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SubjectRe: ide-cd problem
Date
Jens Axboe writes: 

> On Mon, Nov 22 2004, Alan Chandler wrote:
>> Jens Axboe writes:

>> >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.
>
> You are not answering my question :-)
>
> Here's is Alans patch as I posted some mails ago. Does it work with that
> alone?? I'm curious of it is enough. It should not be necessary to incur
> extra delay in the interrupt handler, if it is invoked from a real irq.

Sorry, I misunderstood what you meant. I presume you think that the
interrupt may be triggered immediately the command packet has been sent but
before 400ns delay had occurred.

NO - with Alan's patch alone, this did not work.

The delay seesm to be needed in the path between the interrupt occuring and
the IDE_STATUS_REG being read.

I had seen an note on a web site that said that there was two delays
required in the ATA/ATAPI spec - the 400ns which Alan's patch deals with and
a shorter delay (one PIO cycle) between busy being cleared and DRQ reaching
the correct state where the technique had been to read the ALTSTATUS
register. That was why I had tried that approach but found it not to work.

(I have subsequently downloaded a copy of the full spec and haven't been
able to find this - but then its just short of 500 pages of dense text:-)).

Thinking about it now, I tried the ALTSTATUS delay before applying Alan's
patch, so maybe its the some of the two delays that maybe necessary. If you
think its appropriate I will try that again this evening.

--
Alan Chandler
alan@chandlerfamily.org.uk

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