From fb8fa9431971b9847aafaf89281570ca41bd0b40 Mon Sep 17 00:00:00 2001 From: "Manjunathappa, Prakash" Date: Wed, 18 Jul 2012 21:03:36 +0530 Subject: [PATCH] video: da8xx-fb: configure FIFO threshold to reduce underflow errors Patch works around the below silicon errata: During LCDC initialization, there is the potential for a FIFO underflow condition to occur. A FIFO underflow condition occurs when the input FIFO is completely empty and the LCDC raster controller logic that drives data to the output pins attempts to fetch data from the FIFO. When a FIFO underflow condition occurs, incorrect data will be driven out on the LCDC data pins. Software should poll the FUF bit field in the LCD_STAT register to check if an error condition has occurred or service the interrupt if FUF_EN is enabled when FUF occurs. If the FUF bit field has been set to 1, this will indicate an underflow condition has occurred and then the software should execute a reset of the LCDC via the LPSC. This problem may occur if the LCDC FIFO threshold size (LCDDMA_CTRL[TH_FIFO_READY]) is left at its default value after reset. Increasing the FIFO threshold size will reduce or eliminate underflows. Setting the threshold size to 256 double words or larger is recommended. Above issue is described in section 2.1.3 of silicon errata http://www.ti.com/lit/er/sprz313e/sprz313e.pdf Signed-off-by: Rajashekhara, Sudhakar Signed-off-by: Manjunathappa, Prakash Signed-off-by: Florian Tobias Schandinat --- drivers/video/da8xx-fb.c | 11 +++++++---- include/video/da8xx-fb.h | 3 +++ 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/video/da8xx-fb.c b/drivers/video/da8xx-fb.c index 6b7f2da6f907..6f0fb2d50c28 100644 --- a/drivers/video/da8xx-fb.c +++ b/drivers/video/da8xx-fb.c @@ -353,8 +353,8 @@ static void lcd_blit(int load_mode, struct da8xx_fb_par *par) lcd_enable_raster(); } -/* Configure the Burst Size of DMA */ -static int lcd_cfg_dma(int burst_size) +/* Configure the Burst Size and fifo threhold of DMA */ +static int lcd_cfg_dma(int burst_size, int fifo_th) { u32 reg; @@ -378,6 +378,9 @@ static int lcd_cfg_dma(int burst_size) default: return -EINVAL; } + + reg |= (fifo_th << 8); + lcdc_write(reg, LCD_DMA_CTRL_REG); return 0; @@ -679,8 +682,8 @@ static int lcd_init(struct da8xx_fb_par *par, const struct lcd_ctrl_config *cfg, lcdc_write((lcdc_read(LCD_RASTER_TIMING_2_REG) & ~LCD_INVERT_PIXEL_CLOCK), LCD_RASTER_TIMING_2_REG); - /* Configure the DMA burst size. */ - ret = lcd_cfg_dma(cfg->dma_burst_sz); + /* Configure the DMA burst size and fifo threshold. */ + ret = lcd_cfg_dma(cfg->dma_burst_sz, cfg->fifo_th); if (ret < 0) return ret; diff --git a/include/video/da8xx-fb.h b/include/video/da8xx-fb.h index 89d43b3d4cb9..5a0e4f9efb53 100644 --- a/include/video/da8xx-fb.h +++ b/include/video/da8xx-fb.h @@ -82,6 +82,9 @@ struct lcd_ctrl_config { /* Raster Data Order Select: 1=Most-to-least 0=Least-to-most */ unsigned char raster_order; + + /* DMA FIFO threshold */ + int fifo_th; }; struct lcd_sync_arg { -- 2.30.2