[PATCH] ARM: at91: pm: cpu_idle: switch DDR to power-down mode

[Nicolas Ferre <nicolas.ferre@microchip.com>]

On some DDR controllers, compatible with the sama5d3 one,
the sequence to enter/exit/re-enter the self-refresh mode adds
more constrains than what is currently written in the at91_idle
driver. An actual access to the DDR chip is needed between exit
and re-enter of this mode which is somehow difficult to implement.
This sequence can completely hang the SoC. It is particularly
experienced on parts which embed a L2 cache if the code run
between IDLE calls fits in it...

Moreover, as the intention is to enter and exit pretty rapidly
from IDLE, the power-down mode is a good candidate.

So now we use power-down instead of self-refresh. As we can
simplify the funciton for sama5d3 compatible DDR controllers,
we instanciate a new sama5d3_ddr_standby() function.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
---
 arch/arm/mach-at91/pm.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c
index 3d89b7905bd9..63e7df8ec815 100644
--- a/arch/arm/mach-at91/pm.c
+++ b/arch/arm/mach-at91/pm.c
@@ -289,6 +289,23 @@ static void at91_ddr_standby(void)
 		at91_ramc_write(1, AT91_DDRSDRC_LPR, saved_lpr1);
 }
 
+static void sama5d3_ddr_standby(void)
+{
+	u32 lpr0;
+	u32 saved_lpr0;
+
+	saved_lpr0 = at91_ramc_read(0, AT91_DDRSDRC_LPR);
+	lpr0 = saved_lpr0 & ~AT91_DDRSDRC_LPCB;
+	lpr0 |= AT91_DDRSDRC_LPCB_POWER_DOWN;
+
+	/* self-refresh mode now */
+	at91_ramc_write(0, AT91_DDRSDRC_LPR, lpr0);
+
+	cpu_do_idle();
+
+	at91_ramc_write(0, AT91_DDRSDRC_LPR, saved_lpr0);
+}
+
 /* We manage both DDRAM/SDRAM controllers, we need more than one value to
  * remember.
  */
@@ -323,7 +340,7 @@ static const struct of_device_id const ramc_ids[] __initconst = {
 	{ .compatible = "atmel,at91rm9200-sdramc", .data = at91rm9200_standby },
 	{ .compatible = "atmel,at91sam9260-sdramc", .data = at91sam9_sdram_standby },
 	{ .compatible = "atmel,at91sam9g45-ddramc", .data = at91_ddr_standby },
-	{ .compatible = "atmel,sama5d3-ddramc", .data = at91_ddr_standby },
+	{ .compatible = "atmel,sama5d3-ddramc", .data = sama5d3_ddr_standby },
 	{ /*sentinel*/ }
 };
 
-- 
2.9.0