Re: Initial signal voltage ?

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On 25 August 2015 at 14:20, Joakim Tjernlund
<joakim.tjernlund@xxxxxxxxxxxx> wrote:
> On Tue, 2015-08-25 at 14:05 +0200, Ulf Hansson wrote:
>> On 10 August 2015 at 18:50, Joakim Tjernlund
>> <joakim.tjernlund@xxxxxxxxxxxx> wrote:
>> > in mmc_power_up() we have:
>> >         /* Try to set signal voltage to 3.3V but fall back to 1.8v or 1.2v */
>> >         if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_330) == 0)
>> >                 dev_err(mmc_dev(host), "Initial signal voltage of 3.3v\n");
>> >         else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180) == 0)
>> >                 dev_err(mmc_dev(host), "Initial signal voltage of 1.8v\n");
>> >         else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_120) == 0)
>> >                 dev_err(mmc_dev(host), "Initial signal voltage of 1.2v\n");
>> >
>> > Here one jut brutally tries to set the initial power to 3.3 but nowhere in
>> > general code there is a check if the controller can handle this w.r.t
>> > HOST CAPS.
>>
>> You are right, it's brutal. :-)
>>
>> Perhaps the host driver should return -EINVAL when a voltage level
>> can't be reached. The above code should not print messages as errors,
>> at least as long some voltage level can be used.
>>
>> > Where should this check be performed, I am guessing either here or in sdhci?
>> > This is all new to me so I am just throwing this out there
>>
>> Do you want to send a patch?
>
> No, you didn't answer the question

Sorry for being a bit vague. I looked a bit more into this.

Currently drivers return error codes according to when they can't set
the requested voltage level, so that's all fine - right?

Moreover, the above code snippet is modified by you (or someone else)
locally, since in the upstream version of the code, the prints are
done a debug level. That's also okay, I think.
Perhaps changing the last print to warn level instead, since reaching
that point would mean all attempts have failed.

Kind regards
Uffe
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