OMAP4+: Force DDR in self-refresh after warm reset

OMAP4+: Force DDR in self-refresh after warm reset

Errata ID:i727

Description: The refresh rate is programmed in the EMIF_SDRAM_REF_CTRL[15:0]
REG_REFRESH_RATE parameter taking into account frequency of the device.
When a warm reset is applied on the system, the OMAP processor restarts
with another OPP and so frequency is not the same. Due to this frequency
change, the refresh rate will be too low and could result in an unexpected
behavior on the memory side.

Workaround:
The workaround is to force self-refresh when coming back from the warm reset
with the following sequence:
• Set EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE to 0x2
• Set EMIF_PWR_MGMT_CTRL[7:4] REG_SR_TIM to 0x0
• Do a dummy read (loads automatically new value of sr_tim)
This will reduce the risk of memory content corruption, but memory content
can't be guaranteed after a warm reset.

This errata is impacted on
OMAP4430: 1.0, 2.0, 2.1, 2.2, 2.3
OMAP4460: 1.0, 1.1
OMAP4470: 1.0
OMAP5430: 1.0

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Senthilvadivu Guruswamy <svadivu@ti.com>