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

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Date:	Thu, 6 Mar 2014 08:42:48 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
CC:	Eli Billauer <eli.billauer@...il.com>, <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 Thu, 2014-03-06 at 02:31PM +0100, Mike Looijmans wrote:
> 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.

Could you provide the design you use and give more details? According to
the people I talked to, the signal should never float, unless you pin it
out and don't drive it.
Actually, you should open a support case for this. It is not supposed to
happen.

	Sören


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