Re: ide-cd problem

["Alan Chandler" <alan@chandlerfamily.org.uk>]

Jens Axboe writes: 

> On Mon, Nov 22 2004, Alan Chandler wrote:
>> On Sunday 21 November 2004 16:13, Alan Chandler wrote:
>> ...
>> >
>> > This seems to be some combination of frequently occuring timing problem,
>> > and the difference treatment in cdrom_newpc_intr to cdrom_pc_intr 
>> 
>> I put a ndelay(400) at the head of cdrom_newpc_intr and the problem of
>> DRQ being set when there was no data to transfer disappeared.  It
>> appears that my hardware is too slow. 
>> 
>> I have been reading the ATA/ATAPI - 6 spec, and it implies that the
>> state of DRQ line need one pio cycle before being correct and that you
>> should read the alternative status register to achieve this.  I tried
>> a simple 
>> 
>> HWIF(drive)->INB( IDE_ALTSTATUS_REG); 
>> 
>> But that made no difference.
> 
> ALTSTATUS read should be fine as well, but the implicit delay is
> probably better. 
> 

I don't know why, but the ALTSTATUS read did NOT work when I tried it 
yesterday (am currently at work using web mail to access my mail - can't do 
more until this evening).  Its possible I put it in the wrong place (ie 
after the cdrom_decode_status call, but I don't think so. 

The ndelay(400) did work. 

> Is this enough to fix it? For ->drq_interrupt we already should have
> an adequate delay, Alan fixed this one recently. 
> 

Yes, I had included this patch quite early in my process of tracking the 
problem down (when I corrected it like you have (add the drive parameter to 
the OUTBSYNC macro like you have, you also need to declare an unsigned long 
flags at the head of the routine that was also not in that patch).  Indeed 
it was this that was the inspiration for the 400 nanosecs in my change.  I 
have no idea what the right number should be 


Alan Chandler
alan@chandlerfamily.org.uk