linux-kernel - Re: [PATCH] pata_cmd640: CMD640 PCI support

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Date:	Sat, 3 Mar 2007 20:33:39 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Jeff Garzik <jeff@...zik.org>, akpm@...l.org,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pata_cmd640: CMD640 PCI support

> >> +    if (t.active > 16)
> >> +        t.active = 16;
> 
>     Erm, clamping active time is not a right thing to do. Right thing to do 
> was to bail out. I didn't do it in the legacy driver rewrite though...

As far as I can work out its a "can't happen"

> >> +        pci_read_config_byte(pdev, ARTIM23, &reg);
> 
>     It's not even expensive, it may be just unsafe.

You have to serialize the channels and idle both so its very expensive -
or is that what you meant by unsafe.

> >> +    /* CMD640 detected, commiserations */
> >> +    pci_write_config_byte(pdev, 0x5C, 0x00);
> 
> > magic number
> 
>    Indeed, completely undocumented. And I don't even see it in the legacy 
> driver...

Should be 0x5B which is still undocumented. Will fix that.

>     It's used to be a well known fact (soon after Intel put that chip on their 
> motherboards :-) that PCI0640 may return bad data on command block reads if 
> another channel has data port I/O going on. That's why the interrupts needed 
> to be disabled during PIO in the legacy driver (and the channels serialized).

I was under the impression this was only the situation with the
FIFO/readahead logic enabled, as with the RZ1000 ? Can you clarify that
at all ?

Alan
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