linux-kernel - Re: [PATCH] pata_it8213: MWDMA0 is unsupported

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Date:	Thu, 26 Nov 2009 19:27:00 +0100
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pata_it8213: MWDMA0 is unsupported

On Thursday 26 November 2009 07:12:59 pm Sergei Shtylyov wrote:
> Bartlomiej Zolnierkiewicz wrote:
> 
> >>>>>MWDMA0 timings cannot be met with the PIIX based controller
> >>>>>programming interface.
> >>>
> >>>>>This change should be safe as this is how we have been doing
> >>>>>things in IDE it8213 host driver for years.
> >>>
> >>>>>Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
> >>>>>---
> >>>>>Verified with the documentation (similar case as with pata_efar).
> 
> >>>>Uhhh, no...
> 
> >>>>Too many damn drivers.
> 
> >>>>Too much damn duplication.
> 
> >>>>Too much damn subtle differences here and there.
> 
> >>>>The hardware is probably fine for MWMDA0 when it comes to pata_{efar,it8213},
> >>>>it just not documented properly in the data sheet.
> 
> >>>    How so with pata_efar? The active/recovery bitfields are still 2-bit 
> >>>wide, no?
> 
> >>Yes but when TIMEx bit is disabled we are using XFER_PIO_SLOW timings.
> 
>     600 ns cycle vs spec'ed 480 ns? Is it really worth it?

960 ns actually

> >>All data sheets including original Intel ones are a complete crap when it
> >>comes to explicitly documenting this behavior.
> 
> > OTOH all drivers set TIMEx for MWDMA0 currently.. ?
> 
>     ... which would give a grossly overclocked timing.

Except ata_piix which blacklists MWDMA0 for _all_ PATA controllers.. :)

I'm leaving my patches as they were for now, unless somebody wants to
untangle this mess this is a safest and quickest way forward..

--
Bartlomiej Zolnierkiewicz
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