[PATCH u-boot-marvell RFC] PLEASE TEST: ddr: marvell: a38x: fix BYTE_HOMOGENEOUS_SPLIT_OUT decision

[Stefan Roese]

On 2/15/22 23:21, Chris Packham wrote:
> On Fri, Feb 11, 2022 at 5:25 AM Marek Behún <kabel at kernel.org> wrote:
>>
>> From: Marek Behún <marek.behun at nic.cz>
>>
>> In commit 3fc92a215b69 ("ddr: marvell: a38x: fix SPLIT_OUT_MIX state
>> decision") I ported a cleaned up and changed version of patch
>>    mv_ddr: a380: fix SPLIT_OUT_MIX state decision
>>
>> In the port we removed checking for BYTE_HOMOGENEOUS_SPLIT_OUT bit,
>> because:
>> - the fix seemed to work without it
>> - the bit was checked for only at one place out of two, while the second
>>    bit, BYTE_SPLIT_OUT_MIX, was checked for in both cases
>> - without the removal it didn't work on Allied Telesis' x530 board
>>
>> We recently had a chance to test on more boards, and it seems that the
>> change needs to be opposite: instead of removing the check for
>> BYTE_HOMOGENEOUS_SPLIT_OUT from the first if() statement, the check
>> needs to be added also to the second one - it needs to be at both
>> places.
>>
>> With this change all the Turris Omnia boards I have had available to
>> test seem to work, I didn't encounter not even one failed DDR training.
>>
>> As last time, I am noting that I do not understand what this code is
>> actually doing, I haven't studied the DDR training algorithm and
>> I suspect that no one will be able to explain it to U-Boot contributors,
>> so we are left with this blind poking in the code with testing whether
>> it works on several boards and hoping it doesn't break anything for
>> anyone :-(.
>>
>> Signed-off-by: Marek Behún <marek.behun at nic.cz>
> 
> Tested-by: Chris Packham <judge.packham at gmail.com>

Reviewed-by: Stefan Roese <sr at denx.de>

Thanks,
Stefan

> 
>> ---
>>   drivers/ddr/marvell/a38x/ddr3_training_centralization.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/ddr/marvell/a38x/ddr3_training_centralization.c b/drivers/ddr/marvell/a38x/ddr3_training_centralization.c
>> index 42308b6965..be9f985f22 100644
>> --- a/drivers/ddr/marvell/a38x/ddr3_training_centralization.c
>> +++ b/drivers/ddr/marvell/a38x/ddr3_training_centralization.c
>> @@ -180,7 +180,8 @@ static int ddr3_tip_centralization(u32 dev_num, u32 mode)
>>                                                                 [bit_id],
>>                                                                 EDGE_1);
>>                                          if (current_byte_status &
>> -                                           BYTE_SPLIT_OUT_MIX) {
>> +                                           (BYTE_SPLIT_OUT_MIX |
>> +                                            BYTE_HOMOGENEOUS_SPLIT_OUT)) {
>>                                                  if (cur_start_win[bit_id] >= 64)
>>                                                          cur_start_win[bit_id] -= 64;
>>                                                  else
>> @@ -197,7 +198,8 @@ static int ddr3_tip_centralization(u32 dev_num, u32 mode)
>>                                                                 EDGE_1);
>>                                          if (cur_end_win[bit_id] >= 64 &&
>>                                              (current_byte_status &
>> -                                            BYTE_SPLIT_OUT_MIX)) {
>> +                                            (BYTE_SPLIT_OUT_MIX |
>> +                                             BYTE_HOMOGENEOUS_SPLIT_OUT))) {
>>                                                  cur_end_win[bit_id] -= 64;
>>                                                  DEBUG_CENTRALIZATION_ENGINE
>>                                                          (DEBUG_LEVEL_INFO,
>> --
>> 2.34.1
>>

Viele Grüße,
Stefan Roese

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