linux-kernel - Re: [PATCH V5 3/3] soc/tegra: pmc: Add support for IO pads power state and voltage

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Date:	Fri, 20 May 2016 09:58:10 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Laxman Dewangan <ldewangan@...dia.com>, <thierry.reding@...il.com>,
	<airlied@...ux.ie>, <swarren@...dotorg.org>
CC:	<gnurou@...il.com>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH V5 3/3] soc/tegra: pmc: Add support for IO pads power
 state and voltage


On 19/05/16 17:13, Laxman Dewangan wrote:
> On Thursday 19 May 2016 09:24 PM, Jon Hunter wrote:
>> On 12/05/16 13:21, Laxman Dewangan wrote:
>>> The IO pins of Tegra SoCs are grouped for common control of IO
>>> interface like setting voltage signal levels and power state of
>>> the interface. The group is generally referred as IO pads. The
>>> power state and voltage control of IO pins can be done at IO pads
>>> level.
>>>
>>> Tegra generation SoC supports the power down of IO pads when it
>>> is not used even in the active state of system. This saves power
>>> from that IO interface. Also it supports multiple voltage level
>>> in IO pins for interfacing on some of pads. The IO pad voltage is
>>> automatically detected till T124, hence SW need not to configure
>>> this. But from T210, the automatically detection logic has been
>>> removed, hence SW need to explicitly set the IO pad voltage into
>>> IO pad configuration registers.
>>>
>>> Add support to set the power states and voltage level of the IO pads
>>> from client driver. The implementation for the APIs are in generic
>>> which is applicable for all generation os Tegra SoC.
>>>
>>> IO pads ID and information of bit field for power state and voltage
>>> level controls are added for Tegra124, Tegra132 and Tegra210. The SOR
>>> driver is modified to use the new APIs.
>>>
>>> Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
>>>
>>> ---
>>> Changes from V1:
>>> This is reworked on earlier path to have separation between IO rails and
>>> io pads and add power state and voltage control APIs in single call.
>>>
>>> Changes from V2:
>>> - Remove the tegra_io_rail_power_off/on() apis and change client
>>> (sor) driver
>>> to use the new APIs for IO pad power.
>>> - Remove the TEGRA_IO_RAIL_ macros.
>>>
>>> Changes from V3:
>>> - Make all pad_id/io_pad_id to id.
>>> - tegra_io_pad_ -> tegra_io_pads
>>> - dpd_bit -> bit, pwr_mask/bit to mask/bit.
>>> - Rename function to tegra_io_pads_{set,get}_voltage_config
>>> - Make the io pad tables common for all SoC.
>>> - Make io_pads enums.
>>> - Add enums for voltage.
>>>
>>> Changes from V4:
>>> - IO_PAD->IO_PADS
>>> - TEGRA_IO_PADS_POWER_SOURCE_ -> TEGRA_IO_PADS_VCONF_
>>> ---
>>>   drivers/gpu/drm/tegra/sor.c |   8 +-
>>>   drivers/soc/tegra/pmc.c     | 221
>>> ++++++++++++++++++++++++++++++++++++++------
>>>   include/soc/tegra/pmc.h     | 132 ++++++++++++++++++--------
>>>   3 files changed, 294 insertions(+), 67 deletions(-)
>> [snip]
>>
>>> +static int tegra_io_pads_to_voltage_bit(const struct tegra_pmc_soc
>>> *soc,
>>> +                    enum tegra_io_pads id)
>>> +{
>>> +    /* T210 only supports io-pad voltage config bit */
>>> +    if (soc->io_pads_soc_mask != TEGRA_IO_PADS_T210)
>>>           return -EINVAL;
>> If this is only supported for Tegra210, should these voltage functions
>> be dependent on CONFIG_ARCH_TEGRA_210_SOC? If so, then I am also
>> wondering if we should bother having the massive look-up table and just
>> have a smaller table to translate the ID to bit for voltage as you had
>> in your initial patch? Seems there are few io-pads that support the
>> voltage configuration.
>>
> 
> Voltage config supported from T210 onwards. Earlier it was auto detected
> and so SW need not to write it.
> 
> I think let's have this as of now and we will make the different table
> for voltage config in future when we add another chip support.

Sorry, I don't follow, won't that be a massive churn to change the table
again later?

> We will not use the SOC config for this, we will use only compatible
> property and its data for getting the support.

Right, but this means that all these voltage functions are present in
the kernel image for 32-bit Tegra devices that will never use them.
Hence, I was suggesting that they should only be compiled for T210 onwards.

Cheers
Jon

-- 
nvpublic