linux-kernel - Re: [PATCH 1/3] dt-bindings: mmc: Add 'fixed-emmc-driver-type-hs{200,400}'

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Message-ID: <20191105062223.GB1048@kunai>
Date:   Tue, 5 Nov 2019 07:22:23 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-mmc@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Mathieu Malaterre <malat@...ian.org>,
        Pavel Machek <pavel@....cz>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH 1/3] dt-bindings: mmc: Add
 'fixed-emmc-driver-type-hs{200,400}'

Hi Eugeniu,

thanks for this work!

> A certain eMMC manufacturer provided below requirement:
>  ---snip---
>  Use "drive strength" value of 4 or 1 for HS400 or 0 for HS200.
>  ---snip---

I see.

> The existing "fixed-emmc-driver-type" property [1] is the closest one
> to implement the above, but it falls short due to being unable to define
> two values to differentiate between HS200 and HS400 (both modes may be
> supported by the same non-removable MMC device).
> 
> To allow users to set a preferred HS200/HS400 "drive strength", provide
> two more bindings inspired from [1]:
>  - fixed-emmc-driver-type-hs200
>  - fixed-emmc-driver-type-hs400

Main question before looking at the code: Can't we just extend the
existing binding with an optional second parameter?

        minItems: 1
        maxItems: 2

I tend to favour this approach...

> For more details about eMMC I/O driver strength types, see Jedec spec.
> Keep "fixed-emmc-driver-type" in place for backward compatibility.

If we decide for the path proposed here, should the old binding be
deprecated then?

Happy hacking,

   Wolfram


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