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 14:33:32 +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 14:09, Laxman Dewangan wrote:
> 
> On Thursday 05 May 2016 06:38 PM, Jon Hunter wrote:
>> 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.
> 
> We have 2 register for DPD and hence making the mask bit will need u64.
> 
> I think we can have like below to avoid loop.
> struct tegra_io_pads_control {
>         int dpd_supported;
>         int voltage_change_supported;
>         int dpd_config_bit;
>         int voltage_config_bit;
> };

Why can't we have ...

struct tegra_io_pads_control {
        int dpd_config_bit;
        int voltage_config_bit;
	unsigned int soc_mask;
};

Then .valid should indicate if it the IO pads group is valid for the
device ...

	.soc_mask = TEGRA_IO_PADS_T124
or
	.soc_mask = TEGRA_IO_PADS_T210
or
	.soc_mask = TEGRA_IO_PADS_T124 | TEGRA_IO_PADS_T210

You can use -1 to indicate the for the dpd and voltage bit to indicate
if they are valid. In other words, you need to check the IO pad is valid
for the soc and then the bit is valid.

>>>> +    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.
>>
> We have defines in the dt binding header.

Nothing to stop us including the dt binding header in the pmc.c. We do
this for tegra clks.

> BTW, are you fine to keep TEGRA_IO_PAD_* as defines instead of enums.
> This is what POWERGATE are there.

Up to you, I prefer an enum. The POWERGATE IDs defines match the bit in
the register so it makes sense these are explicit.

Cheers
Jon