linux-kernel - Re: [PATCH RESEND 1/2] i2c: tegra: Add GPCDMA support

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Message-ID: <ebb0764f-db92-d69d-49ac-151f4e3e0b8a@collabora.com>
Date:   Mon, 22 Aug 2022 12:45:38 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Akhil R <akhilrajeev@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        Jonathan Hunter <jonathanh@...dia.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>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "wsa@...nel.org" <wsa@...nel.org>
Subject: Re: [PATCH RESEND 1/2] i2c: tegra: Add GPCDMA support

On 8/22/22 09:56, Akhil R wrote:
>> 19.08.2022 18:15, Dmitry Osipenko пишет:
>>> 19.08.2022 15:23, Akhil R пишет:
>>>>      if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi"))
>>>>              i2c_dev->is_vi = true;
>>>> +    else
>>>> +            i2c_dev->dma_support = !!(of_find_property(np, "dmas",
>>>> + NULL));
>>>
>>> 1. You leak the np returned by of_find_property().
>>>
>>> 2. There is device_property_read_bool() for this kind of
>>> property-exists checks.
> Okay. I went by the implementation in of_dma_request_slave_channel() to
> check 'dmas'.
> 
>>>
>>> 3. If "dmas" is missing in DT, then dma_request_chan() should return
>>> NULL and everything will work fine. I suppose you haven't tried to
>>> test this code.
>>
>> Although, no. It should return ERR_PTR(-ENODEV) and then you should check
>> the return code.
> Yes. Agree that it is more agnostic to check for ERR_PTR(-ENODEV). But since I
> call tegra_init_dma() for every large transfer until DMA is initialized, wouldn't
> it be better to have a flag inside the driver so that we do not have to go through
> so many functions for every attempted DMA transaction to find out that the DT
> properties don't exist?
> 
> Shall I just put i2c_dev->dma_support = true here since DMA is supported by
> hardware? It would turn false if dma_request_chan() returns something other
> than -EPROBE_DEFER.
> 
>       if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi"))
>               i2c_dev->is_vi = true;
>  +    else
>  +            i2c_dev->dma_support = true;

The code already has dma_mode for that. I don't see why another variable
is needed.

Either add new generic dma_request_chan_optional() that will return NULL
if channel is not available and make Tegra I2C driver to use it, or
handle the error code returned by dma_request_chan().

-- 
Best regards,
Dmitry