Re: [PATCH v2 1/2] video: da8xx-fb: configure FIFO threshold to reduce underflow errors

[Florian Tobias Schandinat <FlorianSchandinat@gmx.de>]

On 07/18/2012 03:33 PM, Manjunathappa, Prakash wrote:
> 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 <sudhakar.raj@ti.com>
> Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>

Applied both patches of this series.


Thanks,

Florian Tobias Schandinat

> ---
> Seems like version 1 of this patch did not reach fbdev mailing list.
> Since v1:
> Removed clk_disable/clk_enable from error interrupt handling code.
> 
>  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 183366d..186ab5a 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 89d43b3..5a0e4f9 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 {