On 21 January 2016 at 06:26, Chen-Yu Tsai <w...@csie.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 <w...@csie.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
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