Building AM335x Linux SDK without Wayland

Brad Griffis said:

I was able to get the underflows to stop by executing this command from the console:

devmem2 0x4C000054 w 0x00FFFF30

A cleaner way of doing this same thing is to patch *u-boot* (not Linux) with the following:

From 54fe62a49719fd719e89286416da7ec88bab3e45 Mon Sep 17 00:00:00 2001
From: Brad Griffis
Date: Tue, 13 Dec 2016 11:40:27 -0600
Subject: [PATCH] [AM335x] Avoid EMIF command starvation

Section 7.3.3.5.2 "Command Starvation" of the AM335x TRM
discusses capabilities related to avoiding command starvation.
There are a couple different options, CoS or a simple counter.
This patch is enabling the simple counter mechanism.

Any systems having serious latency issues related to DDR might
consider either further reducing this timeout value or using the
more sophisticated CoS methods instead. Note that reducing this
value by too much will inhibit the EMIF's ability to optimally
order commands. The goal is to keep this value as large as
possible while still meeting all real-time deadlines.
---
arch/arm/cpu/armv7/am33xx/ddr.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/arm/cpu/armv7/am33xx/ddr.c b/arch/arm/cpu/armv7/am33xx/ddr.c
index 6acf30c..00c72c1 100644
--- a/arch/arm/cpu/armv7/am33xx/ddr.c
+++ b/arch/arm/cpu/armv7/am33xx/ddr.c
@@ -187,6 +187,10 @@ void config_sdram(const struct emif_regs *regs, int nr)
*/
void set_sdram_timings(const struct emif_regs *regs, int nr)
{
+#ifdef CONFIG_AM33XX
+ /* Enable timeout feature to avoid command starvation */
+ writel(0x00FFFF30, &emif_reg[nr]->emif_l3_config);
+#endif
writel(regs->sdram_tim1, &emif_reg[nr]->emif_sdram_tim_1);
writel(regs->sdram_tim1, &emif_reg[nr]->emif_sdram_tim_1_shdw);
writel(regs->sdram_tim2, &emif_reg[nr]->emif_sdram_tim_2);
--
2.7.4