Support of stupid devices

Support of stupid devices

[Ian Molton]

Hi.

Im porting linux to the toshiba e7xx and 8xx PDAs which contain a nand flash controller.

Im not certain, but it appears the controllerhas an odd quirk meaning byte-reads of the data register dont work as the linux mtd code expects.

AFAICT if I read a word (after issuing a chipid command) I get:

0xYYZZ75ec   -- this is good - Samsung, 32MB device.

if I do two byte reads I get 0xec 0xec.

a halfword access gets me 0xYYZZ.

a misaligned (by one byte) word access gives me 0xecYYZZ75, but this fails to work for byte accesses. halfword misaligned accesses are just weird.

so basically, the only way to read the chipid is to do:

a word access to the data reg and then shift the data out

or

a word access (and mask off the high 3 bytes followed by a misaligned word access and mask off the upper 3 bytes.

clearly the former solution is the better one, but this doesnt fit in the nand driver model very well (read_byte() et.al.)

the chip is a TC6393XB (system on chip) and the flash is a samsung K9F5608UOC YCBO

Re: Support of stupid devices

[Thomas Gleixner]

On Mon, 2004-08-16 at 02:39, Ian Molton wrote:
> Hi.
> 
> Im porting linux to the toshiba e7xx and 8xx PDAs
> which contain a nand flash controller.
> Im not certain, but it appears the controllerhas an
> odd quirk meaning byte-reads of the data register
> dont work as the linux mtd code expects.
> 
> AFAICT if I read a word (after issuing a chipid command) I get:
> 
> 0xYYZZ75ec   -- this is good - Samsung, 32MB device.
> 
> if I do two byte reads I get 0xec 0xec.
> 
> a halfword access gets me 0xYYZZ.
> a misaligned (by one byte) word access gives me 0xecYYZZ75, 

Sounds really stupid :)

> but this fails to work for byte accesses. halfword misaligned
> accesses are just weird.
> so basically, the only way to read the chipid is to do:
> a word access to the data reg and then shift the data out
> or
> a word access (and mask off the high 3 bytes followed by a
> misaligned word access and mask off the upper 3 bytes.
> clearly the former solution is the better one, but this 
> doesnt fit in the nand driver model very well 
> (read_byte() et.al.)

You can provide your own read_byte() et. al. functions which do all the
magic. Look into the other Toshiba nand driver implementations. They do
the same. I don't have the header files which implement the real access
but Alice should be a source of help.

> the chip is a TC6393XB (system on chip) and the flash 
> is a samsung K9F5608UOC YCBO

tglx


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