linux-kernel - Re: [PATCH RFC 03/15] mmc: sunxi: Block signal voltage switching (CMD11)

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Message-ID: <CAPDyKFrG8cXChSRuAx-a++iNHUHU_GuUApDhxfPSJZb1Oo1fsg@mail.gmail.com>
Date:	Fri, 29 Jan 2016 11:42:13 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Chen-Yu Tsai <wens@...e.org>
Cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-sunxi@...glegroups.com
Subject: Re: [PATCH RFC 03/15] mmc: sunxi: Block signal voltage switching (CMD11)

On 21 January 2016 at 06:26, Chen-Yu Tsai <wens@...e.org> wrote:
> Allwinner's mmc controller supports signal voltage switching. This is
> supported in code in Allwinner's kernel. However, publicly available
> boards all tie it to a fixed 3.0/3.3V regulator, with options to tie
> it to 1.8V for eMMC on some.
>
> Since Allwinner's kernel is an ancient 3.4, it is hard to say whether
> adapting it's code to a modern mainline kernel would work. Block signal
> voltage switching until someone has proper hardware to implement and
> test this.
>
> This only affects SD UHS-1 modes, as eMMC switches the voltage directly
> without any signaling.
>
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> ---
>  drivers/mmc/host/sunxi-mmc.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
> index 790f01662b4e..0495ae7da6d6 100644
> --- a/drivers/mmc/host/sunxi-mmc.c
> +++ b/drivers/mmc/host/sunxi-mmc.c
> @@ -816,6 +816,20 @@ static void sunxi_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
>                 }
>         }
>
> +       /*
> +        * TODO Support signal voltage switching
> +        *
> +        * Compared to Allwinner's kernel, recent updates in the mmc core
> +        * mean this should be as easy as setting the flags in cmd_val and
> +        * imask, and waiting for it to finish. However no boards support
> +        * this so this cannot be tested. Block it for now.
> +        */
> +       if (cmd->opcode == SD_SWITCH_VOLTAGE) {
> +               mrq->cmd->error = -EPERM;
> +               mmc_request_done(mmc, mrq);
> +               return;
> +       }

Unless some of the MMC_CAP_UHS* mode is set, this command shouldn't be sent.

So, if you *really* want to protect from this, I think it's better to
clear these caps in the ->probe() function, after mmc_of_parse() has
been called.

> +
>         if (cmd->opcode == MMC_GO_IDLE_STATE) {
>                 cmd_val |= SDXC_SEND_INIT_SEQUENCE;
>                 imask |= SDXC_COMMAND_DONE;
> --
> 2.7.0.rc3
>

Kind regards
Uffe