[U-Boot] [PATCH v2 1/3] mx6: ddr: Adjust MDREF register settings for MX6UL

[Eric Nelson]

Hi Fabio,

On 08/29/2016 11:48 AM, Eric Nelson wrote:
> Hi Fabio,
> 
> On 08/29/2016 10:56 AM, Fabio Estevam wrote:
>> From: Fabio Estevam <fabio.estevam at nxp.com>
>>
>> When running a NXP 4.1 kernel with U-Boot mainline we observe a
>> hang when going into the lowest operational point of cpufreq.
>>
>> After comparing the SPL DDR initialization against the DCD table
>> from NXP U-Boot, the key difference that causes the hang is the
>> MDREF register setting.
>>
>> In all the DDR3 MX6UL boards we have the following configuration
>> for MDREF:
>>
> 
> I think this commit message needs work.
> 
> "we have" seems to mean that the NXP U-Boot fork has this
> setting, but this isn't an explanation of why.
> 

After reviewing the manual, I think I understand why this
is needed and something like this is probably better:

	The i.MX6UL kernel uses a 32kHz clock for to drive refresh in
	low power mode. Configure the MMDC to use it as the input for
	refresh in MMDC_MDREF.

>> DATA 4 0x021B0020 0x00000800
>>
>> ,which means:
>>
>> REF_SEL = 0 -->Periodic refresh cycle: 64kHz 
>> REFR = 1 ---> Refresh Rate - 2 refreshes
>>
>> So adjust the MDREF initialization for MX6UL to fix the kernel
>> hang issue.
>>
>> Reported-by: Eric Nelson <eric at nelint.com>
>> Signed-off-by: Fabio Estevam <fabio.estevam at nxp.com>
>> ---
>> Changes since v1:
>> - Newly introduced in this version
>>
>>  arch/arm/cpu/armv7/mx6/ddr.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/cpu/armv7/mx6/ddr.c b/arch/arm/cpu/armv7/mx6/ddr.c
>> index f151eec..56d3e65 100644
>> --- a/arch/arm/cpu/armv7/mx6/ddr.c
>> +++ b/arch/arm/cpu/armv7/mx6/ddr.c
>> @@ -1183,7 +1183,7 @@ void mx6_ddr3_cfg(const struct mx6_ddr_sysinfo *sysinfo,
>>  	volatile struct mmdc_p_regs *mmdc0;
>>  	volatile struct mmdc_p_regs *mmdc1;
>>  	u32 val;
>> -	u8 tcke, tcksrx, tcksre, txpdll, taofpd, taonpd, trrd;
>> +	u8 tcke, tcksrx, tcksre, txpdll, taofpd, taonpd, trrd, refr, refsel;
>>  	u8 todtlon, taxpd, tanpd, tcwl, txp, tfaw, tcl;
>>  	u8 todt_idle_off = 0x4; /* from DDR3 Script Aid spreadsheet */
>>  	u16 trcd, trc, tras, twr, tmrd, trtp, trp, twtr, trfc, txs, txpr;
>> @@ -1472,9 +1472,15 @@ void mx6_ddr3_cfg(const struct mx6_ddr_sysinfo *sysinfo,
>>  		MMDC1(mpzqhwctrl, val);
>>
>>  	/* Step 12: Configure and activate periodic refresh */
>> -	mmdc0->mdref = (1 << 14) | /* REF_SEL: Periodic refresh cycle: 32kHz */
>> -		       (7 << 11);  /* REFR: Refresh Rate - 8 refreshes */
> 
> I'm not understanding why this is CPU specific. Is the issue
> 
>> +	if (!is_mx6ul()) {
> 
> Table 44-15 of the 6DQ reference manual says that this will generate
> tREFI at 3.9uS (256kHz).
> 

Never mind. Your comment is about the input clock, not the refresh
cycle.

I do wonder if both of these settings don't over-refresh the DDR3
though.

>> +		refsel = 1; /* REF_SEL: Periodic refresh cycle: 32kHz */
>> +		refr = 7;   /* REFR: Refresh Rate - 8 refreshes */
>> +	} else {
> 
> Table 33-15 of the 6UL manual says 7.8us (128 kHz).
> 
>> +		refsel = 0; /* REF_SEL: Periodic refresh cycle: 64kHz */
>> +		refr = 1;   /* REFR: Refresh Rate - 2 refreshes */
>> +	}
>>  
>> +	mmdc0->mdref = (refsel << 14) | (refr << 11);
>>  	/* Step 13: Deassert config request - init complete */
>>  	mmdc0->mdscr = 0x00000000;
>>  
>>
> 
> I did test this patch though, and I can confirm that the problem
> I experienced (hang with low bus frequency) goes away with just
> this change, so
> 
> Tested-by: Eric Nelson <eric at nelint.com>
>