linux-kernel - Re: [PATCH v6 07/15] platform/x86: int3472: Enable I2c daisy chain

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Date:   Fri, 26 Nov 2021 11:56:11 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Len Brown <lenb@...nel.org>,
        linux-acpi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Kate Hsuan <hpa@...hat.com>, linux-media@...r.kernel.org,
        linux-clk@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v6 07/15] platform/x86: int3472: Enable I2c daisy chain


On 26/11/2021 11:45, Hans de Goede wrote:
> Hi,
>
> On 11/26/21 12:39, Daniel Scally wrote:
>> Hello
>>
>> On 26/11/2021 11:30, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 11/26/21 00:39, Laurent Pinchart wrote:
>>>> Hi Hans,
>>>>
>>>> Thank you for the patch.
>>>>
>>>> On Thu, Nov 25, 2021 at 05:54:04PM +0100, Hans de Goede wrote:
>>>>> From: Daniel Scally <djrscally@...il.com>
>>>>>
>>>>> The TPS68470 PMIC has an I2C passthrough mode through which I2C traffic
>>>>> can be forwarded to a device connected to the PMIC as though it were
>>>>> connected directly to the system bus. Enable this mode when the chip
>>>>> is initialised.
>>>> Is there any drawback doing this unconditionally, if nothing is
>>>> connected to the bus on the other side (including no pull-ups) ?
>>> I actually never took a really close look at this patch, I just
>>> sorta inherited it from Daniel.
>>>
>>> Now that I have taken a close look, I see that it is setting the
>>> exact same bits as which get set when enabling the VSIO regulator.
>>>
>>> The idea here is that the I2C-passthrough only gets enabled when
>>> the VSIO regulator is turned on, because some sensors end up
>>> shorting the I2C pins to ground when the sensor is not powered.
>>>
>>> Since we set these bits when powering up the VSIO regulator
>>> and since we do that before trying to talk to the sensor
>>> I don't think that we need this (hack) anymore.
>>>
>>> I will give things a try without this change and if things
>>> still work I will drop this patch from the set.
>>>
>>> Daniel, what do you think?
>>
>> Humm, we're only using the VSIO regulator with the VCM though right?
> Nope, there is a mapping from VSIO to dovdd for the ov8865 in the
> board_data; and I'm pretty sure I copied that from your earlier
> attempts at getting regulator lookups registered :)

Oh yeah derp; I was looking at the supply names rather than the
regulator names, my bad!
> And even if the VSIO regulator was only used by the VCM, then it would
> get turned off after probing the VCM, clearing the 2 bits which this
> commit sets. Which would break things if we did not re-enable it when
> the ov8865 needs it.
>
>> Which might not be on when the ov8865 tries to probe. I haven't tried
>> without this patch to be honest; I set it because that was what Windows
>> does when powering on the PMIC.
> See above, I'm pretty sure we can do without this patch which means
> that the INT3472 code will no longer be poking at the PMIC directly
> itself, which is good :)


Yeah, in that case I think you're right and this can be dropped.

> Anyways I'll give this a try sometime next week and then drop the
> patch.


Sounds good

>
> Regards,
>
> Hans
>
>
>
>
>>>>> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
>>>>> Signed-off-by: Daniel Scally <djrscally@...il.com>
>>>>> ---
>>>>>  .../x86/intel/int3472/intel_skl_int3472_tps68470.c         | 7 +++++++
>>>>>  1 file changed, 7 insertions(+)
>>>>>
>>>>> diff --git a/drivers/platform/x86/intel/int3472/intel_skl_int3472_tps68470.c b/drivers/platform/x86/intel/int3472/intel_skl_int3472_tps68470.c
>>>>> index c05b4cf502fe..42e688f4cad4 100644
>>>>> --- a/drivers/platform/x86/intel/int3472/intel_skl_int3472_tps68470.c
>>>>> +++ b/drivers/platform/x86/intel/int3472/intel_skl_int3472_tps68470.c
>>>>> @@ -45,6 +45,13 @@ static int tps68470_chip_init(struct device *dev, struct regmap *regmap)
>>>>>  		return ret;
>>>>>  	}
>>>>>  
>>>>> +	/* Enable I2C daisy chain */
>>>>> +	ret = regmap_write(regmap, TPS68470_REG_S_I2C_CTL, 0x03);
>>>>> +	if (ret) {
>>>>> +		dev_err(dev, "Failed to enable i2c daisy chain\n");
>>>>> +		return ret;
>>>>> +	}
>>>>> +
>>>>>  	dev_info(dev, "TPS68470 REVID: 0x%02x\n", version);
>>>>>  
>>>>>  	return 0;