linux-kernel - Re: [PATCH v2 25/40] mmc: sdhci: Add a quirk to disable card clock during tuning

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Date:   Tue, 28 Aug 2018 18:41:29 +0300
From:   Aapo Vienamo <avienamo@...dia.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Mikko Perttunen" <mperttunen@...dia.com>,
        Stefan Agner <stefan@...er.ch>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH v2 25/40] mmc: sdhci: Add a quirk to disable card clock
 during tuning

On Mon, 27 Aug 2018 14:25:44 +0300
Adrian Hunter <adrian.hunter@...el.com> wrote:

> On 10/08/18 21:08, Aapo Vienamo wrote:
> > Add a quirk to disable card clock when the tuning command is sent.
> > 
> > This has to be done to prevent the SDHCI controller from hanging on
> > Tegra210. Without the quirk enabled there appears to be around 10%
> > chance that the tuning sequence will fail and time out due to the
> > controller locking up.
> > 
> > Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> > ---
> >  drivers/mmc/host/sdhci.c | 15 +++++++++++++++
> >  drivers/mmc/host/sdhci.h |  2 ++
> >  2 files changed, 17 insertions(+)
> > 
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index 04dc443..166b16f 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -2175,6 +2175,7 @@ static void sdhci_send_tuning(struct sdhci_host *host, u32 opcode)
> >  	struct mmc_request mrq = {};
> >  	unsigned long flags;
> >  	u32 b = host->sdma_boundary;
> > +	u16 clk;
> >  
> >  	spin_lock_irqsave(&host->lock, flags);
> >  
> > @@ -2183,6 +2184,13 @@ static void sdhci_send_tuning(struct sdhci_host *host, u32 opcode)
> >  	cmd.mrq = &mrq;
> >  
> >  	mrq.cmd = &cmd;
> > +
> > +	if (host->quirks2 & SDHCI_QUIRK2_TUNE_DIS_CARD_CLK) {
> > +		clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> > +		clk &= ~SDHCI_CLOCK_CARD_EN;
> > +		sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);  
> 
> Rather than using a quirk, could you use the sdhci I/O accessors to disable
> the clock before the tuning comment is written, udelay(1), and then enable
> it again?

This was the way it was implemented in the downstream kernel. However,
doing it in the IO accessor when a tuning command is sent seems to work
too.

 -Aapo