ARM: at91: pm: change BU Power Switch to automatic mode

[ Upstream commit 6fc5bdfa872b7da51b5507a1327a17c3db2fcf95 ]

Change how the Backup Unit Power is configured and force the
automatic/hardware mode.
This change eliminates the need for software management of the power
switch, ensuring it transitions to the backup power source before
entering low power modes.

This is done in the only location where this switch was configured. It's
usually done in the bootloader.

Previously, the loss of the VDDANA (or VDDIN33) power source was not
automatically compensated by an alternative power source. This resulted
in the loss of Backup Unit content, including Backup Self-refresh low
power mode information, OTP emulation configuration, and boot
configuration, for instance.

Fixes: ac809e7879b1 ("ARM: at91: pm: switch backup area to vbat in backup mode")
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20241125165648.509162-1-nicolas.ferre@microchip.com
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c
index c8cc993ca8ca13ddda3dc109c1ad2c844da94972..91efc3d4de61d80ffb2678e03f71810098b10b06 100644 (file)
--- a/arch/arm/mach-at91/pm.c
+++ b/arch/arm/mach-at91/pm.c
@@ -403,7 +403,21 @@ static int at91_suspend_finish(unsigned long val)
        return 0;
 }
 
-static void at91_pm_switch_ba_to_vbat(void)
+/**
+ * at91_pm_switch_ba_to_auto() - Configure Backup Unit Power Switch
+ * to automatic/hardware mode.
+ *
+ * The Backup Unit Power Switch can be managed either by software or hardware.
+ * Enabling hardware mode allows the automatic transition of power between
+ * VDDANA (or VDDIN33) and VDDBU (or VBAT, respectively), based on the
+ * availability of these power sources.
+ *
+ * If the Backup Unit Power Switch is already in automatic mode, no action is
+ * required. If it is in software-controlled mode, it is switched to automatic
+ * mode to enhance safety and eliminate the need for toggling between power
+ * sources.
+ */
+static void at91_pm_switch_ba_to_auto(void)
 {
        unsigned int offset = offsetof(struct at91_pm_sfrbu_regs, pswbu);
        unsigned int val;
@@ -414,24 +428,19 @@ static void at91_pm_switch_ba_to_vbat(void)
 
        val = readl(soc_pm.data.sfrbu + offset);
 
-       /* Already on VBAT. */
-       if (!(val & soc_pm.sfrbu_regs.pswbu.state))
+       /* Already on auto/hardware. */
+       if (!(val & soc_pm.sfrbu_regs.pswbu.ctrl))
                return;
 
-       val &= ~soc_pm.sfrbu_regs.pswbu.softsw;
-       val |= soc_pm.sfrbu_regs.pswbu.key | soc_pm.sfrbu_regs.pswbu.ctrl;
+       val &= ~soc_pm.sfrbu_regs.pswbu.ctrl;
+       val |= soc_pm.sfrbu_regs.pswbu.key;
        writel(val, soc_pm.data.sfrbu + offset);
-
-       /* Wait for update. */
-       val = readl(soc_pm.data.sfrbu + offset);
-       while (val & soc_pm.sfrbu_regs.pswbu.state)
-               val = readl(soc_pm.data.sfrbu + offset);
 }
 
 static void at91_pm_suspend(suspend_state_t state)
 {
        if (soc_pm.data.mode == AT91_PM_BACKUP) {
-               at91_pm_switch_ba_to_vbat();
+               at91_pm_switch_ba_to_auto();
 
                cpu_suspend(0, at91_suspend_finish);