[U-Boot] [PATCH] arm: sunxi: do not force USB for arch-sunxi

[Yann E. MORIN]

Currently, USB is forced-enabled for the sunxi familly, and there is no
way to disable it.

However, USB takes a long time to initiliase, delaying the boot by up to
5 seconds (without any USB device attached!). This is a very long delay,
especially in cases where USB booting is not wanted at all, and where
the device is expected to boot relatively often (even in production).

Change the way the dependencies are handled, by only forcibly selecting
USB when CONFIG_DISTRO_DEFAULTS ("defaults suitable for booting general
purpose Linux distributions") is set. This option defaults to y for the
sunxi familly, so the current default behaviour is kept unchanged. Users
interested in boot time and/or size will be able to disable this to
further disable USB.

With USB disabled, the time spent in U-Boot before handing control to
the Linux kernel is about 1s now, down from ~5s (Nanopi Neo, sunxi H3).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Cc: Ian Campbell <ijc at hellion.org.uk>
Cc: Hans De Goede <hdegoede at redhat.com>

---
This is a tentative patch, acting as an RFC (unless it is good to go as
is, of course!).

This has been discussed on IRC with <ssvb> and <apritzel>, and this
solution is what emerged from the discussions as a first step.

The second step would be to defer intialisation of drivers until they
are actually needed, i.e. if main boot is not from USB, then don't
initiliase USB; if main boot fails, then initialise addtional drivers,
like USB... Or something along those lines... That's a much tougher
work for me, though...

There are other features that are currently forced like USB, but USB
is by far the worst "offender" and a low-hanging fruit. Those other
"offenders" can be handled in follow up changes.
---
 arch/arm/Kconfig | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index d7a9b11..c13f60f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -561,22 +561,22 @@ config ARCH_SUNXI
 	bool "Support sunxi (Allwinner) SoCs"
 	select CMD_GPIO
 	select CMD_MMC if MMC
-	select CMD_USB
+	select CMD_USB if DISTRO_DEFAULTS
 	select DM
 	select DM_ETH
 	select DM_GPIO
 	select DM_KEYBOARD
 	select DM_SERIAL
-	select DM_USB
+	select DM_USB if DISTRO_DEFAULTS
 	select OF_BOARD_SETUP
 	select OF_CONTROL
 	select OF_SEPARATE
 	select SPL_STACK_R if SUPPORT_SPL
 	select SPL_SYS_MALLOC_SIMPLE if SUPPORT_SPL
 	select SYS_NS16550
-	select USB
-	select USB_STORAGE
-	select USB_KEYBOARD
+	select USB if DISTRO_DEFAULTS
+	select USB_STORAGE if DISTRO_DEFAULTS
+	select USB_KEYBOARD if DISTRO_DEFAULTS
 	select USE_TINY_PRINTF
 
 config TARGET_TS4800
-- 
2.7.4