linux-kernel - Re: [RFC 2/2] mmc: sdhci: Ignore capability register when it comes to speeds and use DT binding instead when sdhci-cap-speed-modes-broken is set.

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Date:   Wed, 19 Oct 2016 09:10:39 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Zach Brown <zach.brown@...com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] mmc: sdhci: Ignore capability register when it comes to
 speeds and use DT binding instead when sdhci-cap-speed-modes-broken is set.

On 18 October 2016 at 23:05, Zach Brown <zach.brown@...com> wrote:
> When the sdhci-cap-speed-modes-broken DT property is set, the driver
> will ignore the bits of the capability registers that correspond to
> speed modes and will read the of properties of the device to determine
> which speeds are supported.

To me this seems like a great idea. Yeah, I proposed it so I guess
that's why. :-)

Anyway, it's Adrian call to decide how he want to go with this. He
might consider the other option [1] to be better.

Some more comments below.

>
> Signed-off-by: Zach Brown <zach.brown@...com>
> ---
>  drivers/mmc/host/sdhci.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 1e25b01..100649a 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -22,6 +22,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/of.h>
>
>  #include <linux/leds.h>
>
> @@ -3020,6 +3021,32 @@ void __sdhci_read_caps(struct sdhci_host *host, u16 *ver, u32 *caps, u32 *caps1)
>  }
>  EXPORT_SYMBOL_GPL(__sdhci_read_caps);
>
> +void sdhci_get_speed_caps_from_of(struct sdhci_host *host)
> +{
> +       struct mmc_host *mmc = host->mmc;
> +
> +       host->caps &= ~SDHCI_CAN_DO_HISPD;
> +
> +       if (of_property_read_bool(mmc_dev(mmc)->of_node, "cap-sd-highspeed"))
> +               host->caps |= SDHCI_CAN_DO_HISPD;
> +
> +       if (host->version < SDHCI_SPEC_300)
> +               return;
> +
> +       host->caps1 &= ~(SDHCI_SUPPORT_SDR50 | SDHCI_SUPPORT_SDR104 |
> +                        SDHCI_SUPPORT_DDR50);
> +
> +       if (of_property_read_bool(mmc_dev(mmc)->of_node, "sd-uhs-sdr50"))
> +               host->caps1 |= SDHCI_SUPPORT_SDR50;
> +
> +       if (of_property_read_bool(mmc_dev(mmc)->of_node, "sd-uhs-sdr104"))
> +               host->caps1 |= SDHCI_SUPPORT_SDR104;
> +
> +       if (of_property_read_bool(mmc_dev(mmc)->of_node, "sd-uhs-ddr50"))
> +               host->caps1 |= SDHCI_SUPPORT_DDR50;
> +

I don't think you need a separate OF parsing function. Instead the
SDHCI variant drivers may call mmc_of_parse() to parse the generic mmc
OF properties and then read the SDHCI caps registers (in some way or
the other).

As reading the SDHCI caps registers is done in __sdhci_read_caps(),
you could instead check for the OF property
"sdhci-cap-speed-modes-broken" in there,  and if it's set, clear the
related bits. I think that's all you need.

Note, the above code considers only SD speed modes, I assume we should
include eMMC speed modes to be broken as well!?

> +}
> +
>  int sdhci_setup_host(struct sdhci_host *host)
>  {
>         struct mmc_host *mmc;
> @@ -3046,6 +3073,10 @@ int sdhci_setup_host(struct sdhci_host *host)
>                 return ret;
>
>         sdhci_read_caps(host);
> +       if (of_property_read_bool(mmc_dev(mmc)->of_node,
> +                                 "sdhci-cap-speed-modes-broken"))
> +               sdhci_get_speed_caps_from_of(host);
> +
>
>         override_timeout_clk = host->timeout_clk;
>
> --
> 2.7.4
>

Kind regards
Uffe

[1]
http://www.spinics.net/lists/devicetree/msg146401.html