ARM: at91: pm: fix self-refresh for sama7g5

It has been discovered that on some parts, from time to time, self-refresh
procedure doesn't work as expected. Debugging and investigating it proved
that disabling AC DLL introduce glitches in RAM controllers which
leads to unexpected behavior. This is confirmed as a hardware bug. DLL
bypass disables 3 DLLs: 2 DX DLLs and AC DLL. Thus, keep only DX DLLs
disabled. This introduce 6mA extra current consumption on VDDCORE when
switching to any ULP mode or standby mode but the self-refresh procedure
still works.

Fixes: f0bbf179 ("ARM: at91: pm: add self-refresh support for sama7g5")
Suggested-by: Frederic Schumacher <frederic.schumacher@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Tested-by: Cristian Birsan <cristian.birsan@microchip.com>
Link: https://lore.kernel.org/r/20220826083927.3107272-3-claudiu.beznea@microchip.com

arch/arm/mach-at91/pm_suspend.S

@@ -172,9 +172,15 @@ sr_ena_2:
 	/* Put DDR PHY's DLL in bypass mode for non-backup modes. */
 	cmp	r7, #AT91_PM_BACKUP
 	beq	sr_ena_3
-	ldr	tmp1, [r3, #DDR3PHY_PIR]
-	orr	tmp1, tmp1, #DDR3PHY_PIR_DLLBYP
-	str	tmp1, [r3, #DDR3PHY_PIR]
+
+	/* Disable DX DLLs. */
+	ldr	tmp1, [r3, #DDR3PHY_DX0DLLCR]
+	orr	tmp1, tmp1, #DDR3PHY_DXDLLCR_DLLDIS
+	str	tmp1, [r3, #DDR3PHY_DX0DLLCR]
+
+	ldr	tmp1, [r3, #DDR3PHY_DX1DLLCR]
+	orr	tmp1, tmp1, #DDR3PHY_DXDLLCR_DLLDIS
+	str	tmp1, [r3, #DDR3PHY_DX1DLLCR]
 
 sr_ena_3:
 	/* Power down DDR PHY data receivers. */
@@ -221,10 +227,14 @@ sr_ena_3:
 	bic	tmp1, tmp1, #DDR3PHY_DSGCR_ODTPDD_ODT0
 	str	tmp1, [r3, #DDR3PHY_DSGCR]
 
-	/* Take DDR PHY's DLL out of bypass mode. */
-	ldr	tmp1, [r3, #DDR3PHY_PIR]
-	bic	tmp1, tmp1, #DDR3PHY_PIR_DLLBYP
-	str	tmp1, [r3, #DDR3PHY_PIR]
+	/* Enable DX DLLs. */
+	ldr	tmp1, [r3, #DDR3PHY_DX0DLLCR]
+	bic	tmp1, tmp1, #DDR3PHY_DXDLLCR_DLLDIS
+	str	tmp1, [r3, #DDR3PHY_DX0DLLCR]
+
+	ldr	tmp1, [r3, #DDR3PHY_DX1DLLCR]
+	bic	tmp1, tmp1, #DDR3PHY_DXDLLCR_DLLDIS
+	str	tmp1, [r3, #DDR3PHY_DX1DLLCR]
 
 	/* Enable quasi-dynamic programming. */
 	mov	tmp1, #0

include/soc/at91/sama7-ddr.h

@@ -39,6 +39,10 @@
 
 #define DDR3PHY_ZQ0SR0				(0x188)		/* ZQ status register 0 */
 
+#define	DDR3PHY_DX0DLLCR			(0x1CC)		/* DDR3PHY DATX8 DLL Control Register */
+#define	DDR3PHY_DX1DLLCR			(0x20C)		/* DDR3PHY DATX8 DLL Control Register */
+#define		DDR3PHY_DXDLLCR_DLLDIS		(1 << 31)	/* DLL Disable */
+
 /* UDDRC */
 #define UDDRC_STAT				(0x04)		/* UDDRC Operating Mode Status Register */
 #define		UDDRC_STAT_SELFREF_TYPE_DIS	(0x0 << 4)	/* SDRAM is not in Self-refresh */