On 06/25/2012 08:16 PM, Marek Vasut wrote:
Dear Scott Wood,
Note that in the case of "nand read.oob", depending on NAND page size and platform, there's a good chance that you're imposing an alignment restriction that is larger than the data being transferred even if the user asks to read the entire OOB.
I don't think I completely follow here.
Why should I need to have 64-byte alignment for transfering a 16-byte OOB?
What about "nand write.yaffs2" or multi-page "nand read.raw", which deal with arrays of interleaved main+spare? With a small page NAND chip, you'll need cache lines that are 16 bytes or smaller to avoid unaligned transactions -- and those will bypass your front-end check (unless the user is so "stupid" as to want to modify the data after a raw-read, and do a raw-write of a particular page).
Ok, I think I'm very stupid now, probably since I have high fever. I'll read this after I sleep. Sorry Scott, I'm sure you're rolling out a valid point, it's just that I'm incapable of understanding it right now.
Probably best to wait until you're feeling better for the rest of it, too. Hope you get well soon.
In the specific case of NAND, how many NAND drivers use DMA at all?
Many do,
How many? Specifically, how many that have alignment restrictions, that would need to be fixed?
At least all on the ARM architecture. And more will come, since ARM is on the rise.
atmel: no, doesn't use DMA davinci: no, doesn't use DMA kb9202: no, doesn't use DMA kirkwood: no, doesn't use DMA mxc: I don't think this uses DMA, but this driver scares me. :-) mxs: Even scarier. Looks like this one does use DMA. omap_gpmc: no, doesn't use DMA s3c64xx: no, doesn't use DMA spr: no, doesn't use DMA s3c2410: no, doesn't use DMA
If this is about not wanting to touch the mxs_nand driver again, I sympathize. :-)
it's not only nand, it's all over the place.
This patch is about NAND.
Check the whole patchset ... and that still only covers a small part of it all.
Right, I think it's wrong elsewhere too when it's user interface, but I'll let the relevant custodians argue those cases.
-Scott