On Fri, Jan 29, 2016 at 6:42 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> On 21 January 2016 at 06:26, Chen-Yu Tsai <wens@xxxxxxxx> 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@xxxxxxxx>
>> ---
>> 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.
OK. If we need to block these, then we need to block all the other
unsupported caps, which seems excessive and unnecessary. I'll drop
this patch.
Thanks
ChenYu
>
>> +
>> 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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