From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <b16c5acf16741d91543edf849cfaccc9@plan9.bell-labs.com>
From: jmk@plan9.bell-labs.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] ATA next
In-Reply-To: <20040122162315.D28365@cackle.proxima.alt.za>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Date: Thu, 22 Jan 2004 10:22:37 -0500
Topicbox-Message-UUID: bd894454-eacc-11e9-9e20-41e7f4b1d025

On Thu Jan 22 09:24:40 EST 2004, lucio@proxima.alt.za wrote:
> ...
> Even more seriously (in my opinion) the IDE controller (ATA based,
> as this host has no PCI at all) is not recognised as DMA capable,
> so I get the dreaded:
> 	disabling dma: not on a busmastering controller
> message.
>
> I think jmk knows how to fix this.  ...

Remove the lines which enable DMA in whichever rc script is run at
boot, e.g. you might have something like

	for(disk in /dev/sd[C-F]*)
		echo dma on >$disk/ctl

in the cpurc for that system.

The code in sdata.c/atawctl() could perhaps be a little smarter and
not allow dmactl to be set if ctlr->prdt is nil, then at least you'd get
an error when you tried to set dma on, not later when you actually
tried some data transfers. Something like

	if(strcmp(cb->f[0], "dma") == 0){
		if(cb->nf != 2 || drive->dma == 0)
			error(Ebadctl);
		if(strcmp(cb->f[1], "on") == 0){
			ilock(ctlr);
			if(ctlr->prdt)
				drive->dmactl = drive->dma;
			else
				drive->dmactl = 0;
			iunlock(ctlr);
			if(drive->dmactl == 0)
				error("not on a busmastering controller\n");
		}
		else if(strcmp(cb->f[1], "off") == 0)
			drive->dmactl = 0;
		else
			error(Ebadctl);
	}

although I've just jotted this down and not actually tried it.