Hi Wolfgang,
On Monday 16 May 2011 01:35 AM, Wolfgang Denk wrote:
Dear Aneesh V,
In message1305472900-4004-17-git-send-email-aneesh@ti.com you wrote:
Calculate EMIF register values based on AC timing parameters from the SDRAM datasheet and the DDR frequency rather than using the hard-coded values.
For a new board the user doen't have to go through the tedious process of calculating the register values. Instead, just provide the AC timings from the device data sheet as input and the driver will automatically calculate the register values.
Does it make sense to do this in the driver code? These parameters will never change, so why can we not rather perform the computation only once, at build time, and feed in the respective parameters to the driver?
Some of the parameters do change. For instance on one of the OMAP4 revisions the DDR runs at 200MHz, on another one at 380MHz and for the rest at 400MHz. Also, on ES1 we have 512 MB of memory where as on others we have 1GB. This driver is also doing discovery of SDRAM geometry, type, etc.
Reasons why I am concerned about such an approach are code size and boot time. Both suffer ...
I had the same concerns too. So, I have provided a CONFIG option - CONFIG_SYS_EMIF_PRECALCULATED_TIMING_REGS - by which the user can provide the register values, so no computation will be done.
So, if somebody is concerned about the performance they can just compute the values using this driver and print them out by enabling the debug traces, fill it up in the structs provided for it and enable CONFIG_SYS_EMIF_PRECALCULATED_TIMING_REGS. That should work.
Also, please note that I had measured the time taken for the entire SDRAM initialization and it was not at all significant(IIRC, it was less than 1ms).
best regards, Aneesh