linux-kernel - Re: [PATCH v9 1/4] i2c: tegra: Do not configure DMA if not supported

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Message-ID: <562719dc-99f1-470e-935e-a19dbfcba92f@nvidia.com>
Date: Tue, 28 Oct 2025 16:09:55 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Akhil R <akhilrajeev@...dia.com>
Cc: andi.shyti@...nel.org, conor+dt@...nel.org, devicetree@...r.kernel.org,
 digetx@...il.com, kkartik@...dia.com, krzk+dt@...nel.org,
 ldewangan@...dia.com, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org, robh@...nel.org,
 thierry.reding@...il.com
Subject: Re: [PATCH v9 1/4] i2c: tegra: Do not configure DMA if not supported


On 28/10/2025 13:08, Akhil R wrote:
> On Tue, 28 Oct 2025 10:41:54 +0000 Jon Hunter wrote:
>> On 28/10/2025 10:00, Akhil R wrote:
>>> On Fri, 24 Oct 2025 16:20:09 +0100, Jon Hunter wrote:
>>>> On 01/10/2025 07:47, Kartik Rajput wrote:
> 
> ...
> 
>>>>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>>>>> index e533460bccc3..aa7c0d8c0941 100644
>>>>> --- a/drivers/i2c/busses/i2c-tegra.c
>>>>> +++ b/drivers/i2c/busses/i2c-tegra.c
>>>>> @@ -449,6 +449,11 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
>>>>>          if (IS_VI(i2c_dev))
>>>>>                  return 0;
>>>>>   
>>>>> +     if (!of_property_present(i2c_dev->dev->of_node, "dmas")) {
>>>>> +             dev_dbg(i2c_dev->dev, "DMA not available, falling back to PIO\n");
>>>>> +             return 0;
>>>>> +     }
>>>>> +
>>>>>          if (i2c_dev->hw->has_apb_dma) {
>>>>>                  if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA)) {
>>>>>                          dev_dbg(i2c_dev->dev, "APB DMA support not enabled\n");
>>>>
>>>> What about ACPI based devices?
>>>
>>> The of_ function returns false if using ACPI. Since these DMA drivers does
>>> not support ACPI enumeration currently, we would not require to proceed
>>> further anyway. But if required we can add an additional check with
>>> acpi_dma_supported() or similar. Do you suggest adding a check for ACPI?
>>
>> I was just wondering if it is better to use fwnode_property_present()
>> instead.
> 
> I think ACPI does not use 'dmas' property to connect a DMA resource.
> It uses FixedDMA or something similar. It may not be helpful to use
> fwnode_*() or device_*() check here in that case.

OK. Then fine to leave this as-is.

Jon

-- 
nvpublic