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Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver
To:     Sowjanya Komatineni <skomatineni@nvidia.com>,
        thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com,
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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <6014fee9-ce97-7ced-f2ba-82176b8b36db@gmail.com>
Date:   Mon, 6 Apr 2020 19:11:30 +0300
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06.04.2020 18:41, Sowjanya Komatineni пишет:
> 
> On 4/5/20 2:11 PM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 04.04.2020 04:25, Sowjanya Komatineni пишет:
>> ...
>>> +static int tegra_vi_tpg_channels_alloc(struct tegra_vi *vi)
>>> +{
>>> +     struct tegra_vi_channel *chan, *tmp;
>>> +     unsigned int port_num;
>>> +     unsigned int nchannels = vi->soc->vi_max_channels;
>>> +     int ret = 0;
>>> +
>>> +     for (port_num = 0; port_num < nchannels; port_num++) {
>>> +             /*
>>> +              * Do not use devm_kzalloc as memory is freed immediately
>>> +              * when device instance is unbound but application
>>> might still
>>> +              * be holding the device node open. Channel memory
>>> allocated
>>> +              * with kzalloc is freed during video device release
>>> callback.
>>> +              */
>>> +             chan = kzalloc(sizeof(*chan), GFP_KERNEL);
>> Why anyone would want to unbind this driver in practice?
>>
>> I think it should make more sense to set suppress_bind_attrs=true.
> 
> From the previous feedback of patch series, we need to support
> unbind/bind and looks like this driver should also support to built as a
> module.

If module unloading is also affected, then perhaps you should use
get/put_device() to not allow freeing the resources until they're still
in-use.

I suppose that it should be up to the V4L core to keep the device alive
while needed, rather than to put the burden to the individual drivers.