[U-Boot] [PATCH] am33xx: Stop modifying certain EMIF4D registers

[Tom Rini]

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On 11/07/2013 04:12 PM, Vaibhav Bedia wrote:
> Hi Tom,
> 
> On Thu, Nov 7, 2013 at 11:42 AM, Tom Rini <trini at ti.com> wrote:
>> Based on the definitive guide to EMIF configuration[1] certain registers
>> that we have been modifying (and are documented registers) should be
>> left in their reset values rather than modified.  This has been tested
>> on AM335x GP EVM and Beaglebone White.
>>
> 
> [...]
[snip]
>> @@ -198,11 +188,6 @@ void sdram_init(void)
>>         config_dmm(&evm_lisa_map_regs);
>>
>>  #ifdef CONFIG_TI816X_EVM_DDR2
>> -       ddr2_data.datadldiff0 = (get_cpu_rev() == 0x1 ? 0x0 : 0xF);
>> -       ddr2_ctrl.cmd0dldiff = (get_cpu_rev() == 0x1 ? 0x0 : 0xF);
>> -       ddr2_ctrl.cmd1dldiff = (get_cpu_rev() == 0x1 ? 0x0 : 0xF);
>> -       ddr2_ctrl.cmd2dldiff = (get_cpu_rev() == 0x1 ? 0x0 : 0xF);
>> -
>>         if (CONFIG_TI816X_USE_EMIF0) {
>>                 ddr2_emif0_regs.emif_ddr_phy_ctlr_1 =
>>                         (get_cpu_rev() == 0x1 ? 0x0000010B : 0x0000030B);
>> @@ -217,8 +202,6 @@ void sdram_init(void)
>>  #endif
>>
>>  #ifdef CONFIG_TI816X_EVM_DDR3
>> -       ddr3_data.datadldiff0 = (get_cpu_rev() == 0x1 ? 0x0 : 0xF);
>> -
> 
> From a quick glance it looks like at least earlier variants of TI81xx
> used these registers to work around some bugs? This might end up
> breaking those. Note that TI81xx DDR frequencies are much higher
> compared to AM335x so issues related to this might not show up
> right now.

It's an open question on if TI81xx needs these set or was simply also
setting them for historical reasons (and in turn was inherited by am335x).

- -- 
Tom
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