about jffs2's compression and cfi->fast_prog being turn off

about jffs2's compression and cfi->fast_prog being turn off

[Jack Lu]

Hi
	I read the paper posted on May5th 2001 by Vinip Malik, it says:

One down side to this is that if you are writing compressed data to the
system, the CPU will spend time trying to compress it further. At this time
of writing, compression cannot be turned off. There are some plans to
implement this feature however (even turn it off on a directory by directory
basis!).

Now I have set up the jffs2 file system using the latest source code
downloadded from website.

1. With this latest jffs2, can we turn  off the compression? If can , how
can we turn it?


By the way, our compression algorithm is the CCITT Group 4 compression of
bi-level image, the image written to a file with TIFF6.0 file format.

2. If we still use the jffs2 compression after we compress the image using
CCITT4 Group algorithm, could it help us to reduce  the size to store the
compressed image into the flash memory?

3. With the latest jffs2, the erase suspend is implemented for AMD CFI
chips, such as Am29Lv320MB?

4. The cfi_cmdset_0002.c file includes:

	if (cfi->fast_prog) {
		/* In cfi_amdstd_write() we frob the protection stuff
		   without paying any attention to the state machine.
		   This upsets in-progress erases. So we turn this flag
		   off for now till the code gets fixed. */
		printk(KERN_NOTICE "cfi_cmdset_0002: Disabling fast programming due to
code brokenness.\n");
		cfi->fast_prog = 0;
	}
Turnning off the cfi->fast_prog will affect the the time needed to program
the flahsh?


Thanks.

Re: about jffs2's compression and cfi->fast_prog being turn off

[David Woodhouse]

jlu@rdmcorp.com said:
>  1. With this latest jffs2, can we turn  off the compression? If can ,
> how can we turn it? 

Not implemented yet. Send patch -- it's quite simple :)

>  2. If we still use the jffs2 compression after we compress the image
> using CCITT4 Group algorithm, could it help us to reduce  the size to
> store the compressed image into the flash memory? 

It's unlikely that further compression will have any useful effect. You 
could try telling it to attempt only 'rtime' compression, but just telling 
it not to compress the file(s) in question would be best.

>  3. With the latest jffs2, the erase suspend is implemented for AMD
> CFI chips, such as Am29Lv320MB? 

JFFS2 knows nothing of such things. The current cfi_cmdset_0002 code does 
not support erase suspend. I've never had hardware I can test on, and 
nobody's submitted a patch known to be working. Again, fairly simple to 
implement this yourself.

> Turnning off the cfi->fast_prog will affect the the time needed to
> program the flahsh?

It shouldn't make a lot of difference.


--
dwmw2