ARM: OMAP5: Fix warm reset with USB cable connected

Warm reset on OMAP5 freezes when USB cable is connected.
Fix requires PRM_RSTTIME.RSTTIME1 to be programmed
with the time for which reset should be held low for the
voltages and the oscillator to reach stable state.

There are 3 parameters to be considered for calculating
the time, which are mostly board and PMIC dependent.
-1- Time taken by the Oscillator to shut + restart
-2- PMIC OTP times
-3- Voltage rail ramp times, which inturn depends on the
PMIC slew rate and value of the voltage ramp needed.

In order to keep the code in u-boot simple, have a way
for boards to specify a pre computed time directly using
the 'CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC'
option. If boards fail to specify the time, use a default
as specified by 'CONFIG_DEFAULT_OMAP_RESET_TIME_MAX_USEC' instead.
Using the default value translates into some ~22ms and should work in
all cases.
However in order to avoid this large delay hiding other bugs,
its recommended that all boards look at their respective data
sheets and specify a pre computed and optimal value using
'CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC'

In order to help future board additions to compute this
config option value, add a README at doc/README.omap-reset-time
which explains how to compute the value. Also update the toplevel
README with the additional option and pointers to
doc/README.omap-reset-time.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[rnayak@ti.com: Updated changelog and added the README]
Signed-off-by: Rajendra Nayak <rnayak@ti.com>

2 files changed, 20 insertions, 0 deletions

diff --git a/arch/arm/include/asm/arch-omap5/clocks.h b/arch/arm/include/asm/arch-omap5/clocks.h
index cfde374333..68afa76696 100644
--- a/arch/arm/include/asm/arch-omap5/clocks.h
+++ b/arch/arm/include/asm/arch-omap5/clocks.h
@@ -190,6 +190,10 @@
 #define OPTFCLKEN_SRCOMP_FCLK_SHIFT		8
 #define OPTFCLKEN_SRCOMP_FCLK_MASK		(1 << 8)
 
+/* PRM_RSTTIME */
+#define RSTTIME1_SHIFT				0
+#define RSTTIME1_MASK				(0x3ff << 0)
+
 /* Clock frequencies */
 #define OMAP_SYS_CLK_FREQ_38_4_MHZ	38400000
 #define OMAP_SYS_CLK_IND_38_4_MHZ	6
@@ -251,4 +255,10 @@
 #define DPLL_NO_LOCK	0
 #define DPLL_LOCK	1
 
+/*
+ * MAX value for PRM_RSTTIME[9:0]RSTTIME1 stored is 0x3ff.
+ * 0x3ff is in the no of FUNC_32K_CLK cycles. Converting cycles
+ * into microsec and passing the value.
+ */
+#define CONFIG_DEFAULT_OMAP_RESET_TIME_MAX_USEC	31219
 #endif /* _CLOCKS_OMAP5_H_ */
diff --git a/arch/arm/include/asm/arch-omap5/sys_proto.h b/arch/arm/include/asm/arch-omap5/sys_proto.h
index e66ab44341..393c8bfdb7 100644
--- a/arch/arm/include/asm/arch-omap5/sys_proto.h
+++ b/arch/arm/include/asm/arch-omap5/sys_proto.h
@@ -64,6 +64,7 @@ u32 warm_reset(void);
 void force_emif_self_refresh(void);
 void get_ioregs(const struct ctrl_ioregs **regs);
 void srcomp_enable(void);
+void setup_warmreset_time(void);
 
 /*
  * This is used to verify if the configuration header
@@ -122,4 +123,13 @@ static inline u32 omap_hw_init_context(void)
 #endif
 }
 
+static inline u32 div_round_up(u32 num, u32 den)
+{
+	return (num + den - 1)/den;
+}
+
+static inline u32 usec_to_32k(u32 usec)
+{
+	return div_round_up(32768 * usec, 1000000);
+}
 #endif