[U-Boot] [RFC PATCH] arm: mx6: Clamp MMDC and DDR3 clocks for timing calculations

[Stefano Babic]

Hi Nikolay,

On 17/04/2015 00:36, Nikolay Dimitrov wrote:
> This is proposal for clamping the MMDC/DDR3 clocks to the maximum supported
> frequencies as per imx6 SOC models, and for dynamically calculating valid
> clock value based on mem_speed.
> 
> Currently the code uses impossible values for mem_speed (1333, 1600 MT/s) for
> calculating the DDR timings, and uses fixed clock (528 or 400 MHz) which
> doesn't take into account DDR3 memory limitations.
> 
> Signed-off-by: Nikolay Dimitrov <picmaster at mail.bg>
> Cc: Fabio Estevam <festevam at gmail.com>
> Cc: Stefano Babic <sbabic at denx.de>
> Cc: Tim Harvey <tharvey at gateworks.com>
> Cc: Eric Nelson <eric.nelson at boundarydevices.com>
> ---
>  arch/arm/cpu/armv7/mx6/ddr.c |   25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/cpu/armv7/mx6/ddr.c b/arch/arm/cpu/armv7/mx6/ddr.c
> index fef2231..9daa180 100644
> --- a/arch/arm/cpu/armv7/mx6/ddr.c
> +++ b/arch/arm/cpu/armv7/mx6/ddr.c
> @@ -265,7 +265,7 @@ void mx6_dram_cfg(const struct mx6_ddr_sysinfo *sysinfo,
>  	u16 tdllk = 0x1ff; /* DLL locking time: 512 cycles (JEDEC DDR3) */
>  	u8 coladdr;
>  	int clkper; /* clock period in picoseconds */
> -	int clock; /* clock freq in mHz */
> +	int clock; /* clock freq in MHz */
>  	int cs;
>  
>  	mmdc0 = (struct mmdc_p_regs *)MMDC_P0_BASE_ADDR;
> @@ -273,16 +273,31 @@ void mx6_dram_cfg(const struct mx6_ddr_sysinfo *sysinfo,
>  	mmdc1 = (struct mmdc_p_regs *)MMDC_P1_BASE_ADDR;
>  #endif
>  
> -	/* MX6D/MX6Q: 1066 MHz memory clock, clkper = 1.894ns = 1894ps */
> +	/* Limit mem_speed for MX6D/MX6Q */
>  	if (is_cpu_type(MXC_CPU_MX6Q) || is_cpu_type(MXC_CPU_MX6D)) {
> -		clock = 528;
> +		if (ddr3_cfg->mem_speed > 1066)
> +			ddr3_cfg->mem_speed = 1066; /* 1066 MT/s */
> +
>  		tcwl = 4;
>  	}
> -	/* MX6S/MX6DL: 800 MHz memory clock, clkper = 2.5ns = 2500ps */
> +	/* Limit mem_speed for MX6S/MX6DL */
>  	else {
> -		clock = 400;
> +		if (ddr3_cfg->mem_speed > 800)
> +			ddr3_cfg->mem_speed = 800;  /* 800 MT/s */
> +
>  		tcwl = 3;
>  	}
> +
> +	clock = ddr3_cfg->mem_speed / 2;
> +	/*
> +	 * Data rate of 1066 MT/s requires 533 MHz DDR3 clock, but MX6D/Q supports
> +	 * up to 528 MHz, so reduce the clock to fit chip specs
> +	 */
> +	if (is_cpu_type(MXC_CPU_MX6Q) || is_cpu_type(MXC_CPU_MX6D)) {
> +		if (clock > 528)
> +			clock = 528; /* 528 MHz */
> +	}
> +
>  	clkper = (1000 * 1000) / clock; /* pico seconds */
>  	todtlon = tcwl;
>  	taxpd = tcwl;
> 

Well done. I think we can forget the RFC of the title and apply it.

Regards,
Stefano


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