On Fri, 30 Sep 2016 19:25:17 +0200
Arnd Bergmann [off-list ref] wrote:

On Friday 30 September 2016, Boris Brezillon wrote:

quoted

quoted

+     /* copy into possibly unaligned OOB region with actual length */
+     memcpy(data + bytes, eccdata, len);  

Is it better than

        for (i = 0; i < len; i += 4) {
                u32 val = __raw_readl(ecc->regs + ECC_ENCPAR(i / 4));

                memcpy(data + bytes + i, &val, min(len, 4));
        }

I'm probably missing something, but what's the point of creating a
temporary buffer of 112 bytes on the stack since you'll have to copy
this data to the oob buffer at some point?  

I tried something like that first, but wasn't too happy with it for
a number of small reasons:

- __raw_readl in a driver is not usually the right API, __memcpy32_from_io
  uses it internally, but it's better for a driver not to rely on that,
  in case we need some barriers (which we may in factt need for other drivers).

I agree, even though calling something prefixed with __ (in this case,
__ioread32_copy()) sounds like a bad thing too :).

- the min(len,4) expression is incorrect, fixing that makes it more complicated
  again

Sorry, it's min(len - i, 4), which is not that complicated :P.

- I didn't like to call memcpy() multiple times, as that might get turned
  into an external function call (the compiler is free to optimize small
  memcpy calls or not).

Okay.

I agree that he 112 byte buffer isn't ideal either, it just seemed to
be the lesser annoyance.

How about we keep your approach, but put the buffer in the mtk_ecc
struct?