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

[Nikolay Dimitrov]

Hi Stefano,

On 04/22/2015 03:12 PM, Stefano Babic wrote:
> 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.

Do you need me to reword the commit message?

Regards,
Nikolay