable bit must be set after all other control fields are
+	 * set.
+	 */
+	lcd_enable_raster();
 }
 
 /* Configure the Burst Size of DMA */
···
 static int lcd_cfg_frame_buffer(struct da8xx_fb_par *par, u32 width, u32 height,
 		u32 bpp, u32 raster_order)
 {
-	u32 bpl, reg;
+	u32 reg;
 
-	/* Disable Dual Frame Buffer. */
-	reg = lcdc_read(LCD_DMA_CTRL_REG);
-	lcdc_write(reg & ~LCD_DUAL_FRAME_BUFFER_ENABLE,
-						LCD_DMA_CTRL_REG);
 	/* Set the Panel Width */
 	/* Pixels per line = (PPL + 1)*16 */
 	/*0x3F in bits 4..9 gives max horisontal resolution = 1024 pixels*/
···
 		return -EINVAL;
 	}
 
-	bpl = width * bpp / 8;
-	par->databuf_sz = height * bpl + par->palette_sz;
-
 	return 0;
 }
 
···
 			      struct fb_info *info)
 {
 	struct da8xx_fb_par *par = info->par;
-	unsigned short *palette = (unsigned short *)par->v_palette_base;
+	unsigned short *palette = (unsigned short *) par->v_palette_base;
 	u_short pal;
+	int update_hw = 0;
 
 	if (regno > 255)
 		return 1;
···
 		pal |= (green & 0x00f0);
 		pal |= (blue & 0x000f);
 
-		palette[regno] = pal;
-
+		if (palette[regno] != pal) {
+			update_hw = 1;
+			palette[regno] = pal;
+		}
 	} else if ((info->var.bits_per_pixel == 16) && regno < 16) {
 		red >>= (16 - info->var.red.length);
 		red <<= info->var.red.offset;
···
 
 		par->pseudo_palette[regno] = red | green | blue;
 
-		palette[0] = 0x4000;
+		if (palette[0] != 0x4000) {
+			update_hw = 1;
+			palette[0] = 0x4000;
+		}
 	}
+
+	/* Update the palette in the h/w as needed. */
+	if (update_hw)
+		lcd_blit(LOAD_PALETTE, par);
 
 	return 0;
 }
···
 
 static irqreturn_t lcdc_irq_handler(int irq, void *arg)
 {
+	struct da8xx_fb_par *par = arg;
 	u32 stat = lcdc_read(LCD_STAT_REG);
+	u32 reg_ras;
 
 	if ((stat & LCD_SYNC_LOST) && (stat & LCD_FIFO_UNDERFLOW)) {
 		lcd_disable_raster();
 		lcdc_write(stat, LCD_STAT_REG);
 		lcd_enable_raster();
-	} else
+	} else if (stat & LCD_PL_LOAD_DONE) {
+		/*
+		 * Must disable raster before changing state of any control bit.
+		 * And also must be disabled before clearing the PL loading
+		 * interrupt via the following write to the status register. If
+		 * this is done after then one gets multiple PL done interrupts.
+		 */
+		lcd_disable_raster();
+
 		lcdc_write(stat, LCD_STAT_REG);
+
+		/* Disable PL completion inerrupt */
+		reg_ras  = lcdc_read(LCD_RASTER_CTRL_REG);
+		reg_ras &= ~LCD_PL_ENABLE;
+		lcdc_write(reg_ras, LCD_RASTER_CTRL_REG);
+
+		/* Setup and start data loading mode */
+		lcd_blit(LOAD_DATA, par);
+	} else {
+		lcdc_write(stat, LCD_STAT_REG);
+
+		if (stat & LCD_END_OF_FRAME0) {
+			lcdc_write(par->dma_start,
+				   LCD_DMA_FRM_BUF_BASE_ADDR_0_REG);
+			lcdc_write(par->dma_end,
+				   LCD_DMA_FRM_BUF_CEILING_ADDR_0_REG);
+			par->vsync_flag = 1;
+			wake_up_interruptible(&par->vsync_wait);
+		}
+
+		if (stat & LCD_END_OF_FRAME1) {
+			lcdc_write(par->dma_start,
+				   LCD_DMA_FRM_BUF_BASE_ADDR_1_REG);
+			lcdc_write(par->dma_end,
+				   LCD_DMA_FRM_BUF_CEILING_ADDR_1_REG);
+			par->vsync_flag = 1;
+			wake_up_interruptible(&par->vsync_wait);
+		}
+	}
 
 	return IRQ_HANDLED;
 }
···
 
 		unregister_framebuffer(info);
 		fb_dealloc_cmap(&info->cmap);
-		dma_free_coherent(NULL, par->databuf_sz + PAGE_SIZE,
-					info->screen_base - PAGE_SIZE,
-					info->fix.smem_start);
+		dma_free_coherent(NULL, PALETTE_SIZE, par->v_palette_base,
+				  par->p_palette_base);
+		dma_free_coherent(NULL, par->vram_size, par->vram_virt,
+				  par->vram_phys);
 		free_irq(par->irq, par);
 		clk_disable(par->lcdc_clk);
 		clk_put(par->lcdc_clk);
···
 		release_mem_region(lcdc_regs->start, resource_size(lcdc_regs));
 
