linux-kernel - Re: [PATCH 6/10] mmc: sdhci-xenon: Add Marvell Xenon SDHC core functionality

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Date:   Fri, 25 Nov 2016 16:04:50 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>, Ziji Hu <huziji@...vell.com>
Cc:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Jimmy Xu <zmxu@...vell.com>,
        Jisheng Zhang <jszhang@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>, Ryan Gao <ygao@...vell.com>,
        Doug Jones <dougj@...vell.com>, Victor Gu <xigu@...vell.com>,
        "Wei(SOCP) Liu" <liuw@...vell.com>,
        Wilson Ding <dingwei@...vell.com>,
        Romain Perier <romain.perier@...e-electrons.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Hanna Hawa <hannah@...vell.com>,
        Kostya Porotchkin <kostap@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Zhen Huang <huangzh@...vell.com>
Subject: Re: [PATCH 6/10] mmc: sdhci-xenon: Add Marvell Xenon SDHC core
 functionality

On 24/11/16 15:34, Ulf Hansson wrote:
> On 24 November 2016 at 13:41, Ziji Hu <huziji@...vell.com> wrote:
>> On 2016/11/24 18:43, Ulf Hansson wrote:
>>> On 31 October 2016 at 12:09, Gregory CLEMENT
>>> <gregory.clement@...e-electrons.com> wrote:
>>>> From: Ziji Hu <huziji@...vell.com>
>>>> +static int xenon_start_signal_voltage_switch(struct mmc_host *mmc,
>>>> +                                            struct mmc_ios *ios)
>>>> +{
>>>> +       struct sdhci_host *host = mmc_priv(mmc);
>>>> +       struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>>> +       struct sdhci_xenon_priv *priv = sdhci_pltfm_priv(pltfm_host);
>>>> +
>>>> +       /*
>>>> +        * Before SD/SDIO set signal voltage, SD bus clock should be
>>>> +        * disabled. However, sdhci_set_clock will also disable the Internal
>>>> +        * clock in mmc_set_signal_voltage().
>>>
>>> If that's the case then that is wrong in the generic sdhci code.
>>> What's the reason why it can't be fixed there instead of having this
>>> workaround?
>>>
>>     In my very own opinion, SD Spec doesn't specify whether SDCLK should be
>>     enabled or not during power setting.
>>     Enabling SDCLK might be a special condition only required by our SDHC.
>>     I try to avoid breaking other vendors' SDHC functionality
>>     if their SDHCs require SDCLK disabled.
>>     Thus I prefer to keep it inside our SDHC driver.
> 
> I let Adrian comment on this.
> 
> For sure we should avoid breaking other sdhci variant, but on the
> other hand *if* the generic code is wrong we should fix it!

Yes, this looks like something that could perhaps be fixed in sdhci.  I will
look into it.