Re: ide-cd problem

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

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@chandlerfamily.org.uk