linux-kernel - Re: [PATCH 1/2] sdhci-of-arasan: Add quirk and device tree parameter to fake CD bit

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Message-ID: <20160825152944.GP16583@xsjsorenbubuntu>
Date:   Thu, 25 Aug 2016 08:29:44 -0700
From:   Sören Brinkmann <soren.brinkmann@...inx.com>
To:     Lars-Peter Clausen <lars@...afoo.de>
CC:     Zach Brown <zach.brown@...com>, <mark.rutland@....com>,
        <devicetree@...r.kernel.org>, <ulf.hansson@...aro.org>,
        <linux-mmc@...r.kernel.org>, <adrian.hunter@...el.com>,
        <linux-kernel@...r.kernel.org>, <robh+dt@...nel.org>,
        <michal.simek@...inx.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] sdhci-of-arasan: Add quirk and device tree parameter
 to fake CD bit

On Thu, 2016-08-25 at 17:23:47 +0200, Lars-Peter Clausen wrote:
> On 08/25/2016 05:10 PM, Sören Brinkmann wrote:
> > On Wed, 2016-08-24 at 18:23:03 -0500, Zach Brown wrote:
> >> The sdhci controller on xilinx zynq devices will not function unless
> >> the cd bit is provided. http://www.xilinx.com/support/answers/61064.html
> >> In cases where it is impossible to provide the cd bit in hardware,
> >> setting the controller to test mode and then setting inserted to true
> >> will get the controller to function with out the cd bit.
> >>
> >> The device property "fake-cd" will let the arasan driver know it needs
> >> to fake the cd bit for the controller inorder for the controller to
> >> function with a SD card that does not provide the CD bit.
> > 
> > I thought the CD is, if not pinned out, tied off to some valid logic
> > level. Isn't it enough to specify cd-inverted if needed to make it work
> > in those cases?
> 
> It is always brought out to some pin, that is the problem on the Zynq. This
> means you'd have to set at least one pin aside as dummy CD or WP pin. Which
> is not always possible when you are tight on available pins.

I have to admit that I haven't looked at Vivado for quite a while. Is it
possible to select EMIO for those pins? If those are not routed anything
they should be tied to some logic level, I believe.
If they are always forced to be on a physical pin, do you let that pin
just float? Otherwise, the logic level should also be defined, give and
take a logic inversion.

	Sören