Re: [PATCH v2 3/3] mmc: core: add support for disabling HS400 mode via DT

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Lucas Stach <l.stach@pengutronix.de>
Cc: Chris Ruehl <chris.ruehl@gtsys.com.hk>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Haibo Chen <haibo.chen@nxp.com>, Rob Herring <robh+dt@kernel.org>,
	NXP Linux Team <linux-imx@nxp.com>,
	Sascha Hauer <kernel@pengutronix.de>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	DTML <devicetree@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 3/3] mmc: core: add support for disabling HS400 mode via DT
Date: Tue, 11 May 2021 14:19:36 +0200	[thread overview]
Message-ID: <CAPDyKFpii+q+oLqtt7he+qjqyzeUY39Oy0Wqq4cn5rXfEB6KiA@mail.gmail.com> (raw)
In-Reply-To: <0aa51fabade743fbaac70a149a771f37e7d05165.camel@pengutronix.de>

On Tue, 11 May 2021 at 13:54, Lucas Stach <l.stach@pengutronix.de> wrote:
>
> Hi Ulf,
>
> Am Dienstag, dem 11.05.2021 um 13:14 +0200 schrieb Ulf Hansson:
> > + Chris Ruehl
> >
> > On Mon, 10 May 2021 at 21:04, Lucas Stach <l.stach@pengutronix.de> wrote:
> > >
> > > From: Lucas Stach <dev@lynxeye.de>
> > >
> > > On some boards the data strobe line isn't wired up, rendering HS400
> > > support broken, even if both the controller and the eMMC claim to
> > > support it. Allow to disable HS400 mode via DT.
> >
> > Before I review the series, I just wanted to highlight that quite
> > recently we got a related series posted from Chris [1]. I made some
> > comments, but he hasn't replied yet.
> >
> > In any case, if I understood it correctly, it looks like some
> > controllers may support HS400 ES, but not HS200. Could that be the
> > case here as well? Or is this a different problem?
> >
> >
> That's not the issue I'm trying to solve here. HS400 modes, whether ES
> nor not, require the data strobe line to work. ES mode just defines how
> this line is used. I know for a fact that the board I'm dealing with
> here, just hasn't wired up this line between the SoC and the eMMC. Thus
> HS400 modes fail to work, even though both controller and eMMC support
> this mode.
>
> When HS400 is disabled, like in this series, communication falls back
> to HS200 mode and works fine this way.

Alright, thanks for clarifying. I will look into the series soon.

Kind regards
Uffe

>
> Regards,
> Lucas
>
> > Kind regards
> > Uffe
> >
> > [1]
> > https://patchwork.kernel.org/project/linux-mmc/patch/20201208061839.21163-7-chris.ruehl@gtsys.com.hk/
> >
> > >
> > > Signed-off-by: Lucas Stach <dev@lynxeye.de>
> > > ---
> > > v2:
> > > - move to core
> > > - actually disable all HS400 modes
> > > ---
> > >  drivers/mmc/core/host.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> > > index 9b89a91b6b47..0e066c5f5243 100644
> > > --- a/drivers/mmc/core/host.c
> > > +++ b/drivers/mmc/core/host.c
> > > @@ -351,6 +351,9 @@ int mmc_of_parse(struct mmc_host *host)
> > >                 host->caps2 |= MMC_CAP2_NO_SD;
> > >         if (device_property_read_bool(dev, "no-mmc"))
> > >                 host->caps2 |= MMC_CAP2_NO_MMC;
> > > +       if (device_property_read_bool(dev, "no-mmc-hs400"))
> > > +               host->caps2 &= ~(MMC_CAP2_HS400_1_8V | MMC_CAP2_HS400_1_2V |
> > > +                                MMC_CAP2_HS400_ES);
> > >
> > >         /* Must be after "non-removable" check */
> > >         if (device_property_read_u32(dev, "fixed-emmc-driver-type", &drv_type) == 0) {
> > > --
> > > 2.31.1
> > >
>
>