linux-kernel - Re: [PATCH] sdhci: Add quirk and device tree parameter to force SD test mode

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Date:   Tue, 23 Aug 2016 17:14:22 -0500
From:   Zach Brown <zach.brown@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>
CC:     <ulf.hansson@...aro.org>, <mark.rutland@....com>,
        <robh+dt@...nel.org>, <linux-mmc@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sdhci: Add quirk and device tree parameter to force SD
 test mode

On Tue, Aug 23, 2016 at 09:22:29AM +0300, Adrian Hunter wrote:
> On 23/08/16 01:55, Zach Brown wrote:
> > From: Jaeden Amero <jaeden.amero@...com>
> > 
> > On some devices, CD is broken so that we must force the SDHCI into test
> > mode and set CD, so that it always detects an SD card as present.
> > 
> > In order to get a device with broken CD working, we had previously
> > always set the SDHCI into test mode. Unfortunately, this had the side
> > effect of making all SD cards used with our Linux kernels undetectable
> > and non-removable.
> > 
> > By making this "SD test mode" setting optional via a quirk, we can avoid
> > this side effect for devices other than the device with broken CD.
> > Additionally, we add a device parameter to sdhci-pltfm to allow all
> > SDHCI drivers to enable this quirk.
> 
> Generally new quirks are not acceptable, but I don't see how test mode helps
> very much since you still don't get any card detection events.  If you
> really need test mode, please explain more about how it helps (as opposed to
> polling for example).
> 
> 

Polling doesnt work in our case, since the issue lies with the SD controller
itself. The SD controller in xilinx zynq devices requires the CDn signal to
work. http://www.xilinx.com/support/answers/61064.html We have a situation 
where the controller requires the signal, but we can't use any of our pins to
supply it. With test mode we can get the controller into a state where it works
despite not having the signal.