mips: mt76xx: Implement new d-cache fix in last_stage_init()

With commit 06985289d452 ("watchdog: Implement generic watchdog_reset()
version") the init sequence has changed in arch_misc_init(), resulting
in a re-appearance of the d-cache issue on MT7688 boards (e.g. gardena).
When this happens, the first (or sometimes later ones as well) TFTP
command hangs and does not complete correctly. This leads to the
assumption that the d-cache is not in a clean state once the ethernet
driver is called (d-cache is used here for the buffers). The old work-
around with the cache flush somehow does not work any more now with
the new code change.

Unfortunately adding CONFIG_SYS_MALLOC_CLEAR_ON_INIT also did not fix
this issue. With v2019.07-rc3 it shows again. The time of accessing
the data seems to be very important here. It needs to be "very late"
in the boot process.

Testing has shown, that copying a 64KiB area in DDR at a very late
bootup time, directly before calling into the prompt, fixes this issue.
Flushing of the complete d-cache does not seem to necessary, as this
copy alone seems to fix this problem.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 5cb9bdf2ee7a771db534808448cf70b034b77376..e3e79455679912361d8ff9722928dddcb57b385c 100644 (file)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -84,13 +84,13 @@ config ARCH_MTMIPS
        select DM_SERIAL
        imply DM_SPI
        imply DM_SPI_FLASH
+       select LAST_STAGE_INIT
        select MIPS_TUNE_24KC
        select OF_CONTROL
        select ROM_EXCEPTION_VECTORS
        select SUPPORTS_CPU_MIPS32_R1
        select SUPPORTS_CPU_MIPS32_R2
        select SUPPORTS_LITTLE_ENDIAN
-       select SYS_MALLOC_CLEAR_ON_INIT
        select SYSRESET
 
 config ARCH_JZ47XX

diff --git a/arch/mips/mach-mtmips/cpu.c b/arch/mips/mach-mtmips/cpu.c
index b0a6397d68f0a5366246a4b960f11fb08239d416..7afc2c5940d3a88e3e283ba36249b4961d183a18 100644 (file)
--- a/arch/mips/mach-mtmips/cpu.c
+++ b/arch/mips/mach-mtmips/cpu.c
@@ -68,3 +68,29 @@ int print_cpuinfo(void)
 
        return 0;
 }
+
+int last_stage_init(void)
+{
+       void *src, *dst;
+
+       src = malloc(SZ_64K);
+       dst = malloc(SZ_64K);
+       if (!src || !dst) {
+               printf("Can't allocate buffer for cache cleanup copy!\n");
+               return 0;
+       }
+
+       /*
+        * It has been noticed, that sometimes the d-cache is not in a
+        * "clean-state" when U-Boot is running on MT7688. This was
+        * detected when using the ethernet driver (which uses d-cache)
+        * and a TFTP command does not complete. Copying an area of 64KiB
+        * in DDR at a very late bootup time in U-Boot, directly before
+        * calling into the prompt, seems to fix this issue.
+        */
+       memcpy(dst, src, SZ_64K);
+       free(src);
+       free(dst);
+
+       return 0;
+}