linux-kernel - Re: [PATCH] ata: pata_at91.c bugfix for high master clock

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Date:	Sun, 12 Dec 2010 16:46:01 +0300
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	plyatov@...il.com
CC:	Sergei Shtylyov <sshtylyov@...sta.com>, jgarzik@...ox.com,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	geomatsi@...il.com
Subject: Re: [PATCH] ata: pata_at91.c bugfix for high master clock

Hello.

On 11-12-2010 22:43, Igor Plyatov wrote:

>>> I do not test this driver, but I think it have the same problem, because
>>> it have the same algorithm for timings calculation.

>>      I quickly looked thru both drivers and the algorithm seemed different. :-)

> I don't think so...

    In fact, the algorithm is slightly different.

>>> If you will see "cycle" value greater then 63, then problem exists.

>>      I thought the problem was with active pulse width, not total cycle time...

> The problem was - the same "cycle" variable used to set up NRD_CYCLE
> (max value = 127) and NCS_RD_PULSE (max value = 63).
> Where NRD_CYCLE, NCS_RD_PULSE names from datasheet for AT91SAM9.
> If NCS_RD_PULSE > 63, then overflow occur and pulse is much longer then
> required.

    Ah, NCS_RD_PULSE is different from active pulse time which is in the 
variable 'nrd_pulse'.

> For the 132 MHz, driver use NCS_RD_PULSE = 80 at device detection moment
> on my board.
> Calculated cycle in at91_ide is the same as for pata_at91 driver.

    Yes, but NCS_RD_PULSE is different in these drivers, it's cycle_time in 
at91_ide.c and (cycle time - 2) in the pata_at91.c... Then there should indeed 
be an error in at91_ide.c as well.

>>> Generally, I does not see any reasons to use at91_ide, because ATA
>>> drivers subsystem going to replace IDE drivers.

>>      There may be reasons -- like larger thruput in PIO mode (you have to check
>> this though -- but generally libata seems very slow in PIO). Anyway, it
>> doesn't mean that the bugs in IDE drivers should be ignored, and the
>> replacemtn will not happen anytime soon (not all IDE drivers are ported to
>> libata yet).

> I will send next patch where this driver corrected and tested.

    Thanks. :-)

> Best regards!
> --
> Igor Plyatov

WBR, Sergei
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