[U-Boot] [PATCH RFC] NAND: Improve read performance from Large Page NAND devices

[Nick Thompson <nick.thompson@gefanuc.com>]

On 01/12/09 10:13, Nick Thompson wrote:
> On 01/12/09 00:55, Scott Wood wrote:

>> This change will break drivers that support large page and use the 
>> default read_page functions, but do not implement cmd_ctrl (they replace 
>> cmdfunc instead).  This includes fsl_elbc_nand, mxc_nand, and 
>> mpc5121_nfc.  While I'd like to move them to implementing their own 
>> read_page-type functions instead of cmdfunc, is there any way to make it 
>> a smoother transition?
> 
> Yes, as it stands they would need modifying simultaneously and I have no
> way to test such a change myself. The only required change in cmdfunc is
> not to wait after a read0 request. You maybe in a better position to decide
> if this has wider repercussions, but I will take a look at the above
> drivers as well. [This is the main reason I made this an RFC].

How about, if nand_wait_cache_load was replaceable (by a no-op in your case)
and the pre-fetch optimisation could be disabled by setting rstate to 
(INIT | NO_REQ) on every page read function call #ifdef
CONFIG_NAND_NO_PREFETCH_READS?

This leaves a problem with NAND_CMD_RNDOUT which is used by oob_first
page reads but not supported by fsl_elbc_cmdfunc. I expect you don't use
oob_first though..?

I believe this would allow you to restore the original sequences and keep you
going until you can define your own page read functions.

[BTW these changes applied quite cleanly to my Linux tree and give similar
performance gains there as well. If we can reach agreement here, I will
make patches for Linux as well. Unfortunately, my tree is 2.6.18 with
backported NAND support from 2.6.32rc1, but I can deal with that.]

Nick.