[U-Boot-Users] [PATCH] Fixed cfi flash read uchar bug.

[Wang Haiying-r54964 <Haiying.Wang@freescale.com>]

 
>The current code works because most CPU Bus Interface Unit 
>will execute 
>buswide cycles and discard the unused byte(s).
>
>I understand that you would like to convert this code to use memcpy() 
>and pick various bytes from local ram instead of directly from flash. 
>Right? What exactly you are experiencing when you use current code. 
>Could you refresh my memory?

The problem we experienced here is that the flash(am29lv641d) could not
get the correct size during boot up(the error message like "FLASH:
....255 erase regions found, only 4 used...0kB" is printed out), could
not be read correctly by flinfo, could not erased or written etc.
It is because the num_erase_regions got a wrong value by
flash_read_uchar(info, FLASH_OFFSET_NUM_ERASE_REGIONS)in line 1204.
It happened only after the latest update of cfi_flash driver after
u-boot 1.1.6 released. This update added a flash_read_jedec_ids before
reading num_erase_resions. We suspect that reset command in
flash_read_jedec_ids()may cause the problem. After the last reset in
this function, a flash_write_cmd() follows it, then the flash_read_uchar
is executed directly after. This flash_read_uchar returns a wrong
number(124, 255 for num_erase_regions etc.). If this flash_read_uchar
here reads some other flash info other than
FLASH_OFFSET_NUM_ERASE_REGIONS by uchar, it also returns wrong value. 

>I do not like memcpy() as it is a black box. It could be 
>implemented at 
>low level using string instructions, it could do various things for 
>different cpu architectures and various sizes so it could lead to very 
>hard to find issues.
I agree.

>My proposal for you to try: Do not depend on bus interface unit doing 
>buswide reads, explicitly read buswide chunks after doing the bus-wide 
>read into a temporary variable, pick the usable bytes from that 
>temporary variable. This should eliminate the bus interface unit 
>dependency of the CPU and possible board designer interfacing gimmicks.
Thanks a lot. :)

>Let us know how it goes (can you post your patch too so I can 
>verify it).
Zhang Wei is on vacation this week, he had generated a new patch to
implement it with the similar idea last week. He will post his new patch
after he is back.

Thanks.

Haiying