linux-kernel - Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

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Message-ID: <55ca95a0-41d9-a071-ab9d-08d26b3f8698@nvidia.com>
Date:   Tue, 7 Apr 2020 12:05:57 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <frankc@...dia.com>, <hverkuil@...all.nl>,
        <sakari.ailus@....fi>, <helen.koike@...labora.com>
CC:     <sboyd@...nel.org>, <linux-media@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver


On 4/6/20 9:11 AM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 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.

Hans/Thierry, Can you please comment on this?