linux-kernel - Re: [PATCH] i2c: tegra: Set ACPI node as primary fwnode

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Date:   Fri, 18 Nov 2022 14:39:35 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Akhil R <akhilrajeev@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     "christian.koenig@....com" <christian.koenig@....com>,
        "digetx@...il.com" <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "wsa@...nel.org" <wsa@...nel.org>,
        Zubair Waheed <zwaheed@...dia.com>
Subject: Re: [PATCH] i2c: tegra: Set ACPI node as primary fwnode


On 18/11/2022 14:27, Akhil R wrote:
>> On 18/11/2022 10:18, Thierry Reding wrote:
>>> On Fri, Nov 18, 2022 at 09:38:52AM +0000, Jon Hunter wrote:
>>>>
>>>> On 17/11/2022 10:04, Akhil R wrote:
>>>>> Set ACPI node as the primary fwnode of I2C adapter to allow
>>>>> enumeration of child devices from the ACPI table
>>>>>
>>>>> Signed-off-by: Zubair Waheed <zwaheed@...dia.com>
>>>>> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
>>>>> ---
>>>>>     drivers/i2c/busses/i2c-tegra.c | 1 +
>>>>>     1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>>>>> index 954022c04cc4..69c9ae161bbe 100644
>>>>> --- a/drivers/i2c/busses/i2c-tegra.c
>>>>> +++ b/drivers/i2c/busses/i2c-tegra.c
>>>>> @@ -1826,6 +1826,7 @@ static int tegra_i2c_probe(struct platform_device
>> *pdev)
>>>>>     	i2c_dev->adapter.class = I2C_CLASS_DEPRECATED;
>>>>>     	i2c_dev->adapter.algo = &tegra_i2c_algo;
>>>>>     	i2c_dev->adapter.nr = pdev->id;
>>>>> +	ACPI_COMPANION_SET(&i2c_dev->adapter.dev,
>> ACPI_COMPANION(&pdev->dev));
>>>>>     	if (i2c_dev->hw->supports_bus_clear)
>>>>>     		i2c_dev->adapter.bus_recovery_info =
>> &tegra_i2c_recovery_info;
>>>>
>>>>
>>>> Do we always want to set as the primary fwnode even when booting with
>>>> device-tree? I some other drivers do, but I also see some others ...
>>>>
>>>>    if (has_acpi_companion(dev))
>>>>           ACPI_COMPANION_SET(&i2c_dev->adapter.dev,
>>>>                              ACPI_COMPANION(&pdev->dev));
>>>>
>>>> It would be nice to know why it is OK to always do this even for device-tree
>>>> because it is not clear to me.
>>>
>>> ACPI_COMPANION() returns NULL if there is no ACPI companion, which will
>>> cause ACPI_COMPANION_SET() to set the primary fwnode to NULL. If I read
>>> the code for set_primary_fwnode() correctly, that's essentially a no-op
>>> for DT devices.
>>
>> Yes it does, but doesn't it is not clear to me if it is a good idea to
>> pass NULL to set_primary_fwnode(). It does seem to handle this but my
>> biggest gripe is the lack of explanation in the commit message why this
>> is OK.
> I saw ACPI_COMPANION_SET() as an empty function if CONFIG_ACPI is not set.

That's not the issue. By default CONFIG_ACPI is enabled for arm64 but 
for Tegra we typically boot with device-tree. So I was more concerned 
about the case where ACPI_COMPANION_SET() is not an empty function.

> Yes, I agree that I should have mentioned this in the commit message.
> Shall I send a v2 with the details added in the commit description?

No need, especially as Thierry has already applied. I am not familiar 
with this function and primary/secondary fwnodes so wanted to understand 
there is no issue for device tree.

Jon

-- 
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