On Wed, Oct 22, 2008 at 3:23 PM, Juha Kuikka <juha.kuikka@xxxxxxxxx> wrote:
> On Wed, Oct 22, 2008 at 3:02 PM, David Brownell <david-b@xxxxxxxxxxx> wrote:
>> On Wednesday 22 October 2008, Juha Kuikka wrote:
>>> >> - __raw_readsl(nand->IO_ADDR_R, buf, len / 2);
>>> >> + __raw_readsl(nand->IO_ADDR_R, buf, len / 4);
>>> >> }
>>> >
>>> > Shouldn't that have been __raw_readsw() though?
>>>
>>> Hmh, good point.
>>
>> Yeah, but the bug was from a patch from me ... sigh.
>>
>>
>>> From the original code it looks like that was the intention but
>>> readsl() works just as well.
>>
>> Really? Both upper and lower 16-bit units have the right data?
>
> Yes, all data comes in normally. I'm running JFFS2 on top of this.
>
>>> I tested this on OMAP2430 and it works ok.
>>>
>>> I don't see any mentions in the TRM about the width of the
>>> GPMC_NAND_DATA registers but apparently the NAND engine happily
>>> accepts 32bit accesses on bus.
>>
>> Maybe this has to do with the FIFO behavior. It would certainly
>> make sense to allow reads of any size from the FIFO. If it were
>> raw reads on the data bus, then I'd expect that both 8 and 16 bit
>> widths would work. (Assuming NAND chips weren't in parallel...)
>
> Right, for the FIFO in prefetch/writeposting block the TRM explicitly
> states that it does accept 8/16/32 bit accesses but I don't see this
> driver using the prefetch engine.
>
> No parallel chips here, just a regular 16 bit wide LP NAND.
>
>> If the FIFO is active, and specified to support arbitrary width
>> accesses (that don't match the data bus), then by all means use
>> the __raw_readsl() call to maximize bandwidth use.
>
> Sure. But interestingly enough even without explicitly using the FIFO
> it seems to accept longer bus accesses.
>
> Just to be on the safe side, maybe the patch should indeed be revised
> to use __raw_readsw(..., len/2) ?
>
How does this look?
Subject: [PATCH] OMAP2 NAND: Change __raw_readsl() to __raw_readsw()
Signed-off-by: Juha Kuikka <juha.kuikka@xxxxxxxxx>
---
drivers/mtd/nand/omap2.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index 2ede116..55ba746 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -196,7 +196,7 @@ static void omap_read_buf16(struct mtd_info *mtd,
u_char *buf, int len)
{
struct nand_chip *nand = mtd->priv;
- __raw_readsl(nand->IO_ADDR_R, buf, len / 2);
+ __raw_readsw(nand->IO_ADDR_R, buf, len / 2);
}
/*
--
1.6.0.1
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