linux-kernel - Re: [PATCH V2 2/2] pinctrl: tegra: Add driver to configure voltage and power of io pads

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Message-ID: <89eaabf1-c830-3ae9-5f34-a7f6d79e0816@nvidia.com>
Date:   Mon, 21 Nov 2016 11:08:43 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Laxman Dewangan <ldewangan@...dia.com>, <linus.walleij@...aro.org>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <swarren@...dotorg.org>, <thierry.reding@...il.com>
CC:     <gnurou@...il.com>, <yamada.masahiro@...ionext.com>,
        <linux-gpio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 2/2] pinctrl: tegra: Add driver to configure voltage
 and power of io pads

Hi Laxman,

On 21/11/16 09:36, Laxman Dewangan wrote:
> 
> Hi Jon,
> I will update the patch per your comment.

Thanks.

> Here is answer for some of the query.
> 
> Thanks,
> Laxman
> 
> 
> On Tuesday 15 November 2016 08:37 PM, Jon Hunter wrote:
>> On 09/11/16 13:06, Laxman Dewangan wrote:
>>> +/**
>>> + * Macro for 1.8V, keep 200mV as tolerance for deciding that
>>> + * IO pads should be set for 3.3V (high voltage) or 1.8V.
>>> + */
>>> +#define TEGRA_IO_PAD_1800000UV_UPPER_LIMIT 2000000
>> Is there a reference we could add for the source of this information?
> 
> I had a discussion with the ASIC on this and as per them
>     1.8 V nominal is (1.62V, 1.98V)
>     3.3 V nominal is (2.97V,3.63V)
> 
> I am working with them to update the TRM document but we can assume that
> this information will be there in TRM.

My feeling is that if all use-cases today are using either 1.8V or 3.3V,
then may be we should not worry about this and only support either 1.8V
or 3.3V. I would be more in favour of supporting other voltages if there
is a real need.

>>> +    const struct pinctrl_pin_desc *pins_desc;
>>> +    int num_pins_desc;
>>> +};
>>> +
>>> +struct tegra_io_pads_regulator_info {
>>> +    struct device *dev;
>>> +    const struct tegra_io_pads_cfg_info *pads_cfg;
>>> +    struct regulator *regulator;
>>> +    struct notifier_block regulator_nb;
>>> +};
>> Is this struct necessary? Seems to be a lot of duplicated information
>> from the other structs. Why not add the regulator and regulator_nb to
>> the main struct? OK, not all io_pads have a regulator but you are only
>> saving one pointer.
> Yes, some of IO pads support multi-voltage.

Yes, but I am saying why not put this information in the main struct and
not bother having yet another struct where half of the information is
duplicated.

>>
>> +        if ((vdata->old_uV > TEGRA_IO_PAD_1800000UV_UPPER_LIMIT) &&
>> +            (vdata->min_uV <= TEGRA_IO_PAD_1800000UV_UPPER_LIMIT))
>> +            break;
>> The data-sheet for Tegra210 only lists 1.8V or 3.3V as supported
>> options. Do we need to support a range? Or does the h/w support a range
>> of voltages? I am just wondering why we cannot check explicitly for 1.8V
>> or 3.3V and treat anything else as an error.
> 
> Two voltage level, not range.

Ok, then I think it would be much simpler if we just support the
voltages we are using today.

Cheers
Jon

-- 
nvpublic