 	}
+	return 0;
+}
+
+/*
+ * Function to wait for vertical sync which for this LCD peripheral
+ * translates into waiting for the current raster frame to complete.
+ */
+static int fb_wait_for_vsync(struct fb_info *info)
+{
+	struct da8xx_fb_par *par = info->par;
+	int ret;
+
+	/*
+	 * Set flag to 0 and wait for isr to set to 1. It would seem there is a
+	 * race condition here where the ISR could have occured just before or
+	 * just after this set. But since we are just coarsely waiting for
+	 * a frame to complete then that's OK. i.e. if the frame completed
+	 * just before this code executed then we have to wait another full
+	 * frame time but there is no way to avoid such a situation. On the
+	 * other hand if the frame completed just after then we don't need
+	 * to wait long at all. Either way we are guaranteed to return to the
+	 * user immediately after a frame completion which is all that is
+	 * required.
+	 */
+	par->vsync_flag = 0;
+	ret = wait_event_interruptible_timeout(par->vsync_wait,
+					       par->vsync_flag != 0,
+					       par->vsync_timeout);
+	if (ret < 0)
+		return ret;
+	if (ret == 0)
+		return -ETIMEDOUT;
+
 	return 0;
 }
 
···
 					sync_arg.pulse_width,
 					sync_arg.front_porch);
 		break;
+	case FBIO_WAITFORVSYNC:
+		return fb_wait_for_vsync(info);
 	default:
 		return -EINVAL;
 	}
···
 	return ret;
 }
 
+/*
+ * Set new x,y offsets in the virtual display for the visible area and switch
+ * to the new mode.
+ */
+static int da8xx_pan_display(struct fb_var_screeninfo *var,
+			     struct fb_info *fbi)
+{
+	int ret = 0;
+	struct fb_var_screeninfo new_var;
+	struct da8xx_fb_par         *par = fbi->par;
+	struct fb_fix_screeninfo    *fix = &fbi->fix;
+	unsigned int end;
+	unsigned int start;
+
+	if (var->xoffset != fbi->var.xoffset ||
+			var->yoffset != fbi->var.yoffset) {
+		memcpy(&new_var, &fbi->var, sizeof(new_var));
+		new_var.xoffset = var->xoffset;
+		new_var.yoffset = var->yoffset;
+		if (fb_check_var(&new_var, fbi))
+			ret = -EINVAL;
+		else {
+			memcpy(&fbi->var, &new_var, sizeof(new_var));
+
+			start	= fix->smem_start +
+				new_var.yoffset * fix->line_length +
+				new_var.xoffset * var->bits_per_pixel / 8;
+			end	= start + var->yres * fix->line_length - 1;
+			par->dma_start	= start;
+			par->dma_end	= end;
+		}
+	}
+
+	return ret;
+}
+
 static struct fb_ops da8xx_fb_ops = {
 	.owner = THIS_MODULE,
 	.fb_check_var = fb_check_var,
 	.fb_setcolreg = fb_setcolreg,
+	.fb_pan_display = da8xx_pan_display,
 	.fb_ioctl = fb_ioctl,
 	.fb_fillrect = cfb_fillrect,
 	.fb_copyarea = cfb_copyarea,
···
 	}
 
 	/* allocate frame buffer */
-	da8xx_fb_info->screen_base = dma_alloc_coherent(NULL,
-					par->databuf_sz + PAGE_SIZE,
-					(resource_size_t *)
-					&da8xx_fb_info->fix.smem_start,
-					GFP_KERNEL | GFP_DMA);
+	par->vram_size = lcdc_info->width * lcdc_info->height * lcd_cfg->bpp;
+	par->vram_size = PAGE_ALIGN(par->vram_size/8);
+	par->vram_size = par->vram_size * LCD_NUM_BUFFERS;
 
-	if (!da8xx_fb_info->screen_base) {
+	par->vram_virt = dma_alloc_coherent(NULL,
+					    par->vram_size,
+					    (resource_size_t *) &par->vram_phys,
+					    GFP_KERNEL | GFP_DMA);
+	if (!par->vram_virt) {
 		dev_err(&device->dev,
 			"GLCD: kmalloc for frame buffer failed\n");
 		ret = -EINVAL;
 		goto err_release_fb;
 	}
 
-	/* move palette base pointer by (PAGE_SIZE - palette_sz) bytes */
-	par->v_palette_base = da8xx_fb_info->screen_base +
-				(PAGE_SIZE - par->palette_sz);
-	par->p_palette_base = da8xx_fb_info->fix.smem_start +
-				(PAGE_SIZE - par->palette_sz);
+	da8xx_fb_info->screen_base = (char __iomem *) par->vram_virt;
+	da8xx_fb_fix.smem_start    = par->vram_phys;
+	da8xx_fb_fix.smem_len      = par->vram_size;
+	da8xx_fb_fix.line_length   = (lcdc_info->width * lcd_cfg->bpp) / 8;
 
