Re: [PATCH] IDE PIO write Fix #2

[torvalds@transmeta.com (Linus Torvalds)]

In article <3CE0D6DE.8090407@evision-ventures.com>,
Martin Dalecki  <dalecki@evision-ventures.com> wrote:
>> 
>> --- linux-2.5.15/drivers/ide/ide-taskfile.c.orig	Fri May 10 11:49:35 2002
>> +++ linux-2.5.15/drivers/ide/ide-taskfile.c	Tue May 14 10:40:43 2002
>> @@ -606,7 +606,7 @@
>>  		if (!ide_end_request(drive, rq, 1))
>>  			return ide_stopped;
>>  
>> -	if ((rq->current_nr_sectors==1) ^ (stat & DRQ_STAT)) {
>> +	if ((rq->nr_sectors == 1) ^ ((stat & DRQ_STAT) != 0)) {

Well, that's definitely an improvement - the original code makes no
sense at all, since it's doing a bitwise xor on two bits that are not
the same, and then uses that as a boolean value.

Your change at least makes it use the bitwise xor on properly logical
values, making the bitwise xor work as a _logical_ xor. 

Although at that point I'd just get rid of the xor, and replace it by
the "!=" operation - which is equivalent on logical ops.

>>  		pBuf = ide_map_rq(rq, &flags);
>>  		DTF("write: %p, rq->current_nr_sectors: %d\n", pBuf, (int) rq->current_nr_sectors);
>
>
>Hmm. There is something else that smells in the above, since the XOR operator
>doesn't seem to be proper. Why shouldn't we get DRQ_STAT at all on short
>request? Could you perhaps just try to replace it with an OR?

The XOR operation is a valid op, if you just use it on valid values,
which the patch does seem to make it do.

I don't know whether the logic is _correct_ after that, but at least
there is some remote chance that it might make sense.

		Linus