linux-kernel - Re: [PATCH] pata_it821x: sync with IDE it821x driver

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Date:	Sat, 9 Jun 2007 22:09:10 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	Jeff Garzik <jeff@...zik.org>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pata_it821x: sync with IDE it821x driver


Hello,

On Saturday 09 June 2007, Tejun Heo wrote:
> Hello,
> 
> Bartlomiej Zolnierkiewicz wrote:
> > * (partially) fix DMA in RAID mode
> > 
> >   Code intended to check DMA status was checking DMA command register.
> >   Moreover firmware seems to "forget" to set DMA capable bit for the
> >   slave device (at least in RAID mode but without ITE RAID volumes) so
> >   check device ID for DMA capable bit when deciding whether to use DMA
> >   and remove DMA status check completely.
> > 
> >   Thanks to Pavol Šimo for the bugreport and testing the initial fix.
> 
> Ah... This is the mysterious mwdma configuration in smart mode, right?

Yep.

> Thanks for fixing this.
> 
> >   This change unfortunately still doesn't fix DMA in RAID mode (which
> >   works fine with IDE it821x) but Alan is working on the missing pieces
> >   (pata_it821x vs libata EH issues).
> 
> This is the lbal/nsect SRST problem, right?

I think so, due to lack of time I'm not following libata discussions closely.

> > @@ -258,8 +259,14 @@ static void it821x_passthru_set_piomode(
> >  	static const u8 pio_want[]    = { ATA_66, ATA_66, ATA_66, ATA_66, ATA_ANY };
> >  
> >  	struct it821x_dev *itdev = ap->private_data;
> > +	struct ata_device *pair = ata_dev_pair(adev);
> >  	int unit = adev->devno;
> > -	int mode_wanted = adev->pio_mode - XFER_PIO_0;
> > +	int mode_wanted = adev->pio_mode;
> > +
> > +	if (pair && adev->pio_mode > pair->pio_mode)
> > +		mode_wanted = pair->pio_mode;
> > +
> > +	mode_wanted -= XFER_PIO_0;
> 
> I think this is better done by mode_filter callback which is guaranteed
> to be called before any actual mode configuration is performed and in
> device order (master then slave).

I was thinking about using ->mode_filter but since all other PATA host
drivers are doing PIO filtering in ->set_piomode methods and also since it
seemed that using ->mode_filter method would result in slightly more complex
code I opted for coherency / simplicity.  However if you (or somebody else)
want to make a follow-up change to this driver (and preferably other PATA
host drivers ie. pata_sil680) to use ->mode_filter I'm also fine with that.

Thanks,
Bart
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