linux-kernel - Re: How to disable DMA for compact-flash disk?

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Message-ID: <20090814221038.19e868a0@lxorguk.ukuu.org.uk>
Date:	Fri, 14 Aug 2009 22:10:38 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Ben Greear <greearb@...delatech.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: How to disable DMA for compact-flash disk?

> This worked fine, but now I'm having some more issues.  Using libata is 1/2
> as fast as using IDE mode.  I *think* the problem might be that libsata
> may not be using 32-bit PIO mode, but I'm not certain of that.  It seems
> that ide mode uses PIO2 v/s PIO4 for libsata too.

As of 2.6.29 libata doesn't use 32bit PIO (it shouldn't make a difference
for most chipsets but it does for some). 2.6.30 does for some and you can
turn it on for others if you want to test by inheriting
ata_bmdma32_port_ops instead of ata_bmdma_port_ops

> hdb: Ridata CF, CFA DISK drive
> hdb: host max PIO5 wanted PIO255(auto-tune) selected PIO2
> hdb: host max PIO5 wanted PIO255(auto-tune) selected PIO2

Very odd it picked PIO2, but the numbers you quote for hdparm doesn't
sound like PIO2 so its hard to guess.

> ata1.01: configured for PIO4

So libata picked a faster rate (PIO4 is the fastest the controller is
properly specced for according to my docs - it probably can do PIO5 (CF
specific))

> /dev/sda1:
>   Timing cached reads:   280 MB in  2.00 seconds = 139.98 MB/sec
>   Timing buffered disk reads:   10 MB in  3.69 seconds =   2.71 MB/sec

Would be very interested to know if bmdma32_port_ops gives you the speed.
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