linux-kernel - Re: [PATCH] New AT91 MCI Driver that supports both MCI slots used at the same time

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Date:	Wed, 03 Jun 2009 17:10:09 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Rob Emanuele <poorarm@...reis.com>
CC:	Joey Oravec <joravec@...wtech.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org,
	Haavard Skinnemoen <hskinnemoen@...el.com>
Subject: Re: [PATCH] New AT91 MCI Driver that supports both MCI slots used
 at 	the same time

Rob Emanuele :
> Greetings Joey,

>>> +       if (host->need_reset) {
>>> +               at91_mci_write(host, AT91_MCI_CR, AT91_MCI_SWRST);
>>> +               at91_mci_write(host, AT91_MCI_CR, AT91_MCI_MCIEN);
>>> +               at91_mci_write(host, AT91_MCI_MR, host->mode_reg);
>>> +               host->need_reset = false;
>>> +       }
>>>
>> In my experience some at91s need a reset after every single command,
>> otherwise bad things happen. I think the need_reset logic is too
>> conservative in this driver.
> 
> I'll try this and probably make it an option to always reset before
> each command.

This systematic reset was remove by Haavard with this comment:
"Also, don't reset the controller between each transfer. That was an
attempt to work around earlier bugs, and it never really worked very
well."

http://lkml.org/lkml/2008/10/5/152

This reset remains in at91_mci and it does improve things on this driver
but I do not know it a better written driver can prevent from doing this...

>>> +               /*
>>> +                * WRPROOF and RDPROOF prevent overruns/underruns by
>>> +                * stopping the clock when the FIFO is full/empty.
>>> +                * This state is not expected to last for long.
>>> +                */
>>> +               host->mode_reg = (AT91_MCI_CLKDIV & clkdiv) |
>>> AT91_MCI_WRPROOF
>>> +                                       | AT91_MCI_RDPROOF;
>>>
>> These registers are not in all at91 chips especially the at91sam9261.
> 
> I'll look into this but will not be able to test every case.

Only at91rm9200 & at91sam9261/9261s are unable to setup these
functionalities.

Best regards,
-- 
Nicolas Ferre

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