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

Ranjani.Vaidyanathan at freescale.com Ranjani.Vaidyanathan at freescale.com
Wed Jun 4 10:29:58 PDT 2014

Hi Dirk,

Responses below.


-----Original Message-----
From: Dirk Behme [mailto:dirk.behme at gmail.com] 
Sent: Wednesday, June 04, 2014 11:37 AM
To: Vaidyanathan Ranjani-RA5478; Estevam Fabio-R49496
Cc: Fabio Estevam; Guo Shawn-R65073; christian.gmeiner at gmail.com; linux-arm-kernel at lists.infradead.org
Subject: Re: [PATCH] ARM: imx6: Fix procedure to switch the parent of LDB_DI_CLK

On 09.04.2014 13:55, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam at freescale.com>
> 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 
> <Ranjani.Vaidyanathan at freescale.com>
> Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
> ---
>   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)
[RV] Yes, you are perfectly correct. We need to check MMDC parent clock. 

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?
[RV] Yes, this should also be fixed. 

Best regards


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