Subject: [PATCH] ARM: imx6: Fix procedure to switch the parent of LDB_DI_CLK

From: [email-masked] (Dirk Behme)
Date: Wed, 04 Jun 2014 18:37:23 +0200

On 09.04.2014 13:55, Fabio Estevam wrote:
> From: Fabio Estevam <[email-masked]>
>
> Due to incorrect placement of the clock gate cell in the ldb_di[x]_clk tree,
> the glitchy parent mux of ldb_di[x]_clk can cause a glitch to enter the
> ldb_di_ipu_div divider. If the divider gets locked up, no ldb_di[x]_clk is
> generated, and the LVDS display will hang when the ipu_di_clk is sourced from
> ldb_di_clk.
>
> To fix the problem, both the new and current parent of the ldb_di_clk should
> be disabled before the switch. This patch ensures that correct steps are
> followed when ldb_di_clk parent is switched in the beginning of boot.
>
> Signed-off-by: Ranjani Vaidyanathan <[email-masked]>
> Signed-off-by: Fabio Estevam <[email-masked]>
> ---
>   arch/arm/mach-imx/clk-imx6q.c | 125 ++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 121 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/mach-imx/clk-imx6q.c b/arch/arm/mach-imx/clk-imx6q.c
> index 20ad0d1..3ee45f4 100644
> --- a/arch/arm/mach-imx/clk-imx6q.c
> +++ b/arch/arm/mach-imx/clk-imx6q.c
....
> +static void disable_anatop_clocks(void __iomem *anatop_base)
> +{
> +	unsigned int reg;
> +
> +	/* Make sure PFDs are disabled at boot. */
> +	reg = readl_relaxed(anatop_base + 0x100);
> +	/* Cannot disable pll2_pfd2_396M, as it is the MMDC clock in iMX6DL */
> +	if (cpu_is_imx6dl())
> +		reg |= 0x80008080;
> +	else
> +		reg |= 0x80808080;

There are two issues with this code section:

1) You want to know here if pll2_pfd2_396M is used as MMDC clock. This 
is independent of IMX6DL. Even a Quad/Dual could use pll2_pfd2_396M as 
MMDC clock. You better should check what you are really looking for:

if (MMDC clock == pll2_pfd2_396M)
...

2) Why is bit 31, i.e. the uppermost '8' in 0x80808080, set here? It 
looks like the TRM marks bit 31 - 24 as reserved?

Best regards

Dirk