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

[Sergei Shtylyov <sshtylyov@mvista.com>]

Hello.

On 11-07-2012 19:14, 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>
> ---
>   drivers/video/da8xx-fb.c |   15 +++++++++++----
>   include/video/da8xx-fb.h |    3 +++
>   2 files changed, 14 insertions(+), 4 deletions(-)

> diff --git a/drivers/video/da8xx-fb.c b/drivers/video/da8xx-fb.c
> index 47118c7..2010dd7 100644
> --- a/drivers/video/da8xx-fb.c
> +++ b/drivers/video/da8xx-fb.c
> @@ -344,8 +344,8 @@ 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)

    One space too much.

>   {
>   	u32 reg;
>
> @@ -719,8 +722,10 @@ static irqreturn_t lcdc_irq_handler_rev02(int irq, void *arg)
>
>   	if ((stat & LCD_SYNC_LOST) && (stat & LCD_FIFO_UNDERFLOW)) {
>   		lcd_disable_raster();
> +		clk_disable(par->lcdc_clk);
>   		lcdc_write(stat, LCD_MASKED_STAT_REG);

    Will LCDC register wrtite work without LCDC clock?

>   		lcd_enable_raster();
> +		clk_enable(par->lcdc_clk);
>   	} else if (stat & LCD_PL_LOAD_DONE) {
>   		/*
>   		 * Must disable raster before changing state of any control bit.
> @@ -774,8 +779,10 @@ static irqreturn_t lcdc_irq_handler_rev01(int irq, void *arg)
>
>   	if ((stat & LCD_SYNC_LOST) && (stat & LCD_FIFO_UNDERFLOW)) {
>   		lcd_disable_raster();
> +		clk_disable(par->lcdc_clk);
>   		lcdc_write(stat, LCD_STAT_REG);

    Same question.

WBR, Sergei