linux-kernel - Re: [EXT] Re: [PATCH v2] mmc: core: add mmc-card hardware reset enable support

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Date:   Tue, 20 Jun 2017 12:24:14 +0200
From:   Richard Leitner <richard.leitner@...data.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        "Luca Porzio (lporzio)" <lporzio@...ron.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Richard Leitner <dev@...l1n.net>
Subject: Re: [EXT] Re: [PATCH v2] mmc: core: add mmc-card hardware reset
 enable support


On 06/20/2017 11:45 AM, Linus Walleij wrote:
>> IMHO mmc-util is where the patch really stands: the enabling is OTP,
>> the programmer have to use mmc-util only once and the kernel
>> will behave accordingly.
> 
> So we should not add it to the device tree.
> 
>> Any platform vendor must check that the HW Reset pin is actually
>> Connected BEFORE enabling this feature otherwise the system may be
>> unstable. A DT Binding may be dangerous if this condition is not met
>> as well as the code execution at each MMC init is honestly redundant
>> for an OTP location of the extCSD.
> 
> I agree. So the device should be configured during production, or
> a user who know exactly what they are doing may reconfigure it
> using the mmc-utils.
> 
> Thus the kernel should just read what the device says and stay with
> that, no DT props or anything.

Ok. Thanks for that clarification to everybody involved!

Should we then add a warning/info message to the kernel if we have a
reset gpio configured in the DT, but the eMMC hasn't this OTP bit set?

Or should we just leave it as it is? (Due to the fact the reset-gpio
could be connected to an external reset chip?)

kind regards,
Richard.L