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

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Message-ID: <20251028100028.67388-1-akhilrajeev@nvidia.com>
Date: Tue, 28 Oct 2025 15:30:28 +0530
From: Akhil R <akhilrajeev@...dia.com>
To: <jonathanh@...dia.com>
CC: <akhilrajeev@...dia.com>, <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 Fri, 24 Oct 2025 16:20:09 +0100, Jon Hunter wrote:
> On 01/10/2025 07:47, Kartik Rajput wrote:
>>> On Tegra264, not all I2C controllers have the necessary interface to
>> GPC DMA, this causes failures when function tegra_i2c_init_dma()
>> is called.
>>
>> Ensure that "dmas" device-tree property is present before initializing
>> DMA in function tegra_i2c_init_dma().
>>
>> Signed-off-by: Kartik Rajput <kkartik@...dia.com>
>> ---
>> v4 -> v9: Moved the condition down to have all dma checks together.
>> v2 -> v4:
>>          * Add debug print if DMA is not supported by the I2C controller.
>> v1 -> v2:
>>          * Update commit message to clarify that some I2C controllers may
>>            not have the necessary interface to GPC DMA.
>> ---
>>   drivers/i2c/busses/i2c-tegra.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> 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?

Regards,
Akhil