linux-kernel - Re: [PATCH 2/3] mmc: sunxi: Filter out unsupported modes declared in the device tree

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Date:   Tue, 5 Feb 2019 10:51:28 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Chris Blake <chrisrblake93@...il.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 2/3] mmc: sunxi: Filter out unsupported modes declared in
 the device tree

On Tue, Feb 05, 2019 at 04:42:53PM +0800, Chen-Yu Tsai wrote:
> On Mon, Feb 4, 2019 at 9:41 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> >
> > On Mon, Feb 04, 2019 at 06:16:24PM +0800, Chen-Yu Tsai wrote:
> > > On Mon, Feb 4, 2019 at 5:34 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > > >
> > > > On Sun, Feb 03, 2019 at 11:56:27PM +0800, Chen-Yu Tsai wrote:
> > > > > The MMC device tree bindings include properties used to signal various
> > > > > signalling speed modes. Until now the sunxi driver was accepting them
> > > > > without any further filtering, while the sunxi device trees were not
> > > > > actually using them.
> > > > >
> > > > > Since some of the H5 boards can not run at higher speed modes stably,
> > > > > we are resorting to declaring the higher speed modes per-board.
> > > > >
> > > > > Regardless, having boards declare modes and blindly following them,
> > > > > even without proper support in the driver, is generally a bad thing.
> > > > >
> > > > > Filter out all unsupported modes from the capabilities mask after
> > > > > the device tree properties have been parsed.
> > > > >
> > > > > Cc: <stable@...r.kernel.org>
> > > > > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > > > >
> > > > > ---
> > > > >
> > > > > This should be backported to stable kernels in case people try to run
> > > > > new device trees (that declare newly supported modes) with old kernels.
> > > > > ---
> > > > >  drivers/mmc/host/sunxi-mmc.c | 16 ++++++++++++++++
> > > > >  1 file changed, 16 insertions(+)
> > > > >
> > > > > diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
> > > > > index 7415af8c8ff6..a01433012db0 100644
> > > > > --- a/drivers/mmc/host/sunxi-mmc.c
> > > > > +++ b/drivers/mmc/host/sunxi-mmc.c
> > > > > @@ -1415,6 +1415,22 @@ static int sunxi_mmc_probe(struct platform_device *pdev)
> > > > >       if (ret)
> > > > >               goto error_free_dma;
> > > > >
> > > > > +     /*
> > > > > +      * If we don't support delay chains in the SoC, we can't use any
> > > > > +      * of the DDR speed modes. Mask them out in case the device
> > > > > +      * tree specifies the properties for them, which gets added to
> > > > > +      * the caps by mmc_of_parse() above.
> > > > > +      */
> > > > > +     if (!(host->cfg->clk_delays || host->use_new_timings))
> > > > > +             mmc->caps &= ~(MMC_CAP_3_3V_DDR | MMC_CAP_1_8V_DDR |
> > > > > +                            MMC_CAP_1_2V_DDR);
> > > > > +
> > > > > +     /* TODO: UHS modes untested due to lack of supporting boards */
> > > > > +     mmc->caps &= ~MMC_CAP_UHS;
> > > >
> > > > I've tested up to SDR104 and it works on the A64 at least
> > >
> > > That's good to know. What board was this on? I had given up hope waiting
> > > for a vendor to produce a board that could do proper voltage switching for
> > > SD cards.
> >
> > On a Sootech SoM, that had an HS400 eMMC and an SDR104 Marvell WiFi
> > chip. I don't have that board anymore, and the website seems down now
> > though :/
> 
> Bummer. So no commercially available board still. :/
> 
> > > > > +     /* TODO: This driver doesn't support HS200 and HS400 modes yet */
> > > > > +     mmc->caps2 &= ~(MMC_CAP2_HS200 | MMC_CAP2_HS400);
> > > >
> > > > And HS200 works too.
> > >
> > > OK. I thought there was some special magic required in the driver. Maybe
> > > that was for HS400 only? Again, what board was this on?
> >
> > Yeah, that was for HS400 only
> 
> OK. So would unblocking UHS and HS200, but not enabling them by default,
> which is essentially the original behavior, work for you?

Yep, that's perfect

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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