linux-kernel - Re: [PATCH v2] mmc: sdhci: add quirk for broken write protect detection

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Date:	Thu, 6 Mar 2014 14:31:52 +0100
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>,
	Eli Billauer <eli.billauer@...il.com>
CC:	<chris@...ntf.net>, <michal.simek@...inx.com>,
	<linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: sdhci: add quirk for broken write protect detection

On 03/04/2014 10:00 PM, Sören Brinkmann wrote:
> On Tue, 2014-03-04 at 10:06PM +0200, Eli Billauer wrote:
>> Hello Sören,
>>
>> wp-inverted solves the practical problem indeed, and fools the
>> driver into thinking that the card has an inverted write protection
>> sensor, and the logic zero that it finds in the hardware register
>> means that the card isn't write protected.
>>
>> I'm insisting on this patch, because I think that the device tree
>> should describe the hardware as it is, and not fool the driver into
>> behaving the way we want it to. These tricks always bite back later
>> on.
> Well, why is broken-wp more accurate than wp-inverted? Strictly
> speaking the WP is there and working, it's just tied off to some value
> you want to have interpreted the other way.
> Anyway, seems like this is solvable with wp-inverted and whether the
> additional quirk is needed I leave to others do decide.

I've begged for this patch - or a similar one - to be included too, because on 
our boards, the "wp" value appears to be sort of random. Out of 5 prototype 
boards, 3 would only boot with wp-inverted while the other 2 wouldn't boot 
with wp-inverted set.

In our case I really don't know (and I don't care either) to which logic level 
the wp happens to think it's wired. I just want to be able to tell the driver 
that the WP line is 
free-floating-and-might-have-any-random-value-at-any-given-moment which is a 
bit long, so I'd go for disable-wp instead.

Mike.


Met vriendelijke groet / kind regards,

Mike Looijmans

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