README on the SDRAM Controller for the LH7a40X==============================================The standard configuration for the SDRAM controller generates a sparsememory array.  The precise layout is determined by the SDRAM chips.  Adefault kernel configuration assembles the discontiguous memoryregions into separate memory nodes via the NUMA (Non-Uniform MemoryArchitecture) facilities.  In this default configuration, the kernelis forgiving about the precise layout.  As long as it is given anaccurate picture of available memory by the bootloader the kernel willexecute correctly.The SDRC supports a mode where some of the chip select lines areswapped in order to make SDRAM look like a synchronous ROM.  Settingthis bit means that the RAM will present as a contiguous array.  Someprogrammers prefer this to the discontiguous layout.  Be aware thatmay be a penalty for this feature where some some configurations ofmemory are significantly reduced; i.e. 64MiB of RAM appears as only 32MiB.There are a couple of configuration options to override the defaultbehavior.  When the SROMLL bit is set and memory appears as acontiguous array, there is no reason to support NUMA.CONFIG_LH7A40X_CONTIGMEM disables NUMA support.  When physical memoryis discontiguous, the memory tables are organized such that there aretwo banks per nodes with a small gap between them.  This layout wastessome kernel memory for page tables representing non-existent memory.CONFIG_LH7A40X_ONE_BANK_PER_NODE optimizes the node tables such thatthere are no gaps.  These options control the low level organizationof the memory management tables in ways that may prevent the kernelfrom booting or may cause the kernel to allocated excessively largepage tables.  Be warned.  Only change these options if you know whatyou are doing.  The default behavior is a reasonable compromise thatwill suit all users.--A typical 32MiB system with the default configuration options willfind physical memory managed as follows.   node 0: 0xc0000000 4MiB           0xc1000000 4MiB   node 1: 0xc4000000 4MiB           0xc5000000 4MiB   node 2: 0xc8000000 4MiB           0xc9000000 4MiB   node 3: 0xcc000000 4MiB           0xcd000000 4MiBSetting CONFIG_LH7A40X_ONE_BANK_PER_NODE will put each bank into aseparate node.