On Tue, 17 May 2011 13:49:44 -0400 Alex Waterman awaterman@dawning.com wrote:
Scott,
On 05/17/2011 01:05 PM, Scott Wood wrote:
On Tue, 17 May 2011 10:11:14 -0400 Alex Waterman awaterman@dawning.com wrote:
I have seen issues with the nand_read_byte16() function in nand_base.c; it seems like the cpu_to_le16() should be the other way around: le16_to_cpu(). Other than that no bugs as far as I am aware.
What is the specific problem you're seeing? The use of these endian macros is a bit abusive and ugly (what's really wanted is native-endian I/O accessors -- readw() has an implicit le16_to_cpu()), and should have been done internally to the read_word() implementation rather than made part of the API, but functionally it should be correct.
When I was getting our NAND to work, it seemed like that function was always returning 0. I fixed it by writing a read_byte() function like this:
/*
- Read a byte from the NDFC.
*/ static uint8_t tiger_read_byte(struct mtd_info *mtd){
uint16_t word; struct nand_chip *chip = mtd->priv;
word = readw(chip->IO_ADDR_R);
return (uint8_t) word;
}
It looked to me like the readw() function was returning the data in the correct CPU endianness (at least for PPC) and that the cpu_to_le16() was swapping the bytes such that the cast down to a uint8_t was getting the unset high order byte from the 16 bit read.
If readw() is returning the bytes in the correct endianness, then that means the register is little-endian.
It's not clear to me what the default assumption in nand_base.c is, though. read_byte16() suggests the default is native endian, but read_buf() and read_word() suggest it's little endian. :-(
Is there any currently working host-big-endian platform with 16-bit NAND that doesn't override these functions?
BTW, as for read_word(), looking at its only user, I think nand_block_bad() should be checking a 16-bit bad block marker on 16-bit NAND, rather than the low byte. Why is there a separate mechanism for checking bad block markers than the one in nand_bbt.c (not the bbt itself, but the code used to read the markers to create the bbt)? As long as a BBT is used, I don't think read_word() will ever matter.
-Scott