Re: ide-cd problem

[Alan Chandler]

Jens Axboe writes: 

> On Mon, Nov 22 2004, Alan Chandler wrote:
> > 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 
>
> 400ns is the correctl value. Your writing is a little unclear to me -
> did it work or not, with that change alone? 

To be clear ... 


I have modified ide-cd.c with 

1) ndelay(400) at the head of cdrom_newpc_intr() 

2) Alan Cox's patch in the place he originally identified for it to go 

3) Some printk's in cdrom_newpc_intr() after the point where it reads the 
status and IREASON and length registers and just for the purposes of 
diagnostics. 

With only those changes it now works. 



Alan Chandler
alan@xxxxxxxxxxxxxxxxxxxxx 

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