linux-kernel - Re: [PATCH v7 00/13] mmc: Add support to Marvell Xenon SD Host Controller

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Date:   Fri, 31 Mar 2017 10:09:58 +0800
From:   Hu Ziji <huziji@...vell.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Gregory CLEMENT <gregory.clement@...e-electrons.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        <linux-mmc@...r.kernel.org>, Jimmy Xu <zmxu@...vell.com>,
        Andrew Lunn <andrew@...n.ch>,
        Mike Turquette <mturquette@...libre.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Victor Gu <xigu@...vell.com>, Doug Jones <dougj@...vell.com>,
        <linux-clk@...r.kernel.org>, Jisheng Zhang <jszhang@...vell.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Kostya Porotchkin <kostap@...vell.com>,
        Hanna Hawa <hannah@...vell.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        <devicetree@...r.kernel.org>, Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>, Ryan Gao <ygao@...vell.com>,
        "Wei(SOCP) Liu" <liuw@...vell.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        <linux-kernel@...r.kernel.org>, Wilson Ding <dingwei@...vell.com>
Subject: Re: [PATCH v7 00/13] mmc: Add support to Marvell Xenon SD Host
 Controller

Hi Russell,

On 2017/3/31 2:56, Russell King - ARM Linux wrote:
> ----------------------------------------------------------------------
> On Thu, Mar 30, 2017 at 05:22:52PM +0200, Gregory CLEMENT wrote:
>> - Remove parse of child node mmc-card. Wait for a better solution.
> 
> So for mcbin, I have:
> 
> &ap_sdhci0 {
>         bus-width = <8>;
>         marvell,xenon-emmc;
>         marvell,xenon-phy-type = "emmc 5.1 phy";
>         /*
>          * Not stable in HS modes - phy needs "more calibration", so add
>          * the "slow-mode" and disable SDR104, SDR50 and DDR50 modes.
>          */
>         marvell,xenon-phy-slow-mode;
>         no-1-8-v;
>         non-removable;
>         status = "okay";
>         vqmmc-supply = <&v_vddo_h>;
> 
>         #address-cells = <1>;
>         #size-cells = <0>;
>         mmccard: mmccard@0 {
>                 compatible = "mmc-card";
>                 reg = <0>;
>         };
> };
> 
> Does this mean the "mmccard" bit is no longer required - or is it required
> for the eMMC to be detected but is no longer supported by the driver?
> 

	Based on the implementation in this release, "mmccard" is no longer required.

	More details:
	eMMC Vqmmc in Xenon is fixed without a regulator. Thus 1.8V Signaling Enable bit
	in SDHC doesn't work.
	As a result, Xenon driver has to skip sdhci_start_signal_voltage_switch() to avoid
	checking 1.8V signaling enable bit when setting signaling voltage.

	Previously, we use "mmccard" to inform Xenon driver that it is an eMMC card
	and therefore sdhci_start_signal_voltage_switch() is skipped.

	Currently, Xenon driver directly checks if Vqmmc regulator is provided.
	Skip sdhci_start_signal_voltage_switch() if Vqmmc is fixed.
	In my own opinion, it is more direct and clear, than checking eMMC card type. 

	Thank you.

Best regards,
Hu Ziji

> Thanks.
>