linux-kernel - Re: [PATCH V3 3/4] soc/tegra: pmc: Add support for IO pads power state and voltage

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Date:	Thu, 5 May 2016 14:08:22 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Laxman Dewangan <ldewangan@...dia.com>, <thierry.reding@...il.com>,
	<swarren@...dotorg.org>, <airlied@...ux.ie>
CC:	<gnurou@...il.com>, <dri-devel@...ts.freedesktop.org>,
	<linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 3/4] soc/tegra: pmc: Add support for IO pads power
 state and voltage


On 05/05/16 11:32, Laxman Dewangan wrote:
> 
> On Thursday 05 May 2016 03:43 PM, Jon Hunter wrote:
>> On 04/05/16 12:39, Laxman Dewangan wrote:
> 
>> +        return -EINVAL;
>> +
>> +    for (i = 0; i < soc->num_io_pads; ++i) {
>> +        if (soc->io_pads_control[i].pad_id == pad_id)
>> +            return soc->io_pads_control[i].dpd_bit_pos;
>> +    }
>> Do we need a loop here? Can't we just make the table a look-up table now
>> that the ID is just an index?
> 
> We do not support the table for all pads and so for those non supported
> pad index, it will be 0 (default) and 0 is the valid bit position here.

That does make it tricky.

> If you want table then we will need one more information for making that
> index as valid/invalid.
> We can pack the valid/invalid with bit position to make u32.

Another option would be, to have a single table for all devices and the
make the valid field a valid mask which has a bit for each SoC.

>> +    return !!(status & BIT(dpd_bit % 32));
>> +}
>> +EXPORT_SYMBOL(tegra_io_pads_power_is_enabled);
>> +
>> +int tegra_io_pads_configure_voltage(int io_pad_id, int io_volt_uv)
>> s/io_pad_id/id/
>>
>> I think I prefer tegra_io_pads_set/get_voltage_conf(). What is the point
>> in passing uV here if in device-tree you are using the enum for the
>> voltage level? I know that I had suggested this, but given we are not
>> going to use voltage in the DT then, not sure it has any value here.
> This is generic interface and hence. So in future if we have more
> option, we will not need change in interface.

Yes but apart from the SOR driver should only be used by the pinctrl
driver (I hope).

> Otherwise, make enums for 1.8/3.3 and pass as enum here. So in future if
> we have any other voltage then again add enums.
> I wanted to avoid this.

You already have added the enum for the pinctrl driver and you would
have to change that enum in the future anyway. So why not use it here?

>>   +#define TEGRA_IO_PADS_CONTROL(_pad, _dpd, _pwr)        \
>> +{                            \
>> +    .pad_id = (TEGRA_IO_PAD_##_pad),        \
>> Not sure this needs to be part of the structure as it is just an index.
> 
> it is there for matching.
> 
>>> +#define TEGRA_IO_PAD_USB2        41
>>> +#define TEGRA_IO_PAD_USB3        42
>>> +#define TEGRA_IO_PAD_USB_BIAS        43
>> Enum?
>>
> 
> Yaah, that will also be possible. Then then argument is
> 
> enum tegra_io_pad_id id
> 
> instead of unsigned int.
> 
> May be not much benifit here.

I think that this is exactly what enums are for, then you don't have to
explicitly define each number.

Cheers
Jon