-	/* the rest of the frame buffer is pixel data */
-	da8xx_fb_info->screen_base = par->v_palette_base + par->palette_sz;
-	da8xx_fb_fix.smem_start = par->p_palette_base + par->palette_sz;
-	da8xx_fb_fix.smem_len = par->databuf_sz - par->palette_sz;
-	da8xx_fb_fix.line_length = (lcdc_info->width * lcd_cfg->bpp) / 8;
+	par->dma_start = par->vram_phys;
+	par->dma_end   = par->dma_start + lcdc_info->height *
+		da8xx_fb_fix.line_length - 1;
+
+	/* allocate palette buffer */
+	par->v_palette_base = dma_alloc_coherent(NULL,
+					       PALETTE_SIZE,
+					       (resource_size_t *)
+					       &par->p_palette_base,
+					       GFP_KERNEL | GFP_DMA);
+	if (!par->v_palette_base) {
+		dev_err(&device->dev,
+			"GLCD: kmalloc for palette buffer failed\n");
+		ret = -EINVAL;
+		goto err_release_fb_mem;
+	}
+	memset(par->v_palette_base, 0, PALETTE_SIZE);
 
 	par->irq = platform_get_irq(device, 0);
 	if (par->irq < 0) {
 		ret = -ENOENT;
-		goto err_release_fb_mem;
+		goto err_release_pl_mem;
 	}
 
 	ret = request_irq(par->irq, lcdc_irq_handler, 0, DRIVER_NAME, par);
 	if (ret)
-		goto err_release_fb_mem;
+		goto err_release_pl_mem;
 
 	/* Initialize par */
 	da8xx_fb_info->var.bits_per_pixel = lcd_cfg->bpp;
···
 	da8xx_fb_var.xres = lcdc_info->width;
 	da8xx_fb_var.xres_virtual = lcdc_info->width;
 
-	da8xx_fb_var.yres = lcdc_info->height;
-	da8xx_fb_var.yres_virtual = lcdc_info->height;
+	da8xx_fb_var.yres         = lcdc_info->height;
+	da8xx_fb_var.yres_virtual = lcdc_info->height * LCD_NUM_BUFFERS;
 
 	da8xx_fb_var.grayscale =
 	    lcd_cfg->p_disp_panel->panel_shade == MONOCHROME ? 1 : 0;
···
 	ret = fb_alloc_cmap(&da8xx_fb_info->cmap, PALETTE_SIZE, 0);
 	if (ret)
 		goto err_free_irq;
-
-	/* First palette_sz byte of the frame buffer is the palette */
 	da8xx_fb_info->cmap.len = par->palette_sz;
-
-	/* Flush the buffer to the screen. */
-	lcd_blit(LOAD_DATA, par);
 
 	/* initialize var_screeninfo */
 	da8xx_fb_var.activate = FB_ACTIVATE_FORCE;
 	fb_set_var(da8xx_fb_info, &da8xx_fb_var);
 
 	dev_set_drvdata(&device->dev, da8xx_fb_info);
+
+	/* initialize the vsync wait queue */
+	init_waitqueue_head(&par->vsync_wait);
+	par->vsync_timeout = HZ / 5;
+
 	/* Register the Frame Buffer  */
 	if (register_framebuffer(da8xx_fb_info) < 0) {
 		dev_err(&device->dev,
···
 		goto err_cpu_freq;
 	}
 #endif
-
-	/* enable raster engine */
-	lcd_enable_raster();
-
 	return 0;
 
 #ifdef CONFIG_CPU_FREQ
···
 err_free_irq:
 	free_irq(par->irq, par);
 
+err_release_pl_mem:
+	dma_free_coherent(NULL, PALETTE_SIZE, par->v_palette_base,
+			  par->p_palette_base);
+
 err_release_fb_mem:
-	dma_free_coherent(NULL, par->databuf_sz + PAGE_SIZE,
-				da8xx_fb_info->screen_base - PAGE_SIZE,
-				da8xx_fb_info->fix.smem_start);
+	dma_free_coherent(NULL, par->vram_size, par->vram_virt, par->vram_phys);
 
 err_release_fb:
 	framebuffer_release(da8xx_fb_info);

include/video/da8xx-fb.h

···
 #define FBIPUT_COLOR		_IOW('F', 6, int)
 #define FBIPUT_HSYNC		_IOW('F', 9, int)
 #define FBIPUT_VSYNC		_IOW('F', 10, int)
+#define FBIO_WAITFORVSYNC	_IOW('F', 0x20, u_int32_t)
 
 #endif  /* ifndef DA8XX_FB_H */