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: <d5dd97b1-f58f-2e45-5c95-17a77a46b30c@metafoo.de>
Date:   Thu, 25 Aug 2016 17:23:47 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Sören Brinkmann <soren.brinkmann@...inx.com>,
        Zach Brown <zach.brown@...com>
Cc:     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 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.