Re: 2.6.29-rc libata sff 32bit PIO regression

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Hello.

Hugh Dickins wrote:

(though much more verbose: please simplify if you see a better way).
  How about the following?

		unsigned char *tail = buf + buflen - slop;
		unsigned char pad[4];

		if (rw == READ) {
			if (slop <= 2)
				ioread16_rep(data_addr, pad, 1);
			else
				ioread32_rep(data_addr, pad, 1);
					memcpy(tail, pad, slop);

Too many tabs on the memcpy.

Hey, this is not a patch, and I was using Thunderbird's msg editor -- which isn;t really good to tabs. :-)

		} else {
			memcpy(pad, tail, slop);
			memset(pad + slop, 0, 4 - slop);

And we could make that line even more complicated!

  We could use memzero() but memset() should boil down to it anyway.

But I think unsigned char pad[4] = {0, 0, 0, 0} would be better.

Not really, we don't need to waste time initiazlizing it on reads -- I hope you understand that it will require real code to write all those zeros?). Besides, only {0} should be enough as other entries should be implitly zeroed).

Though Alan didn't have it initialized at all: I don't know if
that was oversight or superior knowledge.  In Alan's case, one
should usually assume the latter.

  These bytes can be anything actually as a device should just ignore them.

		if (slop <= 2)
				iowrite16_rep(data_addr, pad, 1);
			else
				iowrite32_rep(data_addr, pad, 1);
		}

Well, I don't know.

  I do. :-)

I felt really pleased with using ioread16_rep
and the char array in my original patch, where slop might be 1 or 2
or 3; but once it comes down to always one single PIO op, I felt
it too lazy to be using the _rep form.

It should do the Right Thing WRT the byte reordering (which is a lack thereof ;-) while your code had to muck with it explicitly. And of course it's shorter -- because of that.

I really don't care, whatever works and best satisfies Alan.

I thought we should care about general user satisfaction, not just Alan's... :-)

-	return words << 2;
+
+	return buflen + (buflen & 1);
   return (buflen + 1) & ~1;

  Well, I guess I could just have posted my own patch... :-)

Yes, do go ahead, I'm not desperate to get my name in there!

I'm not actually very enthusiastic in getting blamed for the breakage, given the Alan's example. ;-)

Hugh

MBR, Sergei


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