[PATCHv2] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

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This patch adds comments on precatution to be taken if Global Warm reset is
used as the means to trigger sysem reset.

Signed-off-by: Vishwanath BS <vishwanath.bs@xxxxxx>
Cc: Paul Walmsley <paul@xxxxxxxxx>
---
 arch/arm/mach-omap2/prcm.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mach-omap2/prcm.c b/arch/arm/mach-omap2/prcm.c
index c201374..6494a88
--- a/arch/arm/mach-omap2/prcm.c
+++ b/arch/arm/mach-omap2/prcm.c
@@ -157,6 +157,34 @@ void omap_prcm_arch_reset(char mode, const char *cmd)
 	else
 		WARN_ON(1);
 
+	/*
+	 * As per Errata i520, In some cases, user will not be able to
+	 * access DDR memory after warm-reset.
+	 * This situation occurs while the warm-reset happens during a read
+	 * access to DDR memory. In that particular condition, DDR memory
+	 * does not respond to a corrupted read command due to the warm
+	 * reset occurence but SDRC is waiting for read completion.
+	 * SDRC is not sensitive to the warm reset, but the interconect is
+	 * reset on the fly, thus causing a misalignment between SDRC logic,
+	 * interconect logic and DDR memory state.
+	 * WORKAROUND:
+	 * Steps to perform before a Warm reset is trigged:
+	 * 1. enable self-refresh on idle request
+	 * 2. put SDRC in idle
+	 * 3. wait until SDRC goes to idle
+	 * 4. generate SW reset (Global SW reset)
+
+	 * Steps to be performed after warm reset occurs (in bootloader):
+	 * if HW warm reset is the source, apply below steps before any
+	 * accesses to SDRAM:
+	 * 1. Reset SMS and SDRC and wait till reset is complete
+	 * 2. Re-initialize SMS, SDRC and memory
+
+	 * NOTE: Above work around is required only if arch reset is implemented
+	 * using Global SW reset(GLOBAL_SW_RST). DPLL3 reset does not need
+	 * the WA since it resets SDRC as well as part of cold reset.
+	 */
+
 	if (cpu_is_omap24xx() || cpu_is_omap34xx())
 		prm_set_mod_reg_bits(OMAP_RST_DPLL3_MASK, prcm_offs,
 						 OMAP2_RM_RSTCTRL);
-- 
1.7.0.4

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