[PATCH v2] drm: mxsfb_crtc: Reset the eLCDIF controller

[Marek Vasut]

On 05/05/2017 04:49 PM, Fabio Estevam wrote:
> According to the eLCDIF initialization steps listed in the MX6SX
> Reference Manual the eLCDIF block reset is mandatory. 
> 
> Without performing the eLCDIF reset the display shows garbage content
> when the kernel boots.
> 
> In earlier tests this issue has not been observed because the bootloader
> was previously showing a splash screen and the bootloader display driver
> does properly implement the eLCDIF reset.
> 
> Add the eLCDIF reset to the driver, so that it can operate correctly
> independently of the bootloader.
> 
> Tested on a imx6sx-sdb board.
> 
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Fabio Estevam <fabio.estevam at nxp.com>
> ---
> Changes since v1:
> - Use readl_poll_timeout() - Marek
> - Remove unneeded comments
> 
> Marek,
> 
> As to your other suggestion, we cannot put mxsfb_reset_block() inside
> the probe function.
> 
> According to the Reference Manual the reset step is after the clock
> is enabled and prior to setting the pixel format, so the current
> location is the correct one.

I see, all right.

>  drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 43 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> index 1144e0c..69a9baf 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> @@ -35,6 +35,13 @@
>  #include "mxsfb_drv.h"
>  #include "mxsfb_regs.h"
>  
> +#define MXS_SET_ADDR		0x4
> +#define MXS_CLR_ADDR		0x8
> +#define MODULE_CLKGATE		BIT(30)
> +#define MODULE_SFTRST		BIT(31)
> +/* 1 second delay should be plenty of time for block reset */
> +#define RESET_TIMEOUT		1000000
> +
>  static u32 set_hsync_pulse_width(struct mxsfb_drm_private *mxsfb, u32 val)
>  {
>  	return (val & mxsfb->devdata->hs_wdth_mask) <<
> @@ -159,6 +166,37 @@ static void mxsfb_disable_controller(struct mxsfb_drm_private *mxsfb)
>  		clk_disable_unprepare(mxsfb->clk_disp_axi);
>  }
>  
> +/*
> + * Clear the bit and poll it cleared.  This is usually called with
> + * a reset address and mask being either SFTRST(bit 31) or CLKGATE
> + * (bit 30).
> + */
> +static int clear_poll_bit(void __iomem *addr, u32 mask)
> +{
> +	u32 reg;
> +
> +	writel(mask, addr + MXS_CLR_ADDR);
> +	udelay(1);

One last nit, is this udelay needed ?

> +	return readl_poll_timeout(addr, reg, !(reg & mask), 0, RESET_TIMEOUT);
> +}
> +
> +static int mxsfb_reset_block(void __iomem *reset_addr)
> +{
> +	int ret;
> +
> +	ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
> +	if (ret)
> +		return ret;
> +
> +	writel(MODULE_CLKGATE, reset_addr + MXS_CLR_ADDR);
> +
> +	ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
> +	if (ret)
> +		return ret;
> +
> +	return clear_poll_bit(reset_addr, MODULE_CLKGATE);
> +}
> +
>  static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
>  {
>  	struct drm_display_mode *m = &mxsfb->pipe.crtc.state->adjusted_mode;
> @@ -173,6 +211,11 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
>  	 */
>  	mxsfb_enable_axi_clk(mxsfb);
>  
> +	/* Mandatory eLCDIF reset as per the Reference Manual */
> +	err = mxsfb_reset_block(mxsfb->base);
> +	if (err)
> +		return;
> +
>  	/* Clear the FIFOs */
>  	writel(CTRL1_FIFO_CLEAR, mxsfb->base + LCDC_CTRL1 + REG_SET);
>  
> 


-- 
Best regards,
Marek Vasut