tree 95fc1f67b4c7d5486b0dbe93e65d3a753350408e
parent c4f0aa544a4f4c884eeab24529a3f51cc343bc33
author Siarhei Siamashka <siarhei.siamashka@gmail.com> 1407033171 +0300
committer Hans de Goede <hdegoede@redhat.com> 1407825753 +0200

sunxi: dram: Configurable DQS gating window mode and delay

The hardware DQS gate training is a bit unreliable and does not
always find the best delay settings.

So we introduce a 32-bit 'dqs_gating_delay' variable, where each
byte encodes the DQS gating delay for each byte lane. The delay
granularity is 1/4 cycle.

Also we allow to enable the active DQS gating window mode, which
works better than the passive mode in practice. The DDR3 spec
says that there is a 0.9 cycles preamble and 0.3 cycle postamble.
The DQS window has to be opened during preamble and closed during
postamble. In the passive window mode, the gating window is opened
and closed by just using the gating delay settings. And because
of the 1/4 cycle delay granularity, accurately hitting the 0.3
cycle long postamble is a bit tough. In the active window mode,
the gating window is auto-closing with the help of monitoring
the DQS line, which relaxes the gating delay accuracy requirements.

But the hardware DQS gate training is still performed in the passive
window mode. It is a more strict test, which is reducing the results
variance compared to the training with active window mode.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>