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

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Date:   Mon, 4 Feb 2019 18:16:24 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
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 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.

> > +     /* 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?

Thanks
ChenYu