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>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/arm/include/asm/arch-sunxi/dram.h b/arch/arm/include/asm/arch-sunxi/dram.h
index 71301db..1945f75 100644
--- a/arch/arm/include/asm/arch-sunxi/dram.h
+++ b/arch/arm/include/asm/arch-sunxi/dram.h
@@ -88,6 +88,8 @@ struct dram_para {
 	u32 emr1;
 	u32 emr2;
 	u32 emr3;
+	u32 dqs_gating_delay;
+	u32 active_windowing;
 };
 
 #define DRAM_CCR_COMMAND_RATE_1T (0x1 << 5)