[PATCH V2] arm: mach-k3: am6_init: Prioritize MSMC traffic over DDR in NAVSS Northbridge

[Nishanth Menon]

From: Roger Quadros <rogerq at ti.com>

NB0 is bridge to SRAM and NB1 is bridge to DDR.

To ensure that SRAM transfers are not stalled due to delays during DDR
refreshes, SRAM traffic should be higher priority (threadmap=2) than
DDR traffic (threadmap=0).

This fixup is critical to provide deterministic access latency to
MSMC from ICSSG, it applies to all AM65 silicon revisions and is due
to incorrect reset values (has no erratum id) and statically setting
things up should be done independent of usecases and board.

This specific style of Northbridge configuration is specific only to
AM65x devices, follow-on K3 devices have different data prioritization
schemes (ASEL and the like) and hence the fixup applies purely to
AM65x.

Without this fix, ICSSG TX lock-ups due to delays in MSMC transfers in
case of SR1 devices, on SR2 devices, lockups were not observed so far
but high retry rates of ICSSG Ethernet (icssg-eth) and, thus, lower
throughput.

Signed-off-by: Roger Quadros <rogerq at ti.com>
Acked-by: Andrew F. Davis <afd at ti.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
Acked-by: Benoit Parrot <bparrot at ti.com>
[Jan: rebased, dropped used define, extended commit log]
Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>
[Nishanth: Provide relevant context in the commit message]
Signed-off-by: Nishanth Menon<nm at ti.com>
---

Changes in V2:
* rebase (Thanks Jan)
* Updated commit message.

V1:
https://patchwork.ozlabs.org/project/uboot/patch/20200130080503.28657-1-rogerq@ti.com/

 arch/arm/mach-k3/am6_init.c                  | 15 +++++++++++++++
 arch/arm/mach-k3/include/mach/am6_hardware.h |  6 ++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/arm/mach-k3/am6_init.c b/arch/arm/mach-k3/am6_init.c
index 425b3f93c865..ffb7aaded2e7 100644
--- a/arch/arm/mach-k3/am6_init.c
+++ b/arch/arm/mach-k3/am6_init.c
@@ -151,6 +151,19 @@ int fdtdec_board_setup(const void *fdt_blob)
 	return fixup_usb_boot();
 }
 #endif
+
+static void setup_am654_navss_northbridge(void)
+{
+	/*
+	 * NB0 is bridge to SRAM and NB1 is bridge to DDR.
+	 * To ensure that SRAM transfers are not stalled due to
+	 * delays during DDR refreshes, SRAM traffic should be higher
+	 * priority (threadmap=2) than DDR traffic (threadmap=0).
+	 */
+	writel(0x2, NAVSS0_NBSS_NB0_CFG_BASE + NAVSS_NBSS_THREADMAP);
+	writel(0x0, NAVSS0_NBSS_NB1_CFG_BASE + NAVSS_NBSS_THREADMAP);
+}
+
 void board_init_f(ulong dummy)
 {
 #if defined(CONFIG_K3_LOAD_SYSFW) || defined(CONFIG_K3_AM654_DDRSS)
@@ -168,6 +181,8 @@ void board_init_f(ulong dummy)
 	/* Make all control module registers accessible */
 	ctrl_mmr_unlock();
 
+	setup_am654_navss_northbridge();
+
 #ifdef CONFIG_CPU_V7R
 	disable_linefill_optimization();
 	setup_k3_mpu_regions();
diff --git a/arch/arm/mach-k3/include/mach/am6_hardware.h b/arch/arm/mach-k3/include/mach/am6_hardware.h
index 1908a13f0ff2..f533e22e0617 100644
--- a/arch/arm/mach-k3/include/mach/am6_hardware.h
+++ b/arch/arm/mach-k3/include/mach/am6_hardware.h
@@ -52,4 +52,10 @@
 /* MCU SCRATCHPAD usage */
 #define TI_SRAM_SCRATCH_BOARD_EEPROM_START CONFIG_SYS_K3_MCU_SCRATCHPAD_BASE
 
+/* NAVSS Northbridge config */
+#define	NAVSS0_NBSS_NB0_CFG_BASE			0x03802000
+#define	NAVSS0_NBSS_NB1_CFG_BASE			0x03803000
+
+#define	NAVSS_NBSS_THREADMAP				0x10
+
 #endif /* __ASM_ARCH_AM6_HARDWARE_H */
-- 
2.32.0