linux-kernel - Re: [PATCH][pata-2.6 tree] pdc202xx_old: rewrite mode programming code

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Message-ID: <45EC8713.5060304@ru.mvista.com>
Date:	Tue, 06 Mar 2007 00:09:39 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	bzolnier@...il.com
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][pata-2.6 tree] pdc202xx_old: rewrite mode programming
 code

Hello, I wrote:

>> official == same as in the docs and vendor driver :-)

>>>    Erm, those look a bit doubtful...

>> I believe that they are correct - please see explanations below.

>    Yeah, sorry about that. Only SWDMA timings are suspicious.

    Hm, too early to say sorry. I was hasty/distacted and forgot what I was 
going to write... :-)

>>>> Index: b/drivers/ide/pci/pdc202xx_old.c
>>>> ===================================================================
>>>> --- a/drivers/ide/pci/pdc202xx_old.c
>>>> +++ b/drivers/ide/pci/pdc202xx_old.c
>>>
>>> [...]

>>>> @@ -161,7 +95,7 @@ static int pdc202xx_tune_chipset (ide_dr
>>>>         case XFER_UDMA_0:
>>>>         case XFER_MW_DMA_2:    TB = 0x60; TC = 0x03; break;
>>>>         case XFER_MW_DMA_1:    TB = 0x60; TC = 0x04; break;
>>>> -        case XFER_MW_DMA_0:
>>>> +        case XFER_MW_DMA_0:    TB = 0xE0; TC = 0x0F; break;

>>>    This seems even slower than SWDMA0!
>>>    Let's assume that means 7 active cycles and 15 recovery cycles 
>>> (MWDMA1/2 settings seem to confirm this hypothesis) -- this would 
>>> give us 720 ns vs the specified 480. Could you shed some light on 
>>> what these fields mean? :-/

>> The calculations are done in a different way so we get the correct 
>> timings:

>>  7 cycles (== 210 ns) are used for active time

    Ugh, forgot to say: this is overclocked, 215 ns is the minimum active time 
for this mode.

>> 16 cycles (== 480 ns) are used for cycle time

>    Ah, indeed, I've erred in MWDMA1/2 calculations. This makes sense then.

MBR, Sergei
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