cs5536: Make NAND code optional and implement timing setting

The reset value for NAND timings is the slowest possible for Flash interface.
Implement optionally setting it to a different value inside the NAND device.
Set it to appropriate values for Artec Group DBE61 and DBE62.
This results in a roughly two times quicker read time as measured by hdparm
for these boards.

Because we can not cast to southbridge_amd_cs5536_nand_config if the board dts
does not have an entry for the NAND device, this change proposes a method for
reasonably clean way to only optionally compile in support for certain devices:
If a board wants to support an optional device, its Kconfig entry can select
that configuration. If it's optional even across the same board, it can expose
a subconfig option of the board, that describes it and if chosen selects the
device config. The source code for that device is conditionally compiled only
if the Kconfig option gets enabled by the configuration for the board.
A requirement is that if the board configuration can enable a device, it is
contained in the boards dts file as well.

A perhaps better long-term alternative for this could be making dtc generate
preprocessor definitions for each device_configuration struct that it creates.
Then the source code file is always enabled, but that file can be wrapped
around a simple #ifdef check in its entirety.

Conversion to the alternative approach from the short-term Kconfig approach
proposed here should be relatively easy, as to not block inclusion of the
Kconfig approach in the short term.

Signed-off-by: Mart Raudsepp <mart.raudsepp@artecdesign.ee>
Acked-by: Marc Jones <marcj303@gmail.com>

git-svn-id: svn://coreboot.org/repository/coreboot-v3@1138 f3766cd6-281f-0410-b1cd-43a5c92072e9

1 files changed, 5 insertions, 0 deletions

diff --git a/Kconfig b/Kconfig
index 82e2c44af4f5..8adc0451e6ae 100644
--- a/Kconfig
+++ b/Kconfig
@@ -163,6 +163,11 @@ config SUPERIO_ITE_IT8712F
 config SUPERIO_VIA_VT1211
 	boolean
 
+# Other devices that may be optional for a board:
+config DEVICE_AMD_CS5536_NAND
+	select SOUTHBRIDGE_AMD_CS5536
+	boolean
+
 menu "Payload"
 
 config PAYLOAD_ELF_LOADER